phy notes manhatten
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Chapter 1Chapter 1Light and ReflectionLight and Reflection
by Mirrorsby Mirrors1.11.1 LightLight
1.21.2 Reflection of LightReflection of Light1.31.3 Curved MirrorsCurved Mirrors
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Section 1.1Section 1.1
LightLight
Properties of light Luminous and non-luminous
objects Light rays and light beams
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Why is there an image?Reason: Light travels in straight lines
When light is blocked by an objectforms an object-liked shadow
Properties of light1.1 Light (SB p.3)
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Why can light heat up an object and
power a solar calculator?
Reason:Light is a form of energy
Properties of light1.1 Light (SB p.4)
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Why can we see objects around us?
Reason: Light from these objects enters our eyes
Objectsemit light by themselves
cannot emit light
luminous
non-luminous
Luminous and non-luminous objects1.1 Light (SB p.4)
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Which of the following is/are luminous object(s)?
Luminous and non-luminous objects1.1 Light (SB p.4)
emit light by themselvesObjects
cannot emit light
luminous
non-luminous
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Which of the following is non-luminous object?Why can we see non-luminous objects?
Reason:
They reflect light fromother luminous sources
Luminous and non-luminous objects1.1 Light (SB p.5)
emit light by themselvesObjects
cannot emit light
luminous
non-luminous
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Light ray path for the propagationof light
One light ray Three light rays
Light rays and light beams1.1 Light (SB p.5)
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Light rays
divergent parallel convergent
Light rays and light beams1.1 Light (SB p.5)
divergent parallel convergent
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divergent parallel convergent
Light rays and light beams1.1 Light (SB p.5)Light rays
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Light rays
divergent parallel convergent
Light rays and light beams1.1 Light (SB p.5)
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Light beam collection of light rays
Light rays and light beams1.1 Light (SB p.6)
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Look at an object light rays from the
object enter our eyes
only draw two lightrays to the eye
Diagrammatic representation illustrate the size:
draw two light raysfrom the tip and thefoot of the object tothe eye
Light rays and light beams1.1 Light (SB p.6)
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diverging rays
parallel rays
From a near object
From a very far object
from near object
from very far object
Light rays and light beams1.1 Light (SB p.6)
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Section 1.2Section 1.2
Reflection of LightReflection of Light
Laws of reflection Formation of image by plane
mirror Applications of plane mirrors
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Reflection when a light ray strikes a surface, it is reflected from the surface
incident ray reflected ray
1.2 Reflection of light (SB p.6)
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Incident ray incoming light ray on the mirror Reflected ray light ray reflected from the
mirror
incident ray reflected ray
1.2 Reflection of light (SB p.6)
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Normal an imaginary line perpendicular to the surface at which the lightray strikes
Incidentpoint
incident ray normal reflected ray
1.2 Reflection of light (SB p.6)
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Angle of incidence (i) angle between the incident ray and the normal
Angle of reflection (r ) angle between the reflectedray and the normal
incident ray normal reflected ray
i r
1.2 Reflection of light (SB p.7)
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Laws of reflection:(i) Angle of reflection ( r ) = Angle of incidence ( i )
(ii) The incident ray , the reflected ray and thenormal all lie in the same plane
incident ray normalreflected ray
Laws of reflection1.2 Reflection of light (SB p.8)
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When parallel light rays are incident on a
smooth surface rough surface regular reflection reflected rays are parallel sharp and clear image
Laws of reflection1.2 Reflection of light (SB p.8)
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When parallel light rays are incident on a
diffuse reflection reflected rays are not parallel
blurred image
smooth surface rough surface regular reflection
Laws of reflection1.2 Reflection of light (SB p.9)
f b l
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Plane mirror plane glass, coated with a thin layer of metal regular reflection takes place
(form clear images)
glassthin layer of metalcoating
Formation of image by plane mirror 1.2 Reflection of light (SB p.10)
F i f i b l i
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Experiment 1B:Experiment 1B: Formation of image by a plane mirror
Expt. VCD
Formation of image by plane mirror 1.2 Reflection of light (SB p.10)
F i f i b l ifl f l h ( )
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When the reflected rays are extendedbackwards,
image of thelight bulb
they meet at a point (position of the image ( I ))
Formation of image by plane mirror 1.2 Reflection of light (SB p.11)
lightbulb
F i f i b l i1 2 R fl i f li h (SB 11)
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Distance between the object and the mirror = Distance between the image and the mirror
Formation of image by plane mirror 1.2 Reflection of light (SB p.11)
Object distance ( u ) = Image distance ( v )
lightbulb
F ti f i b l i1 2 R fl i f li h (SB 12)
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Construction rules for images formed byplane mirror 1. Draw an arrow
(object)2. Draw the reflected
rays from the tip of the arrow (laws of reflection)
3. Extend the reflectedrays backwards
4. Draw the reflectedrays from the foot of the arrow
5. Draw a dotted arrow(image)
object image
Formation of image by plane mirror 1.2 Reflection of light (SB p.12)
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Formation of image b plane mirror1 2 R fl ti f li ht (SB 13)
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pq
r s
object
Class Practice 1Class Practice 1 An object ( O), represented by anarrow, is placed in front of a plane mirror. Four rays, p, q, r and
s are drawn from the object to the mirror as shown in thefollowing figure. Draw the reflected rays and locate the image( I ).
Answer
image
Formation of image by plane mirror 1.2 Reflection of light (SB p.13)
Formation of image by plane mirror1 2 R fl ti f light (SB 14)
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Class Practice 2Class Practice 2 : A clock is placed in front of a planemirror. What is the time shown in the clock?
