# The Nature of Light and the Laws of Geometric OpticsPage 4

#### WATCH ALL SLIDES

It is at the point where the incident ray strikes the surface.

The incident ray makes an angle of θ1 with the normal.

The reflected ray makes an angle of θ1’ with the normal.

Section 35.4

Slide 21

## Law of Reflection, cont.

The angle of reflection is equal to the angle of incidence.

θ1’= θ1

This relationship is called the Law of Reflection.

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

Because this situation happens often, an analysis model, wave under reflection, is identified.

Notation note:

The subscript 1 refers to parameters for the light in the first medium.

If light travels in another medium, the subscript 2 will be associated with the new medium.

Since reflection of waves is a common phenomena, we identify an analysis model for this situation, the wave under reflection analysis model.

Section 35.4

Slide 22

## Multiple Reflections

The incident ray strikes the first mirror.

The reflected ray is directed toward the second mirror.

There is a second reflection from the second mirror.

Apply the Law of Reflection and some geometry to determine information about the rays.

Section 35.4

Slide 23

## Retroreflection

Assume the angle between two mirrors is 90o .

The reflected beam returns to the source parallel to its original path.

This phenomenon is called retroreflection.

Applications include:

Measuring the distance to the Moon

Automobile taillights

Traffic signs

Section 35.4

Slide 24

## Refraction of Light

When a ray of light traveling through a transparent medium encounters a boundary leading into another transparent medium, part of the energy is reflected and part enters the second medium.

The ray that enters the second medium changes its direction of propagation at the boundary.

This bending of the ray is called refraction.

Section 35.5

Slide 25

## Refraction, cont.

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

The angle of refraction depends upon the material and the angle of incidence.

v1 is the speed of the light in the first medium and v2 is its speed in the second.

Section 35.5

Slide 26

## Refraction of Light, final

The path of the light through the refracting surface is reversible.

For example, a ray travels from A to B.

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