Properties of Light Review

© Michelle Brosseau, Mrs. Brosseau’s Binder

Properties of Light

© Mrs. Brosseau’s Binder

The Ray Model of Light
The lasers at this concert clearly show that
light travels in a straight line.

We will need to use this property to
understand how light interacts with
different surfaces.

Properties of Light

© Mrs. Brosseau’s Binder

The Ray Model of Light
We know that other light sources like
candles and light bulbs send light in all
directions.
We will use a light ray to represent the
direction of travel of the light.

Properties of Light

Lightbulb Image © KMJ/Wikimedia Commons, Laser Image © Marie Lan-Nguyen/Wikimedia Commons

Draw

Draw the light ray (s) that would come from the lightbulb.

Draw

Draw the light ray (s) that would come from the laser

© Mrs. Brosseau’s Binder

How Light Interacts with Surfaces
•

Some materials allow light to pass through
and other materials do not.
•

There are some materials that allow only
a fraction of the light to pass through.

•

Properties of Light

© Mrs. Brosseau’s Binder

Properties of Light

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Term: Transparent
Definition:When a material transmits all (or
almost all) incident light

Examples: glass, cling wrap

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Properties of Light

​

Term: Opaque
Definition: When a material does not transmit
incident light (it absorbs or reflects it)
Examples: wood, brick

© Mrs. Brosseau’s Binder

Properties of Light

​

Term: Translucent
Definition: When a material transmits some
incident light
Examples: frosted glass, waxed paper

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Flat Mirrors
When you stand in front of the mirror then
you are called the object and your reflection
is called the image.

Properties of Light

object
image

mirror

Match

Match the following

• transparent

• opaque

• translucent

you can see through water, air, and glass because light passes through these materials

matter does not allow light to pass through

an example is a sheet of waxed paper

• you can see through water, air, and glass because light passes through these materials

• matter does not allow light to pass through

• an example is a sheet of waxed paper

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Mirrors are created using a thin layer of
reflective silver or aluminum covered by a
protective sheet of glass.

Below is the scientific symbol for a mirror:

Properties of Light

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Here we can see the reflective and opaque sides of the mirror symbol in ray diagrams.

Properties of Light

Reflective surface

Opaque side

Open Ended

A one-way mirror is a special feature of police stations.  It is used for witnesses or officers to observe suspects without being seen themselves. 

How do you think a one-way mirror works?

Is it transparent, translucent or opaque?

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Think about it…
•

One-way mirrors are translucent and
operate by having one bright room and
one dark room.
•

Light reflects in the bright room and
transmits into the dark room.

Properties of Light

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Properties of Light

One-way mirror

Bright room

Dark room

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Properties of Light

One-way mirror

I see my
reflection

Bright room

Dark room

© Mrs. Brosseau’s Binder

Properties of Light

One-way mirror

Bright room

Dark room

I can’t see my
own reflection.
This room is too
dark. But I can
see into the next
room because
it’s bright.

I see my
reflection

© Mrs. Brosseau’s Binder

The Laws of Reflection
1.

Properties of Light

The angle of incidence equals the angle of
reflection

𝜃𝜃𝑖𝑖
𝜃𝜃𝑟𝑟

incident ray reflected ray

normal

𝜃𝜃𝑖𝑖 = 𝜃𝜃𝑟𝑟

© Mrs. Brosseau’s Binder

The Laws of Reflection
2.

Properties of Light

The incident ray, reflected ray and the
normal all lie in the same plane.

𝜃𝜃𝑖𝑖
𝜃𝜃𝑟𝑟

© Mrs. Brosseau’s Binder

Two Types of Reflections

Using the first law of reflection, we know that
when parallel light rays strike a surface they
all reflect at the same angle.
This is called specular reflection.

Properties of Light

Parallel
incident
rays

Parallel
reflected
rays

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Two Types of Reflections

When light strikes a surface that is not flat,
perhaps irregular or dull, the reflected rays
are sent out at different angles and do not
make a nice, clear image.
This is called diffuse reflection.

Properties of Light

Parallel
incident
rays

Non-parallel
reflected
rays

Multiple Choice

What type of reflection will this image produce?

• Regular Reflection

• Diffuse Reflection