10:10
Answer
Formation of image by plane mirror 1.2 Reflection of light (SB p.14)
Applications of plane mirrors1 2 Reflection of light (SB p 15)
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Applications of plane mirrors
The wordsare laterallyinverted
1. Rear-view mirror see the traffic behind images are laterally inverted
Applications of plane mirrors1.2 Reflection of light (SB p.15)
Applications of plane mirrors1 2 Reflection of light (SB p 16)
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2. Periscope see things over an obstacle
ray fromfar object
Applications of plane mirrors1.2 Reflection of light (SB p.16)
Applications of plane mirrors1 2 Reflection of light (SB p 17)
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3. Dressing mirror
used inwashrooms andfitting rooms
4. Interior decoration
make a place lookspacious
Applications of plane mirrors1.2 Reflection of light (SB p.17)
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Section 1.3Section 1.3 Curved MirrorsCurved Mirrors
Terminology for curved mirrors Construction rules for images formed by
curved mirrors Formation of images by curved mirrors Magnification Image nature of curved mirrors
Finding the focal length of a concave mirror Applications of concave mirrors Applications of convex mirrors
1 3 Curved mirrors (SB p 19)
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Curvedmirrors
concave mirrors
convex mirrors
reflecting surfacecurves inwards
convexmirror
reflecting surfacecurves outwards
concavemirror
reflectingsurface
reflecting
surface
1.3 Curved mirrors (SB p.19)
1 3 Curved mirrors (SB p 19)
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Curved
mirrors
cylindricalmirrors
sphericalmirrors
cylindricalconcave mirror
cylindricalconvex mirror
cylindricalconcave mirror
cylindricalconvex mirror
cylindricalconcave mirror
cylindricalconvex mirror
1.3 Curved mirrors (SB p.19)inner reflectingsurface of acylinder
outer reflectingsurface of acylinder
1 3 Curved mirrors (SB p 19)
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Curved
mirrors
cylindricalmirrors
sphericalmirrors
sphericalconcave
mirror
sphericalconvexmirror
sphericalconvex mirror
sphericalconcavemirror
1.3 Curved mirrors (SB p.19)
spherical concavemirror
spherical convexmirror
inner reflecting surface
of a sphere
outer reflecting surfaceof a sphere
1 3 Curved mirrors (SB p 20)
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When parallel light rays are incident on a
concave mirror
convex mirror
reflected rays converge
reflected rays diverge
convergingmirror
divergingmirror
1.3 Curved mirrors (SB p.20)
concave mirror convex mirror
Terminology for curved mirrors1 3 Curved mirrors (SB p 20)
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1. pole ( P )
3. radius of curvature ( r )4. principal axis
2. centre of curvature ( C )
1. pole ( P )2. centre of curvature ( C )
3. radius of
curvature ( r )
Terminology for curved mirrorsconcavemirror
convexmirror
Terminology for curved mirrors1.3 Curved mirrors (SB p.20)
4. principal axis
Terminology for curved mirrors1 3 Curved mirrors (SB p 21)
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Experiment 1C:Experiment 1C: Reflection of light by
concave and convex mirrorsExpt. VCD
Terminology for curved mirrors1.3 Curved mirrors (SB p.21)
Terminology for curved mirrors1.3 Curved mirrors (SB p.22)
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focus ( F )
When parallel light rays are incident on a concave mirror convex mirror
reflected light rays converge to a point principal focus
or focus ( F )
principalaxis
Terminology for curved mirrors1.3 Curved mirrors (SB p.22)
Terminology for curved mirrors1.3 Curved mirrors (SB p.22)
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focus ( F )
When parallel light rays are incident on a concave mirror
convex mirror reflected rays converge to a point
focus ( F )
e o ogy o cu ved o s1.3 Curved mirrors (SB p.22)
reflected rays diverge , when theyextended backwards, they meet ata point
Terminology for curved mirrors1.3 Curved mirrors (SB p.22)
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Focal plane
Focal length ( f )
cuts F , perpendicular to theprincipal axis
distance between F and P = r 1
2
focalplanefocalplane
gy1.3 Curved mirrors (SB p.22)
Construction rules for images1.3 Curved mirrors (SB p.22)
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Graphical symbols
concave mirror convex mirror
formed by curved mirrors( p )
Construction rules for images formed1.3 Curved mirrors (SB p.23)
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1. Parallel to theprincipal axis
Construction rules for images formed byconcave mirrors
pass through F
by curved mirrors( p )
Construction rules for images formed1.3 Curved mirrors (SB p.23)
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2. Towards F parallel to theprincipal axis
by curved mirrors( p )
Construction rules for images formed byconcave mirrors
Construction rules for images formed1.3 Curved mirrors (SB p.23)
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3. Towards C reflected along thesame path as theincident ray
by curved mirrors( p )
Construction rules for images formed byconcave mirrors
Construction rules for images formed1.3 Curved mirrors (SB p.23)
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4. Strikes the pole atan angle
r = i
ir
by curved mirrors( p )
Construction rules for images formed byconcave mirrors
Construction rules for images formed1.3 Curved mirrors (SB p.23)
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Ray 2 is the reverse of ray 1Principal of reversibility of light
light ray will retraceits original path
Reason: Principal of reversibility of light
ray 1
ray 2
If a light ray isreversed in direction
by curved mirrors( p )
Construction rules for images formed1.3 Curved mirrors (SB p.24)
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1. Parallel to theprincipal axis
passes through F after extendedbackwards
by curved mirrors
Construction rules for images formed byconvex mirrors
Construction rules for images formed1.3 Curved mirrors (SB p.24)
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2. Towards F parallel to theprincipal axis
by curved mirrors
Construction rules for images formed byconvex mirrors
Construction rules for images formed1.3 Curved mirrors (SB p.24)
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3. Towards C reflected alongthe same path asthe incident ray
by curved mirrors
Construction rules for images formed byconvex mirrors
Construction rules for images formed1.3 Curved mirrors (SB p.24)
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4. Strikes the pole atan angle
r = i
ir
by curved mirrors
Construction rules for images formed byconvex mirrors
Formation of images by curved mirrors1.3 Curved mirrors (SB p.25)
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Experiment 1D:Experiment 1D: Formation of image by
concave and convex mirrorsExpt. VCD
Formation of images by curved mirrors1.3 Curved mirrors (SB p.26)
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Locate the images formed byconcave mirror using graphical method
1. Draw an arrow (object)2. Draw two special light
rays from the tip of theobject
3. Draw the reflectedrays to meet at apoint
4. Draw an arrow (image)
Nature of images formed by a concave mirror changes with the position of the object
Formation of images by curved mirrors1.3 Curved mirrors (SB p.26)
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1. Draw an arrow (object)2. Draw two special light
rays from the tip of theobject
3. Extend the reflectedrays backwards andintersect at a point
4. Draw a dotted line
arrow (image)Nature of images formed bya convex mirror inverted, virtual and diminished
Note: Virtual images cannot be formed on thescreen, you observe them by looking into the mirrors
directly.
Locate the images formed byconvex mirror using graphical method
Magnification1.3 Curved mirrors (SB p.27)
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Magnification ( m ) =Height of image ( h i)
Height of object ( h o)
= Image distance ( v )Object distance ( u )
u
v
similar
triangles
ho
hi
m (plane mirror) = 1
concave mirror
principalaxis
Magnification1.3 Curved mirrors (SB p.28)
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Class Practice 3Class Practice 3 (a)(a) An object ( O) is placed at 20 cm in front of a concave
mirror of focal length 40 cm as shown in the followingfigure. Draw two light rays to locate the image ( I ). Use ascale of 1 cm to represent 10 cm in the horizontal axis.
Answer
I
Magnification1.3 Curved mirrors (SB p.29)
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Class Practice 3 (Contd)Class Practice 3 ( Contd) (b)(b) Find the image distance. Hence, find the magnification.
Image distance = ______________
Magnification =
=
=
) () (
) () ( Ans
wer
4 10 = 40 cm
Image distance
Object distance40
20
2
Magnification1.3 Curved mirrors (SB p.30)
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Class Practice 4Class Practice 4
(a)(a) The positions of an object and its image formed by aconvex mirror are shown in the following figure.Locate the principal focus ( F ) of the mirror in thefigure.
Answer
Magnification1.3 Curved mirrors (SB p.30)
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Class Practice 4 (Contd)Class Practice 4 ( Contd)
(b)(b) Find the focal length and magnification of the mirror. Use a scale of 1 cmto represent 2 cm in the horizontal axis.
