Light and OpticsTopic 2: Reflection
Vocab!
• Transparent – light rays go through it
• Translucent – some light rays go through it, some get reflected or absorbed
• Opaque – light rays get reflected or absorbed
The Ray Model of Light
• The ray model of light is a way of using arrows, lines or rays to show how light acts.
• The ray model tells us that light travels in straight lines.
• Light rays do not bend around an object, they either hit the object OR they go right past it in a straight line.
How do shadows prove the ray
model?
• A shadow has sharp edges because the light does not bend around the object.
• A shadow is at least the same size (or bigger) than the object.
• A shadow's size changes in a predictable way:– the shadow gets bigger as the object moves towards
the light source
The Ray Model of Light
Reflection• Reflection is when light strikes a surface then bounces off
that surface
Law of Reflection
• The law of reflection states that the angle of
reflection will always equal the angle of
incidence for a ray of light that is reflecting off
of a surface
• In other words, when a ray of light strikes a
reflective surface such as a mirror, the light will
bounce back from that surface at the same angle
that it hit the surface.
Reflection diagram
Reflective surface (mirror)
This imaginary line is called the "normal" line = n
(90 degrees from mirror line)
n
Incident ray "I"Angle of incidence
“ i ”
i
Reflec
ted ra
y "R"
r
Angle of reflection
“ r ”
Reflection Diagram
Is the Law of Reflection Always
True?
Why can you see yourself in a mirror or a highly
polished surface such as a window but not see
yourself in the dirt?
A
“smooth”
piece of
paper
Is the Law of Reflection always
true? YES!!
Normal line is different for each ray.
Normal line is the same for each ray.
• The answer is yes! The only difference with a
rough surface is that the normal line will be
different for each ray of light.
• Therefore, despite the fact that each of the rays
How do we see a reflected image in a
mirror?
• Light rays coming from a light source reflect
off of an object and towards the mirror.
• These rays then travel from the mirror to your
eyes in a straight line.
• Since your brain thinks that the rays are
coming from the mirror, it looks like the object
is inside of the mirror!
Regular Reflection
• smooth surfaces allow incoming rays to bounce
off as parallel rays (regular reflection)
• the shinier and smoother the surface, the better the
reflection
Label the diagrams of types of
beams.
divergingdiverging parallelparallel convergingconverging
Curved Mirrors
Concave Mirrors Convex Mirrors
Concave Mirrors
• curve inwards
• reflect light inwards to a central point in front of the mirror.
• reflect light from a small area
• when you are close to the mirror: images are larger/closer (magnified)
• when you are far from the mirror: images are inverted and smaller/farther away
• Example: make-up mirrors.
What is happening?
Convex Mirrors
• curve outward
• reflect light outward away from the outer
edges of the mirror
• reflect light from a large area
• images are smaller/further away but never
inverted
• Example: security mirrors, car mirrors
What is happening?
Concave up
close.
(Not inverted)
(Magnified)
Convex.
(Not Inverted)
(Smaller/farther
away)
Concave from
far away.
(Inverted)
Review