DELHI PUBLIC SCHOOL BANGALORE - EAST

PHYSICS LAB MANUAL

CLASS X [ 2021-2022]

TERM 1

INDEX

Guidelines to Write Records:

1. Use BLUE INK only.

2. Diagrams to be drawn in pencil. Geometry instruments to be used. No free hand diagrams.

3. Table borders to be drawn using ruler and pencil. Content to be written in pen.

4. Page borders to be drawn on blank page

5.Date of experiment, tabular column and result to be entered after experiment is done.

S.No Experiment Page.no Date Teacher’s

Signature

1A To determine focal length of a given concave mirror 1-2

1B To determine the focal length of a given convex lens 3-4

2 To trace the path of a ray of light passing through a

rectangular glass slab

5-7

3 To trace the path of the rays of light through a glass

prism

8-10

BLANK PAGE RULED PAGE

Diagram, Observation (tabular column etc), Calculations

Aim, Apparatus, Theory, Procedure, Result, Precautions

1

EXPERIMENT NO- 1(A)

AIM

To determine focal length of a given concave mirror by obtaining the image of a distant object.

APPARATUS REQUIRED

1. A concave mirror

2. A measuring scale

3. A screen holder

4. A mirror holder

5. A White screen

DIAGRAM

F

THEORY

• When a parallel beam of light coming from a distant object such as tree or pole, is

incident on the reflecting surface of a concave mirror, then after reflection they will meet

at a point, called principal focus (F).

• ‘f” is used to denote the distance between the pole P and the focus F of the concave

mirror.

PROCEDURE

1. Select the distant object such as a tree or pole or the sun.

2. Mount the concave mirror in a mirror holder.

3. Adjust the concave mirror in such a way that the rays of light coming from the tree fall on its

reflecting surface.

4. Obtain a well-defined and sharp image on a white wall of the laboratory by moving the mirror

backward or forward.

5. Measure the distance between the wall and the concave mirror with the help of a measuring

scale.

6. This will give approximate focal length of the mirror.

7. Repeat the experiments 2 times by selecting the different distant objects at different distances.

Record them in the observation table.

8. Find the mean value of the focal length for all the observations for different objects.

F

2

OBSERVATION TABLE

S.NO Distant

object

Position of

mirror A

(cm)

Position of

screen B

(cm)

Difference between

the position of the

screen and the

mirror (B-A)

(cm)

Focal length

F (cm)

1 f1=

2 f2=

3 f3=

CALCULATION

The mean value of the focal length F of concave mirror:

𝒇𝟏 + 𝒇𝟐 + 𝒇𝟑𝟑

= _______________𝒄𝒎

RESULT

The focal length of the concave mirror is _____________cm

According to the sign conventions the focal length of the concave mirror is = - cm

PRECAUTIONS

1. The polished surface of the concave mirror and the distinct object should be facing

each other.

2. The screen and the concave mirror stand should be parallel to the measuring scale. The

mirror holder along with the mirror should be perpendicular to the measuring scale.

***************************

3

EXPERIMENT NO- 1 (B)

AIM

To determine the focal length of a convex lens by obtaining the image of a distant object.

APPARATUS REQUIRED

1. A convex lens

2. A measuring scale

3. A screen holder

4. A lens holder

5. A White screen

DIAGRAM

THEORY

• The rays coming from a distant object such as tree/sun travelling a large distance, can be

considered as a parallel beam of light.

• These rays after refraction through the convex lens converge at a point called focus(F2 ).

• The distance between the lens (O) and the screen placed at the focus (F2) gives the

approximate focal length(f) of a convex lens.

PROCEDURE

1. Select a distant object such as a tree or a pole.

2. Mount the convex lens in the lens holder.

3. Keep the lens in a vertical position throughout the experiment.

4. Place the lens towards the selected distant object.

5. Keep a screen on the other side of the lens.

6. Move the lens forward and backward to get a sharp, real, and inverted image on

the screen.

7. Measure the distance between the lens and the screen with the help of a measuring

scale.

8. The distance between the screen and the convex lens gives the focal length of the

convex lens approximately.

9. Repeat the experiments 2 times by selecting the different distant objects at different

distances. Record them in the observation table.

10. Find the mean value of the focal length for all the observations for different objects.

4

OBSERVATION TABLE

S.No Distant

object

Position of

lens ‘L’ in

(cm)

Position of

screen M

(cm)

Difference between

the position of the

screen and lens (M-L)

(cm)

Focal length

F (cm)

1 f1=

2 f2=

3 f3=

CALCULATION

The mean value of the focal length F of convex lens:

𝒇𝟏 + 𝒇𝟐 + 𝒇𝟑𝟑

= _______________𝒄𝒎

RESULT

The approximate focal length of the convex lens is ------------------ cm.

According to the sign conventions the focal length of the convex lens is = + cm

PRECAUTIONS

1. While measuring the distance, meter scale should be kept horizontal and must be

parallel to the ground.

2. Distance should be measured only when well defined sharp image of the distant

object is obtained.

********************

5

EXPERIMENT NO -2

AIM

To trace the path of a ray of light passing through a rectangular glass slab for different angles of incidence.

Measure the angle of incidence, angle of refraction, angle of emergence, and interpret the result.

APPARATUS REQUIRED

1. A drawing board

2. 4-6 all pins

3. White sheet of paper

4. Rectangular glass slab

5. A protractor

6. A scale

7. A pencil

8. Thumb pins

DIAGRAM

THEORY

The refraction takes place at both air- glass interface and glass-air interface of a rectangular glass slab

i) When the light ray incidents on air- glass interface obliquely it bends towards the normal.

ii) The refracted ray incidents obliquely on the second parallel surface inside the rectangular glass slab

that is glass-air interface and after refraction it moves away from the normal.