Focal length of the mirror =
Magnification =
=
=
) () (
) () (
Answer
4 2 = 8 cm
Image distance
Object distance
2 2
4 2
0.5
Image nature of curved mirrors1.3 Curved mirrors (SB p.31)
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1. Object is placed
between P and F Image is formed
behind the mirror Nature of image virtual erect laterally inverted
magnified(m > 1)
Nature of image formed by a concave mirror
object
image
Image nature of curved mirrors1.3 Curved mirrors (SB p.31)
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2. Object is placed at F
Image isformed at
infinity Nature of
image
cannot bedetermined
object
Nature of image formed by a concave mirror
Image nature of curved mirrors1.3 Curved mirrors (SB p.31)
f f d b
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3. Object is placedbetween F and C
Image is formedbeyond C
Nature of image real inverted magnified
(m > 1)
objectimage
Nature of image formed by a concave mirror
Image nature of curved mirrors1.3 Curved mirrors (SB p.32)
N f i f d b i
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4. Object is placed at C
Image is formedat C
Nature of image real inverted
same size asthe object(m = 1)
object image
Nature of image formed by a concave mirror
Image nature of curved mirrors1.3 Curved mirrors (SB p.32)
N f i f d b i
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5. Object is placed beyondC
Image is formedbetween C and F
Nature of image real inverted
diminished(m < 1)
object image
Nature of image formed by a concave mirror
Image nature of curved mirrors1.3 Curved mirrors (SB p.32)
N f i f d b i
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6. Object is placed at
infinity Image is formedon the focal plane
Nature of image real inverted diminished
(m < 1)
image
Nature of image formed by a concave mirror
Image nature of curved mirrors1.3 Curved mirrors (SB p.32)
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Class Practice 5Class Practice 5 : The figureshows the image formed when a toy
is placed in front of a concave mirror.
Answer
(b)(b) State the approximate position of the toy being placed.
The toy is placed .
The image is virtual, erectand magnified.
between F and the mirror
(a)(a) State the nature of the image.
Image nature of curved mirrors1.3 Curved mirrors (SB p.33)
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Note: When the object isplaced at infinity , the image isformed on the focal plane.
Image is formedbetween F and P
Nature of image
virtual erect diminished
(m < 1) laterally
inverted
object
image
Nature of image formed by a convex mirror Object is placed at any position
Image nature of curved mirrors1.3 Curved mirrors (SB p.34)
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Class Practice 6Class Practice 6 : A toy is placed in front of a convexmirror at two different object distances. The images formed
are as follows:
case 1 case 2
Image nature of curved mirrors1.3 Curved mirrors (SB p.34)
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Answer
Class Practice 6 (Contd)Class Practice 6 ( Contd) Use a ray diagram to account for the difference in image size.
The image size in case 1 is than that in case 2 because.
the toy is placed nearer to the mirror
larger
E i t 1EExperiment 1E:Finding the focal length of a concave mirror 1.3 Curved mirrors (SB p.35)
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Experiment 1E:Experiment 1E: Finding the focal length of a concave mirror
Expt. VCD
Object at infinitFinding the focal length of a concave mirror 1.3 Curved mirrors (SB p.35)
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Image distance = Focal length of the concave mirror
Object at infinityconcave mirror converges the parallel rays on
the focal plane
principalaxis
focallength ( f )focal
plane
parallellight rays
Al i h d fi d h f l l hFinding the focal length of a concave mirror 1.3 Curved mirrors (SB p.36)
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Alternative method to find the focal lengthof a concave mirror
Object at C of a concave mirror Size of image = Size of object Image distance = Object distance = r
r
2f =r
object image
Applications of concave mirrors1.3 Curved mirrors (SB p.37)
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1. Shaving and make-
up mirrorsFaces within F of themirror magnified anderect image
2. Solar furnace
Sunlight converges to thefocus high light intensity andtemperature at the focus
Applications of concave mirrors
fl
Applications of concave mirrors1.3 Curved mirrors (SB p.38)
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3. Reflector
Car headlamp
Torches Concave mirror used in surgery
D o y o u k n o w
r e f l e c t o r s
a r e n o t s p h e r
i c a l i n s h a
p e ?
Light source at the focus of the concave mirror
reflected beams are parallel
Applications of concave mirrors1.3 Curved mirrors (SB p.39)
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Not all reflected rayscan converge to thefocus
All reflected rayscan converge tothe focus
3. ReflectorsSpherical
concave mirror
Parabolic
concave mirror
Applications of concave mirrors1.3 Curved mirrors (SB p.39)
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plane mirror
eyepiece
4. Reflecting telescope
Applications of convex mirrors1.3 Curved mirrors (SB p.40)
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provides a wider field of view
image formedis diminished
plane mirror
convex mirror
Applications of convex mirrors
Applications of convex mirrors1.3 Curved mirrors (SB p.40)
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1. Rear-view mirror see the things behind
2. Security mirror prevent shoplifting
3. Road safety
mirror see round a bend
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Manhattan Press (H.K.) Ltd. 2001
Chapter 2Chapter 2Refraction2.12.1 Refraction of LightRefraction of Light2.22.2 Laws of RefractionLaws of Refraction
2.32.3 Examples of RefractionExamples of Refraction
2.42.4 Total Internal ReflectionTotal Internal Reflection
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Section 2.1Section 2.1
Refraction of LightRefraction of Light
Refraction when light ray travels from one2.1 Refraction of light (SB p.53)
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Manhattan Press (H.K.) Ltd. 200184
Refraction when light ray travels from onemedium to another medium
travelling direction of the light ray changes
incident
ray
refractedray
emerging
ray
Note:Light ray can travelin different media(e.g. air, water andglass).
air
glass
Wh d h li h f i2.1 Refraction of light (SB p.53)
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Where does the light ray refract inthe glass?
Refraction 1:from air to glass
Refraction 2from glass to air
air glass
air
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Manhattan Press (H.K.) Ltd. 2001
Section 2.2Section 2.2
Laws of RefractionLaws of Refraction
Refractive index
Wh li ht t l f i t l2.2 Laws of refraction (SB p.54)
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When a light ray travels from air to glass ,
light rayrefracted ray (strong)
reflected ray (weak)
incident ray reflected ray
air
glass
interface
refractedray
N l h h i id i2.2 Laws of refraction (SB p.54)
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Normal pass through incident point,perpendicular to the air-glass interface
normal
Incidentpoint
incident ray reflected ray
air
glass
interface
refractedray
A l f i id ( i)angle between the incident
2.2 Laws of refraction (SB p.54)
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Angle of incidence ( i ) ray and the normal
Angle of refraction ( r ) angle between the refracted ray and the normal
i
r
incident ray reflected ray
air
glass
interface
refractedray
normal
E i t 2AExperiment 2A:2.2 Laws of refraction (SB p.54)
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Experiment 2A:Experiment 2A: Refractive index of glass
Intro. VCD
Expt. VCD
A li h l f i l bli l
2.2 Laws of refraction (SB p.55)
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normal
A light ray travels from air to glass obliquelyIt bends towards the normal
original path of the light ray
G raph of sin i2.2 Laws of refraction (SB p.55)
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G raph of sin i against sin r
1. pass through theorigin
sin i sin r = constant2.
2.2 Laws of refraction (SB p.56)
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94
Laws of refraction
1. The incident ray, therefracted ray and thenormal all lie in thesame plane
sin i sin r
= constant2.
Note: It is also calledSnells law.
normal
air
glass
Interface
strongrefracted ray
incidentray
weakreflected ray
When a light ray travels fromRefractive index2.2 Laws of refraction (SB p.56)
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95
When a light ray travels from1. air to glass
2. glass to air
refracted ray bends towards
the normalrefracted ray bends away fromthe normal(principle of reversibility of light)
air
glass
normal
air
glass
normal
Refractive index2.2 Laws of refraction (SB p.56)
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Refractive index
of glass (n
g)
When a light ray travels from air to glass
sin i sin r
Refractive index
sin
a
sin gn g =
air
glass
normal
i
r =
What is theRefractive index2.2 Laws of refraction (SB p.57)
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97
Method 1 n g = Slope of the graph
= 1.5
What is therefractive index of glass ( n g)?
