Name:

Date:

Topic 3.4: How does light behave when it is reflected?

Concept 1 – Light is reflected in predictable patterns

Light rays follow a ________________________________ path, no matter what surface they reflect from.

The Laws of Reflection are three laws that describe the predictable path light follows when it strikes a reflective surface.

Ray diagrams can help you understand the laws of reflection.

· _______________________ ray: the light ray travelling towards the reflecting surface

· _______________________ ray: the light ray that has bounced off the reflecting surface

· ____________________: the line perpendicular to a surface, such as a mirror

· angle of ______________________ (i): the angle between the incident ray and the normal

· angle of ______________________ (r): the angle between the reflected ray and the normal

The Laws of Reflection

1. The angle of reflection (r) is ____________________ to the angle of incidence (i).

2. The reflected ray and the incident ray are on ____________________ sides of the normal.

3. The incident ray, the normal, and the reflected ray lie on the same _________________ (flat surface).

angle of

incidence

angle of

reflection

Concept 2 – Light reflected by a plane mirror produces an image that is nearly identical to the object

A ______________ ____________________ is an extremely smooth, flat reflective surface.

How an image forms in a plane mirror

· When light shines on an object (the tomato), it reflects off all points of the object in all

_____________________________.

· When these reflected rays reach the plane mirror, they follow the laws of reflection and reflect

__________________________.

· Some rays reach your eyes if you are looking at the mirror.

· They carry the ______________ pattern of light to the eye that was reflected off the object.

· Your brain assumes light travels in a ______________ ______________ and thinks the image is behind the mirror.

Characteristics of Images in Plane Mirrors

When you look at the image that forms in a plane mirror, it is:

· the same ___________ as the object

· the same _____________________ from the mirror as the object

· ___________________ (not upside-down)

· a ___________________ image (your brain imagines that it is behind the mirror)

· nearly identical to the object, but ________________________

Discussion Questions

1. What do the angle of reflection and the angle of incidence have in common? Consider how they are measured and how they compare to one another.

2. Why does an expert billiards (pool) player need to understand the laws of reflection to make an accurate shot?

3. Use a mirror to read the three messages below. Then answer the following questions.

a) Which of these images is a true reflection in a plane mirror?

b) How were the other images made?

c) Consider all of the letters of the alphabet. What capital letters look the same when they are reflected in a mirror?

Topic 3.5: How does light behave when it moves from one medium to another?

Concept 1 – Light changes direction and speed when it moves from one medium to another

Light travels in a ______________ ___________ through the same medium.

Light refracts (__________) when it travels from one medium to another (example: from air to water).

Refraction occurs because light travels at different

________________ in different media.

When light changes speed as it moves from one

medium to another, the _______________________ also changes.

The ______________________ of media determines if light waves slow down or speed up.

Light travels more ___________________ in a more dense medium than in a less dense medium.

air

water

air

water

When light travels from a less dense to a more dense medium (example: from air to water), the ray bends

___________________ the normal.

When light travels from a more dense medium to a less dense medium (example: from water to air), the ray

bends ___________________ from the normal.

Concept 2 – Light refracts as it passes through lenses

A lens is a transparent object that causes light to ______________________ and has at least one curved side.

Lenses come in different shapes, sizes and materials.

Lenses have two sides:

· either side can be plane (flat), concave (curved in), or convex (curved out)

· at least one side must be ______________________

There are two types of lenses:

___________________________ Lens

___________________________ Lens

· brings parallel light rays toward a common point

· have one or two curved surfaces

· ______________________ in centre

· rays ______________________ (come together) after passing through the lens

· spreads parallel light rays away from a common point

· have one or two curved surfaces

· ______________________ in centre

· rays ______________________ (spread out) as they leave the lens

Concept 3 – Refraction plays a role in human vision

_______________________ makes image formation in the eye possible.

· light travels in a ______________ ___________ from an object or source to the eye

· first travels through the ________________ (lens in front of the eye)

· travels from _____________ dense medium (air) to _____________ dense medium (cornea)

· path of light bends ________________ the normal

· light then passes through the lens

· lens also refracts light ________________ the normal

· lens is responsible for _______________________ on close objects

· light strikes the ______________ (a layer of cells that respond to light) at the back of the eye and forms an image

· cells in retina send nerve impulses to the brain through the ____________ _________

· brain interprets impulses as ______________

The human eye can focus on objects at different distances.

A circular muscle around the lens __________________ and __________________ to change the shape of the lens.

This allows the lens to refract light to a different extent and focus light from ____________

and __________________ objects on retina.

Discussion Questions

1. The textbook (p. 249) and slideshow (slides 7-9) use an analogy about a line of roller skaters to help explain refraction. Come up with another analogy that you could use to visualize how refraction occurs.

1. Use the image to help you explain why objects underwater seem closer to the surface than they actually are.

1. What characteristic makes one lens converging and another diverging?

1. Classify the following lenses as converging or diverging.

________________

________________

________________

________________

1. As a person ages, the lenses of the eyes become stiff. The muscle around the lenses can no longer make them change shape. How might this affect a person’s vision?

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