These refractions at both the surfaces obey the laws of refraction.

6

PROCEDURE

1. Fix a white sheet on the soft drawing board using thumb pins.

2. Using a sharp pencil, draw the outline boundary of the glass slab, place it at the center of the

white paper.

3. Let ABCD be the rectangular figure obtained by drawing.

4. Mark point E on AB and draw a perpendicular EN and label it as a normal ray.

5. Draw one angle of 30° with the help of protractor with EN. Fix pins at P and Q at 4-5 cm on the

ray that is obtained by the angle.

6. Place the glass slab on the rectangular figure ABCD.

7. To fix R and S, see through the glass slab of side CD, such that when seen through the glass slab,

all the pins P, Q, R, and S should lie in a straight line.

8. Draw a small circle around the pins P, Q, R, and S and remove the pins.

9. Remove the glass slab.

10. Join points R and S such that it meets CD at point F. Draw a perpendicular N’M’ to CD at point F.

11. Using a pencil, join the points E and F.

12. Measure the angles formed at AB and CD, i.e, the incident angle, refracted angle, and emergent

angle.

13. The lateral displacement is obtained by extending the ray PQ in a dotted line which is parallel

ray to FS.

14. Measure the lateral displacement.

15. Repeat the same procedure for angle 45° and 60°.

OBSERVATION TABLE

S.No Angle of incidence

∠i =

Angle of refraction

∠r =

Angle of emergence

∠e =

∠i – ∠e

1 30°

2 45°

3 60°

7

RESULT

1. At the point of incidence the incident ray, refracted Ray and the normal to the air-glass interface, all

lie in the plane of paper

2. Within experimental limits the angle of emergence and the angle of incidence are equal.

3. The emergent ray is parallel to the incident ray.

4. Emergent ray is laterally displaced.

5. When the light ray travels from optically rarer medium to optically denser medium the angle of

refraction is less than the angle of incidence.

6. The refracted angle at the air-glass interface and the incident angle at the glass -air interface is found

to be equal.

7. From the observation table it is clear that with the increase in angle of incidence, angle of refraction

also increases.

PRECAUTIONS

1. Glass slab must be Clean and should be free from air bubble. The base of all the pins should be

placed in a straight line.

2. Keep your eyes around the plane of paper and in line while observing the image and fixing the

pins.

****************************

8

EXPERIMENT NO 3

AIM

To trace the path of the rays of light through a glass prism.

APPARATUS REQUIRED

• A white sheet

• Soft board

• Thumb pins

• 4-6 all pins

• Prism

• Pencil

• Scale

• Protractor

• Drawing board

DIAGRAM

EF- Incident ray

FG-Refracted ray

GH- Emergent ray

∠A – Angle of prism

∠i – Angle of incidence

∠r – Angle of refraction

∠e – Angle of emergence

∠δ – Angle of deviation.

THEORY

1. Let ABC be the principal section of a glass prism of refractive index ‘n’. The angle ‘A’ is the

refracting angle of the prism.

2. When a ray of light EF travels from rarer medium (such as air) is incident on a refracting surface

AB, it gets refracted and bends towards the normal to the plane of face AB. Here, ray of light is

entering from air to glass and refracted along FG.

3. At the second surface AC, the refracted light ray FG has entered from glass to air, i.e., denser to

rarer medium and emerges out, along GH as it has bent away from the normal i.e., bends towards

the base of prism shown in the diagram.

1 2

9

PROCEDURE

1. Take a sheet of white paper and fix it on the drawing board with the help of a drawing pins or

cello- tape.

2. Place a glass prism along its triangular base at middle on the paper. Mark the boundary ABC of

the glass prism and then remove the prism.

3. Draw a thin dotted line XY along one of the refracting surfaces (say AB) as shown in the figure

given below.

4. Draw a normal NFN1, i.e. perpendicular to line AB at F. Also, draw a line EF making an angle 30°

to the normal. EF will act as the incident ray.

5. Place the glass prism back to its original position ABC.

6. Fix two alpins P1 and Q1 on line EF vertically by gently pressing their heads with thumb into the

drawing board about 6 cm apart from each other.

7. Look the images of P1 and Q1 from the other refracting face AC. The images of pins P1 and

Q1 appear to be at I1 and I2.

8. Fix two more alpins P2 and Q2 vertically such that the feet of the pins P2 and Q2 appear to be on

the same straight line as the feet of the images I1 and I2 respectively. Confirm it by moving the

head slightly to either side while looking them. All the pins P2, Q2 and image of P1 and Q1 would

appear to move together if they are on the same straight line.

9. Remove the prism and all alpins. Mark the position of feet P2 and Q2 and P1 and Q1 [like ]

10. Join the pin pricks P2 and Q2 and produce P2Q2 so that it meets the refracting side AC of the prism

boundary at G. The line HG represents the path of the emergent ray.

11. Join F and G. The line FG represents the path of the refracted ray.

OBSERVATIONS

1. The ray of light entering from air to glass at the first refracting surface bends towards the normal

after refraction. At the second refracting surface, the ray of light entering from glass to air bends

away from the normal.

2. Thus, the ray of light suffers two refractions on passing through a prism and hence deviates

through a certain angle from its original path.

Angle of incidence

∠i =

Angle of refraction

∠r1=

Angle of emergence

∠e =

30°

RESULT

The line EFGH represents the path of light through the prism.

PRECAUTIONS

1. The refracting faces of the glass prism should be smooth, transparent and without any air bubble

or broken edge. It must be triangular.

10

2. The distance between the alpins should be at least 6 cm. Always adjust the feet and not the heads

of alpins to lie along the same straight line.

****************************