Method 2
Apply the equation:n
g sin asin g
=
Refractive index2.2 Laws of refraction (SB p.57)
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98
Refractive indices of some materials
(n )1.00
1.0003 1.00
1.33
1.36
1.50
1.50 1.70
2.42
Material Refractive index ( n )
VacuumAir
Water AlcoholPerspex
Glass
Diamond
Different materials haveRefractive index2.2 Laws of refraction (SB p.57)
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Different materials havedifferent refractive indices
different angle of refraction ( r 1
r 2)
nw = 1.33 ng = 1.5
r 1
r 2
air
water
normal
glass
air
normal
n (1 33) < n (1 5)Refractive index2.2 Laws of refraction (SB p.58)
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nw (1.33) < n g (1.5)
refracted ray in glass bendstowards the normal more (r 1 > r 2)
nw = 1.33 ng = 1.5
r 1
r 2
air
water
normal
glass
air
normal
Optically denser medium a medium with greater n
Refractive index2.2 Laws of refraction (SB p.58)
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Optically denser medium
Optically less dense medium
a medium with greater n
a medium with
smaller nglass ( n g = 1.5)
water ( n w = 1.33)
optically denser mediumoptically less dense medium
nw = 1.33 ng = 1.5 air
water
normal
glass
air
normal
A light ray travels from anRefractive index2.2 Laws of refraction (SB p.58)
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optically denser medium
optically lessdense medium
normal
optically less dense medium
optically denser mediumrefracted raybends towards the normal
A light ray travels from an
Refractive index2.2 Laws of refraction (SB p.58)
A light ray travels from an
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optically lessdense medium
optically denser medium
normal
refracted ray
bends away fromthe normal
A light ray travels from anoptically denser medium
optically less dense medium
Class Practice 1Class Practice 1 : A light ray travels from air to water as
Refractive index2.2 Laws of refraction (SB p.59)
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AnswerClick for answer now!!
Class Practice 1Class Practice 1 : A light ray travels from air to water asshown in the following figure.
(a)(a) Find the angle of reflection and theangle of refraction. The refractiveindex of water ( nw) is 1.33.
Angle of reflection =_______
75o
air
water
=
=
=
6.46
sin75sin33.1
sinsin
w
w
w
aw
By Snells Law,
Class Practice 1 (Contd)Class Practice 1 (
Contd)
Refractive index2.2 Laws of refraction (SB p.60)
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air
water
(b)(b) Sketch the reflected and refracted rays in the
figure.
Class Practice 1 (Cont d)Class Practice 1 ( Cont d)
AnswerClick for answer now!!
reflectedray
air
water
refractedray
Class Practice 2Class Practice 2 : A light ray travels through a glass
Refractive index2.2 Laws of refraction (SB p.60)
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Class Practice 2Class Practice 2 : A light ray travels through a glass prism as shown in the following figure. The refractive indexof the prism is 1.5. Find the angles i, a , b, c and d . Hence,find angle r .
=
=
==
==
==
=
=
==
4.52
5.1sinsin
9.311.5890
1.589.6160180
9.611.2890
1.28
5.1sin
sin
454590
r
d
r
d
c
b
aa
i
i
AnswerClick for answer now!!
normal
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Section 2.3Section 2.3
Examples of RefractionExamples of Refraction
Real depth and apparent depth Refraction by prism
2.3 Examples of refraction (SB p.61)
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Experiment 2B:Experiment 2B: Refraction of light
Expt. VCD
Light rays are refracted at the
Real depth and apparent depth2.3 Examples of refraction (SB p.62)
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in the absenceof water
Light rays cannot reach the eye
g ywater-air interface
light rays can reach the eye
Note: The objectappears raised.
Refracted rays extendbackwards (dotted lines)
and meet at a point(position of image)
air water
distance between the water
Real depth and apparent depth2.3 Examples of refraction (SB p.62)
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Real depth ( D )
Apparent depth ( D)
surface and the object
real depth
distance between the water surface and the image
apparentdepth
Prism triangular glass prism
Refraction by prism2.3 Examples of refraction (SB p.63)
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Prism triangular glass prism when a white light passes through it,
a spectrum of different colours isformed
spectrum
whitelight
prism
redorangeyellowgreenblue
indigo
violet
Wh i f d?
Refraction by prism2.3 Examples of refraction (SB p.63)
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Why is a spectrum formed?
Reason: White light consists of different coloursdifferent colours have
different refractive indices
refract at differentangles of refraction
dispersion of white light
whitelight
prism
redorangeyellowgreenblue
indigoviolet
Class Practice 3Class Practice 3 : A huntsman sees a shark in the water
Refraction by prism2.3 Examples of refraction (SB p.64)
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Class Practice 3Class Practice 3 : A huntsman sees a shark in the water as shown in the figure below.
Answer!Click for answer now!!
(a)(a) Locate the apparent position of the shark in the figure.
shark
apparent position of the shark
Cl P i 3 (C d)Cl P ti 3 (
C td)
Refraction by prism2.3 Examples of refraction (SB p.64)
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(b)(b) The shark appears to be (smaller/larger) in size, because the shark appears to be at a position
(farther away from/nearer to ) thewater surface.
Class Practice 3 (Contd)Class Practice 3 ( Contd)
larger
Answer!Click for answer now!!
nearer to
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Section 2.4Section 2.4Total Internal ReflectionTotal Internal Reflection
Critical angle Examples of total internal reflection
Applications of total internalreflection
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At a small angle refracted ray (strong)2.4 Total internal reflection (SB p.65)
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gof incidence ( i )
y ( g) reflected ray (weak)
partialreflected rayincident ray
air water
normal partialrefracted
ray
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Angle of refraction r refracted ray (weak)2.4 Total internal reflection (SB p.65)
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g= 90
angle of incidence ( i ) = critical angle ( c )
y ( )
reflected ray (strong)
critical angle ( c )
i
incidentray
partialreflected ray
air
water
normal
partialrefracted ray
Angle of incidence ( i )C i i l l
no refracted ray2.4 Total internal reflection (SB p.65)
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> Critical angle reflected ray only
This phenomenon is calledtotal internal reflection
i i
incidentray
totalreflected
ray
air
water
normal
Two conditions for the occurrence of
2.4 Total internal reflection (SB p.66)
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Two conditions for the occurrence of total internal reflection
1. Light ray travels froman optically denser medium (water) to anoptically less dense medium (air)
2. Angle of incidence (i ) > Critical angle (
c ) of the optically denser
medium (water)
incidentray
totalreflected ray
air
water
normal
Experiment 2C:Experiment 2C: 2.4 Total internal reflection (SB p.66)
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Critical angle and total internal reflection
Expt. VCD
Calculate the critical angle ( c ) of glassCritical angle2.4 Total internal reflection (SB p.68)
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g ( ) g
ng
sin asin g
=
sin 90 o
sin c =
ng = 1.5 c = 42 o
By Snells Law,
air
glass
c = sin 1 ( )1n
g
Critical angles of some materialsCritical angle2.4 Total internal reflection (SB p.68)
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Critical angles of some materials
( n ) ( c )1.33 = 8.48)33.1
1(sin 1
1.50 = 8.41)
5.11(sin 1
2.42 = 4.24)42.21
(sin 1
c = sin 1 ( )1n
Material
Water
GlassDiamond
Refractive index ( n ) Critical angle ( c )
Class Practice 4Class Practice 4 : A light ray travels from water to air.
Critical angle2.4 Total internal reflection (SB p.69)
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Describe the changes in the brightness of the refracted rayand the reflected ray when the angle of incidence ( i) increasesfrom 0 to 60. The critical angle of water is 48.8.
When 0 < i < 48.8 , _____________________________.
When i = 48.8 , __________________________________.
When i > 48.8 , __________________________________.
a weak reflected ray and astrong refracted ray are
observed.
a strong reflected ray appears and aweak refracted ray emerges along
the water-air boundary.
the ligh t ray is totally reflected at thewater-air boundary and the reflectedray becomes as bright as the incident
ray. No refracted ray is observed.
AnswerClick for answer now!!
Class Practice 5Class Practice 5 : Referring to the following figure,t th f ll i g t t tT l i l fl i d
Critical angle2.4 Total internal reflection (SB p.69)
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comment on the following statement:Since the angle of incidence (60) is greater than the critical
angle of glass (41.8), total internal reflection will occur.
air
glass
Is this statement correct? Explain briefly.
Answer!Click for answer now!!
Total internal reflection does not occur because air is optically less dense than glass.
Total internal reflection only occurs when lighttravels from an optically denser medium to an
optically less dense one.
Examples of total internal reflection
Examples of total internal reflection2.4 Total internal reflection (SB p.70)
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1. Sparkle of diamond
Why is diamond more brilliant than glass?Light rays enter the diamond fromabove undergo total internal reflection
at the bottom emerge from the top surface
give brilliant colour
Reason: Critical angle of diamond (24 o )
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Why is there a mirage?2. Mirage
Reason: Light rays enter from cold air toExamples of total internal reflection2.4 Total internal reflection (SB p.71)
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total internalreflection
hot air (different media), then refraction
and total internal reflection (at A
) occur.eye of the observer
hot air
cold air
3. Scene under water Examples of total internal reflection2.4 Total internal reflection (SB p.72)
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Can the diver see the object behind the barrier?
Yes, because light rays undergo totalinternal reflection on the water surface
Experiment 2D:Experiment 2D: Applications of total internal reflection2.4 Total internal reflection (SB p.72)
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Construction of a prismatic periscope
Expt. VCD
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Class Practice 6Class Practice 6 : Is the image formed by a periscope
Applications of total internal reflection2.4 Total internal reflection (SB p.74)
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real or virtual? Complete the following ray diagram andanswer the question.
The image formed by a periscope is .virtual
object
Answer!Click for answer now!!
image
object
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3. Optical fibres for telecommunicationApplications of total internal reflection2.4 Total internal reflection (SB p.76)
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total internalreflection
p light ray undergoes total internal reflection
at the core-cladding interface
light ray a light ray emerges at theopposite end of the optical fibre
core
cladding
Reasons for using optical fibres instead of bl
Applications of total internal reflection2.4 Total internal reflection (SB p.76)
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copper cables
thinner, lighter and cheaper provide a higher bandwidth
and carry more telephonecalls at a time
avoid electrical interferenceand more secured
loss of signals is minimized
4. Optical fibres for endoscoped i i h i l
Applications of total internal reflection2.4 Total internal reflection (SB p.77)
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doctors use it to examine the internal
organs of patients
endoscope
light illuminatesthe internal organs
of the body
light is reflected back tothe detector and is
analysed by doctors
5. Fish-eye viewli h f h f b l d
Applications of total internal reflection2.4 Total internal reflection (SB p.78)
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48.8 48.8
light rays from the water surface below undergototal internal reflection on the water surface
View of fish-eye is restrictedwithin an angle of 97.6
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Chapter 3Chapter 3Lenses
3.13.1 Cylindrical and Spherical LensesCylindrical and Spherical Lenses
3.23.2 Construction Rules for ImagesConstruction Rules for ImagesFormed by LensesFormed by Lenses
3.33.3 Formation of Images by LensesFormation of Images by Lenses
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Section 3.1Section 3.1Cylindrical andCylindrical and
Spherical LensesSpherical Lenses Terminology for lenses
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Lconvex lenses the thickest at centre
3.1 Cylindrical and spherical lenses (SB p.89)
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Lensesconcave lenses the thinnest at centre
the thickest at centres of convex lenses
the thinnest at centres of concave lenses
3.1 Cylindrical and spherical lenses (SB p.89)
Lensesconvex lenses the thickest at centre
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cylindricalconvex lens
cylindricalconcave lens
sphericalconvex
lens
sphericalconcave lens
Lensesconcave lenses the thinnest at centre
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When parallel light rays pass through a3.1 Cylindrical and spherical lenses (SB p.89)
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convex lens
concave lens emerging rays diverge diverging lens
converging lens
Terminology for lenses
3.1 Cylindrical and spherical lenses (SB p.89) Terminology for lenses
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convex lens concave lens
gy
opticalcentre
principalaxis
1. Principal axis2. Optical centre ( C )
Experiment 3A:Experiment 3A: Refraction of light by convex and concave lenses
3.1 Cylindrical and spherical lenses (SB p.90) Terminology for lenses
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Refraction of light by convex and concave lenses
Expt. VCD
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convex lensWhen parallel light rays pass through a
emerging rays converge to a point
3.1 Cylindrical and spherical lenses (SB p.91) Terminology for lenses
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convex lens
concave lens
focus (F )
emerging rays converge to a point
Note: Light rays can be directed towards alens from either side, so a lens has two foci.
focus
concave lens
emerging rays diverge,extended backwards tomeet a point :
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Greater curvature of lens
3.1 Cylindrical and spherical lenses (SB p.91) Terminology for lenses
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2
1
(shorter focal length)Light rays converges
more ( 2 > 1)smaller curvature
greater curvature
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Graphical symbols
3.2 Construction rules for images formed by lenses (SB p.92)
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p y
convex lens concave lens
Construction rules for imagesf d b l
3.2 Construction rules for images formed by lenses (SB p.92)Construction rules for images
formed by convex lens
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formed by convex lens
F
1. Parallel to theprincipal axis
passes through F onthe opposite side of the incident ray
3.2 Construction rules for images formed by lenses (SB p.93)Construction rules for images
formed by convex lensConstruction rules for images formed
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F
2. Towards F parallel to theprincipal axis
F
by convex lens
3.2 Construction rules for images formed by lenses (SB p.93)Construction rules for images
formed by convex lensConstruction rules for images formed
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3. Towards C passes throughC
without deviation
by convex lens
Principle of reversibilityf li h
3.2 Construction rules for images formed by lenses (SB p.93)Construction rules for images
formed by convex lens
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The refraction of ray 2 is the reverse of ray 1
of light
Reason: The principle of reversibility of light
ray 1 ray 2
Class Practice 1 :Class Practice 1 : Referring to the figure below, an image
3.2 Construction rules for images formed by lenses (SB p.94)Construction rules for images
formed by convex lens
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Class Practice 1 :C ass act ce : g g , g I is formed when an object is placed on the left hand side of aconvex lens. Draw two light rays to locate the position of theobject as O.
Answer
3.2 Construction rules for images formed by lenses (SB p.95)Construction rules for images
formed by concave lensConstruction rules for imagesf d b l
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F
1. Parallel to theprincipal axis
appears to come from F on the same side of theincident ray
formed by concave lens
3.2 Construction rules for images formed by lenses (SB p.94)Construction rules for images
formed by concave lensConstruction rules for imagesf d b l
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F
2. Towards F parallel to theprincipal axis
formed by concave lens
3.2 Construction rules for images formed by lenses (SB p.95)Construction rules for images
formed by concave lensConstruction rules for imagesf d b l
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3. Towards C passes through C without deviation
|c
formed by concave lens
Class Practice 2Class Practice 2Draw the refracted ray in each of the following figures
3.2 Construction rules for images formed by lenses (SB p.97)Construction rules for images
formed by concave lens
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Draw the refracted ray in each of the following figures.
Answer
(a)(a)
(b)(b)
Section 3 3Section 3 3
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Section 3.3Section 3.3
Formation of ImagesFormation of Imagesby Lensesby Lenses
Locate the images by graphicalmethod
Image nature of lenses Finding the focal length of a convexlens
Experiment 3B:Experiment 3B: Formation of image by
3.3 Formation of images by lenses (SB p.97)
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convex and concave lensesExpt. VCD
Locate the images formed by convexlens by graphical method
3.3 Formation of images by lenses (SB p.98) Locate the images bygraphical method
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lens by graphical method1. Draw an arrow
(object)
2. Draw two speciallight rays from the tip
of the object3. Draw the refractedrays to meet at apoint
4. Draw an arrow(image) to theprincipal axis
Note: Image nature of convex lens changes with object distance
principalaxis
convexlens
I
O
1. Draw an arrow (object)
3.3 Formation of images by lenses (SB p.98) Locate the images bygraphical methodLocate the images formed by concavelens by graphical method
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1. Draw an arrow (object)
2. Draw two special lightrays from the tip of theobject
3. Extend the refractedray backwards to meetat a point
4. Draw an arrow (image)to the principal axis
Note: nature of imagesformed by a concave lens erect, virtual anddiminished
concave lens
I
O
e s by g ap ca et od
Note: Virtual images cannot beformed on the screen, youobserve them by looking intothe mirrors directly.
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1 Object is placed between C and FImage nature of convex lens
3.3 Formation of images by lenses (SB p.99) Image nature of lenses
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o
I
1. Object is placed between C and F
Image is formedon the same sideas the object
Nature of image virtual erect
magnified(m > 1)
image
2 Object is placed at F
3.3 Formation of images by lenses (SB p.99) Image nature of lenses
Image nature of convex lens
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o
2. Object is placed at F
Image isformed atinfinity
Nature of image
cannot bedetermined
3. Object is placed between F and 2 F
3.3 Formation of images by lenses (SB p.99) Image nature of lensesImage nature of convex lens
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o
I
j p
Image is formedbeyond 2 F on theopposite side of the lens
Nature of image real inverted
magnified(m > 1)
object
image
4. Object is placed at 2 F
3.3 Formation of images by lenses (SB p.99) Image nature of lensesImage nature of convex lens
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o
I
j p
Image is formed at2F on the oppositeside of the lens
Nature of image
real inverted same size as
object ( m = 1)
object
image
5. Object is placed beyond 2 F
3.3 Formation of images by lenses (SB p.100) Image nature of lensesImage nature of convex lens
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o Image is formedbetween F and 2 F onthe opposite side of the lens
Nature of image real inverted diminished ( m < 1)
object
image
6 Object is placed at infinity
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6. Object is placed at infinity
Image is formed onthe focal plane
Nature of image
real inverted diminished ( m < 1)
image
Class Practice 3Class Practice 3 In the following figure, sketch therefracted rays and locate the image ( I)
3.3 Formation of images by lenses (SB p.101) Image nature of lenses
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refracted rays and locate the image ( I ).
Answer
I
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(b)(b) When a boy is at position (i)(i) X and then (ii)(ii) Y, what will he
Class Practice 4 (Contd):Class Practice 4 (
Contd):
3.3 Formation of images by lenses (SB p.102) Image nature of lenses
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(b)(b) When a boy is at position (i)(i) X and then (ii)(ii) Y , what will he
see?
(i)(i) If the boy is at position X , he will see a letter _______.
(ii)(ii) If the boy is at position Y , he will see a
letter _______.
Answer
b
d
convexlens
translucentscreen
(c)(c) Draw a ray diagram to determine the image distanceClass Practice 4 (Contd)Class Practice 4 (
Contd)
3.3 Formation of images by lenses (SB p.102) Image nature of lenses
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Ans
wer
( )( ) y g g
and magnification. Use the scale shown in the figure.
Image distance = __________ = __________.
Magnification _______.
6 x10
60cm
Height of object
Height of image
105
2
Object is placed at any
3.3 Formation of images by lenses (SB p.103) Image nature of lensesImage nature of concave lens
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o I
Image is formedbetween F and C ,andon the same side asthe object
Nature of image virtual erect
diminished ( m < 1)
position
object
image
Note: When the object is placed atinfinity, the image is formed on the
f l l
larger imageFocal length of concave lens is fixed,
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Shorter objectdistance
larger image,
but must be smaller thanthe object ( m < 1)
longer objectdistance shorter objectdistance
Class Practice 5Class Practice 5 An object O is placed in front of aconcave lens. Three light rays, p, q and r are directed towardsth l h i th f ll i g fig
3.3 Formation of images by lenses (SB p.104) Image nature of lenses
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(a)(a) Sketch the refracted rays of p, q and r .(b)(b) Locate the image I .
the concave lens as shown in the following figure.
Answer
Class Practice 6Class Practice 6 The following figures show theimages formed by two lenses, L1 and L2. Name the lenses.
3.3 Formation of images by lenses (SB p.104) Image nature of lenses
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L1 is a __________ lens, and L2 is a __________ lens.
convex
Answer conc
ave
lens L1 lens L2
Class Practice 7Class Practice 7 An object O, which is 15 cm inheight, is placed at 30 cm in front of a concave lens. Thefocal length of the lens is 15 cm
3.3 Formation of images by lenses (SB p.105) Image nature of lenses
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Answer
(a)(a) Draw a ray diagram to locate the image I . Use thescale shown in the figure.
focal length of the lens is 15 cm.
(b)(b) State the nature of the image.
Class Practice 7(Contd):Class Practice 7(
Contd):3.3 Formation of images by lenses (SB p.105) Image nature of lenses
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The image is virtual, erect
and diminished.
Answer
Experiment 3CExperiment 3C Finding the focal length of a convex lens
3.3 Formation of images by lenses (SB p.105) Finding the focal length of a convex lens
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Expt. VCD
Convex lenses converge parallel light rays on
Finding the focal length of a convex lens3.3 Formation of images by lenses (SB p.106) Finding the focal length of a convex lens
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the focal planeImage distance = Focal length of convex lensparallel light
rays focal plane
principal axis
focallength ( f )
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Chapter 4Chapter 4
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Chapter 4Chapter 4Optical Instruments
4.14.1 Magnifying GlassMagnifying Glass4.24.2 Human EyeHuman Eye
4.34.3 CameraCamera
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Section 4.1Section 4.1
Magnifying GlassMagnifying Glass
What is a magnifying glass?
4.1 Magnifying glass (SB p.114)
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It is a convex lens with a short focal length
Properties of a magnifying glass (convexlens)
4.1 Magnifying glass (SB p.115)
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Object is placed within the focallength
Nature of image virtual, erect and
magnified
I
longer object distance
When focal length of a magnifying glass is fixed,4.1 Magnifying glass (SB p.115)
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longer object distance
larger magnification
shorter objectdistance
longer objectdistance
I
I
l
When object distance is fixed,4.1 Magnifying glass (SB p.116)
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thicker convex lens(shorter focal length)
larger magnification
shorter
focallength
longer
focallength I
I
Class Practice 1Class Practice 1 An object is placed in front of amagnifying glass at different positions as shown in the figurebelow Locate the images for the object at u u and u
4.1 Magnifying glass (SB p.117)
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below. Locate the images for the object at u1, u2 and u3.
Answer
I 2
I 1
I 3
Class Practice 1 (Contd)Class Practice 1 (
Contd)
I 2I1
4.1 Magnifying glass (SB p.118)
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When the object is moved from u1 to u2, the image
becomes ______________ in size, but it is still _______________ and virtual. If the object is moved
to u3, the image will become ____________,
____________ and ____________.
Answer
I 1
I 3
larger erect
magnifiedinvertedreal
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Human eye Optical instrument inside our bodies
Structure of human eye4.2 Human eye (SB p.118)
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Focus objects, perceive depths, distinguishcolours
Structure of human eye(1) cornea image
control size
Structure of human eye4.2 Human eye (SB p.118)
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(2) pupil(3) iris(4) lens(5) ciliary muscles(6) retina(7) optic nerve
cornea
lens
ciliary muscles
pupil
iris retina
Note: Images formedon the retina are realand inverted.
opticnerve
formed on it
transmitsignalsto brain
control size
of pupil
controlthickness of lens
lightrays
Control of brightness depends on thesize of pupilIn bright environment,
i i d h i f il
Control of brightness4.2 Human eye (SB p.119)
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size of pupilreduces
iris reduces the size of pupil limit the amount of light entering the eye
In dim environment, size of pupil widens
Control of brightness4.2 Human eye (SB p.119)
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increase the amount of light entering the eye
size of pupilwidens
Colour of the eye colour of the iris
Control of brightness4.2 Human eye (SB p.119)
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Looking at a distant object
Accommodation depends on thicknessof lens
Accommodation4.2 Human eye (SB p.120)
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Looking at a distant object Ciliary muscles relax Lens becomes thinner
(longer focal length)
Note:Distance between lens and retina= Focal length of lens
Looking at a near object Ciliary muscles contract
Accommodation4.2 Human eye (SB p.120)
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y
Lens becomes thicker (shorter focal length)
Accommodation See objects at different distances
Accommodation4.2 Human eye (SB p.120)
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Ciliary muscles change the lens shape Focus images on the retina
light from
distant object
light from
near object
Range of visionFar point the farthest point that an eye can
see clearly (infinity)
Defects of vision4.2 Human eye (SB p.120)
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near pointfar point
Near point see clearly (infinity)the nearest point that an eye cansee clearly (25 cm)
Note: The range of visionfor a normal eye is fromabout 25 cm to infinity.
25 cminfinity
Experiment 4A:Experiment 4A: Model eye kit experiment
Defects of vision4.2 Human eye (SB p.121)
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Expt. VCD
Short-sightedness Cannot see distant objects clearly
Defects of vision4.2 Human eye (SB p.122)
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image formedin front of the
retina
light rays fromdistant object
Cause the eyeball is too long or the lens is too thick Effect image is formed in front of the retina
Note:Near point < 25 cm(short-sighted eye)
Correction of a short-sighted eye Wear spectacles with concave lenses
Defects of vision4.2 Human eye (SB p.122)
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Wear spectacles with concave lenses
light rays fromdistant object
concave lens
light rays appear to comefrom a nearer point
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Correction of a long-sighted eyeWear spectacles with convex lenses
Defects of vision4.2 Human eye (SB p.123)
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Wear spectacles with convex lenses
convex lens
light rays fromnear object
light rays appear to
come from afarther point
Class Practice 3:Class Practice 3: Chris is suffering from short-sightedness. What kind of spectacles should he wear?
He should wear a pair of spectacles with concave lenses.
Defects of vision4.2 Human eye (SB p.123)
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Chris is now looking at a distant object. Draw on thefollowing figure to show
(i)(i) how the light rays from the distant object travelinside the eyeball without spectacles, and
(ii)(ii) how the eye defect can be corrected with thespectacles.
Answer concave lens
Class Practice 4:Class Practice 4: A short-sighted person is looking at anear object in front of him. Draw in the following figure toshow the refraction of the two light rays by his eye lens.
Defects of vision4.2 Human eye (SB p.124)
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The image is formed _________________.Answer
on the retina
light rays fromnear object
Astigmatism Form distorted images
Defects of vision4.2 Human eye (SB p.124)
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Cause asymmetry of cornea shape Correction wear a non-spherical lens
Look at this set of lines to checkwhether you are suffering from
astigmatism
Section 4.3Section 4.3
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CameraCamera
Structure of camera Factors affecting theamount of light entering a
camera Focusing
Camera functions like a human eye(1) lens(2) aperture
controls theexposure time of
Structure of camera4.3 Camera (SB p.125)
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(2) aperture(3) film(4) focusing
ring
(5) shutter
shutter
film
lens
focusing ring
aperture
image formedon the film
Note: The image formed onthe film is inverted and real.
focuses incominglight onto the film
adjusts the amountof light entering
the camera
plastic coveredwith light sensitive
chemical
adjusts the distancebetween lens and film
exposure time of the film to light
Control the amount of light entering a camera
(1) Size of aperture(2) Shutter speed
Factors affecting the amount of lightentering a camera
4.3 Camera (SB p.126)
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(1) Size of aperture
aperture
Controlled by a diaphragm (metal sheets) Control the intensity of light onto the film
diaphragm
Factors affecting the amount of lightentering a camera
4.3 Camera (SB p.127)
Control the amount of light entering a camera(2) Shutter speed
(1) Size of aperture(2) Shutter speed
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Open and closure of shutter depend on thechosen speed
Control the exposure time of the film to light
(2) Shutter speed
Focusing Properties
focusing ringfilm
Focusing4.3 Camera (SB p.127)
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p lens is mounted
on the focusing ring
Different object distance adjust the lens-to-film distance
(image distance) focus images on the film
Note: The process of adjusting
the lens-to-film distance is calledfocusing.
lens
g g
object
image
Focusing a far object Move lens close to the film
Focusing4.3 Camera (SB p.127)
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(reduce image distance)
lens
object
image
Focusing4.3 Camera (SB p.128)
Focusing a near object Moved lens away from the film
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object
image
(increase image distance)
Chapter 5Chapter 5
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Temperature, Heat andTemperature, Heat andInternal EnergyInternal Energy5.15.1 TemperatureTemperature
5.25.2 ThermometersThermometers
5.35.3 Heat and Internal EnergyHeat and Internal Energy
5.45.4 Specific Heat Capacity and EnergySpecific Heat Capacity and EnergyTransfer in Mixing ProcessTransfer in Mixing Process
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5.1 Temperature (SB p.140)
What is temperature?
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It tells how hot or cold an object is A hot body has a higher temperaturethan a cold one
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Celsius scale
5.1 Temperature (SB p.141)empera ure
scale
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In Hong Kong, the mostcommon temperature scale isCelsius scale
It was introduced by a Swedishastronomer, called AndersCelsius, in 1742
Celsiusscale
upper
Lower fixed point (or ice
empera ure
scale5.1 Temperature (SB p.142)
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upper fixed point
boilingwater
lower fixed point
melting ice
Upper fixed point (or steam
point) 100 C, temperatureof the steam over pure boilingwater at normal atmosphericpressure
point) 0 C, temperature for pure ice to melt at normalatmospheric pressure
Calibration divide theincluded region equally into 100divisions
Fahrenheit scale
5.1 Temperature (SB p.141)empera ure
scale
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1. Often used in hospitals and clinics to indicate thebody temperature
2. The melting point of ice is 32F
3. The steam point of boiling water is 212F
4. The normal body temperature is 98.6F
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Section 5.2Section 5.2ThermometersThermometers
Liquid-in glass
thermometers Other thermometers
How do you knowabout thermometers?
5.2 Thermometers (SB p.142)
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measure temperature
substance that hasthe property varieslinearly with the
temperature
Uses
Materials
Thermometer is a tool for measuringtemperature
5.2 Thermometers (SB p.142)
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Sensing propertySensing propertyProperty that varies linearlywith temperature: Length Colour
Electrical conductivity
Types of thermometers
5.2 Thermometers (SB p.146) Other thermometers
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Liquid-in-glass thermometer
Platinum resistance thermometer
Rotary thermometer Thermochromic thermometer
Liquid-in-glass thermometers
5.2 Thermometers (SB p.142) Liquid-in-glass thermometers
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Liquids in thecapillary glasstube expands or contracts linearlywith temperature
changes
Comparison of two liquid-in-glassthermometers
Mercury-in-glassthermometer
Alcohol-in-glassthermometer
5.2 Thermometers (SB p.143) Liquid-in-glass thermometers
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quick response to the changein temperature
slow response
can measure hightemperature (up to 357 C)
can measure lowtemperature (down to
110
C)mercury is poisonous, avoidinhaling its vapour once thethermometer is broken
alcohol is non-poisonous, butflammable, widely used inschool laboratories
no need to dye the liquid alcohol is colourless, it isdyed red for easier observation
more expensive cheaper
Clinical thermometers
Liquid-in-glass thermometers5.2 Thermometers (SB p.143)
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Constriction prevents the mercuryfrom falling back to thebulb, so as to maintainthe highesttemperature reading
Class Practice 1:Class Practice 1: A liquid-in-glass thermometer has column heights of 2.5 cm and 14 cm at ice point andsteam point respectively. After immersing thethermometer into an unknown liquid, the liquid column
Liquid-in-glass thermometers5.2 Thermometers (SB p.146)
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height becomes 9 cm. Find the temperature of the liquidand state the assumption you have made.Let the unknown temperature be T .
The equation is based on the assumption that the liquid expandswith the temperature increase.
Answer
=
=
T
T
)()(
)(
9 2.5
100 14 2.5
56.5C
linearly
Platinum resistance thermometer
5.2 Thermometers (SB p.146) Other thermometers
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Property resistance increases when thetemperature rises
Method measure the resistance of a platinumwire that is in contact with the object
Temperature range 200C to 1 000C
Rotary thermometer Bimetallic strip
Other thermometers5.2 Thermometers (SB p.146)
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made up of twodifferent metal strips
when temperaturerises, one of the metalstrips expands more
metal strips bends
copper iron
copper
iron
rivet
At higher temperature:
Rotary thermometer Property
5.2 Thermometers (SB p.147) Other thermometers
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consists of a coiled bimetallicstrip which bends whentemperature rises
Method
the strip coils up and movesthe pointer to indicate thetemperature
Application
measure the temperatures inovens and refrigerators
Thermochromic thermometer Property
Other thermometers5.2 Thermometers (SB p.147)
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colour changes withtemperature
Method
make use of colour to
indicate the temperatureTemperature range
20C to 40C
Application
measure the temperaturesof body and water inside afish tank
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Thermal equilibriumIf T A > T B
If T A = T Bno energy transfers and
5.3 Heat and internal energy (SB p.148) Heat
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energy transfers from A to B thermal equilibriumattains
After certaintime
energy transfers from A toB
no energy transfers
Law of conservation of energy
Heat5.3 Heat and internal energy (SB p.148)
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It states that in all energytransformation processes, energy cannotbe created or destroyed.
But energy can transfer from one body to another
change from one form to another
Heat
5.3 Heat and internal energy (SB p.149) Heat
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Heat is defined as theenergy transferred
between two bodies of different temperatures
Internal energy
5.3 Heat and internal energy (SB p.149) Internal energy
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Internal energy = Kinetic energy + Potential energy
originated frommotion of the
molecules
originated frombonding between
molecules
Intermolecular bonding
Internal energy5.3 Heat and internal energy (SB p.150)
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sphere
springpotential energy
kinetic energy
The bond between two
molecules is regardedas the spring linking twometal spheres
Temperature rises, kinetic energyincreases
5.3 Heat and internal energy (SB p.150) Internal energy
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When temperature rises molecules vibrate more
vigorously kinetic energy increases
State changes, potential energychanges
Internal energy5.3 Heat and internal energy (SB p.150)
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Weak bonds
are formed from theintermolecular attractions
between molecules are independent of indep endent of
temperaturetemp erature
Power 5.3 Heat and internal energy (SB p.151) Power
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Power =
P =
1 W = 1 J s 1
EnergyTime
E
t
e.g. A heater rated 50 W means 50 J of energy is transferred in 1 second
Section 5.4Section 5.4
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Specific Heat Capacity andSpecific Heat Capacity andEnergy Transfer in MixingEnergy Transfer in Mixing
ProcessProcess Heat capacity Specific heat capacity
Energy transfer in mixingprocess
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Assume the temperature of body rises
Calculate heat capacity
Heat capacity
5.4 Specific heat capacity and energy transfer in mixing process (SB p.152)
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from T 1 to T 2 after it has absorbed anamount of energy E , the heat capacity of the body can be found by:
Heat capacity = Energy transfer
Temperature changes
i.e. C=E
T - T
Class Practice 2Class Practice 2
( )( ) T b h d d
5.4 Specific heat capacity and energy transfer in mixing process (SB p.152)
Heat capacity
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(a)(a) Two substances are heated under the same physical condition and their temperature changes against time are
plotted in the graph:
Substance A has a temperature change than substance B.Therefore, substance A has a heat capacity thansubstance B.
Answer
smaller
higher
Temperature / C
Time / s
s u b s
t a n c e
B
s u b s t a n c e A
Class Practice 2 (Contd)Class Practice 2 (
Contd)
Heat capacity
5.4 Specific heat capacity and energy transfer in mixing process (SB p.153)
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(b)(b) In a heating process, thetemperature of an object rises from 22C to 95 C. If the heat capacity of the
object is 900 J C -1 , of heat is absorbed by the object. Oncethe he
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