# The Nature of Light and the Laws of Geometric OpticsPage 3

#### WATCH ALL SLIDES

d is the distance between the wheel and the mirror.

Δt is the time for one round trip.

Then c = 2d / Δt

Fizeau found a value of

c = 3.1 x 108 m/s.

Section 35.2

Slide 14

## The Ray Approximation in Ray Optics

Ray optics (sometimes called geometric optics) involves the study of the propagation of light.

It uses the assumption that light travels in a straight-line path in a uniform medium and changes its direction when it meets the surface of a different medium or if the optical properties of the medium are nonuniform.

The ray approximation is used to represent beams of light.

Section 35.3

Slide 15

## Ray Approximation

The rays are straight lines perpendicular to the wave fronts.

With the ray approximation, we assume that a wave moving through a medium travels in a straight line in the direction of its rays.

Section 35.3

Slide 16

## Ray Approximation, cont.

If a wave meets a barrier, with λ<<d, the wave emerging from the opening continues to move in a straight line.

d is the diameter of the opening.

There may be some small edge effects.

This approximation is good for the study of mirrors, lenses, prisms, etc.

Other effects occur for openings of other sizes.

See fig. 35.4 b and c

Section 35.3

Slide 17

## Reflection of Light

A ray of light, the incident ray, travels in a medium.

When it encounters a boundary with a second medium, part of the incident ray is reflected back into the first medium.

This means it is directed backward into the first medium.

For light waves traveling in three-dimensional space, the reflected light can be in directions different from the direction of the incident rays.

Section 35.4

Slide 18

## Specular Reflection

Specular reflection is reflection from a smooth surface.

The reflected rays are parallel to each other.

All reflection in this text is assumed to be specular.

Section 35.4

Slide 19

## Diffuse Reflection

Diffuse reflection is reflection from a rough surface.

The reflected rays travel in a variety of directions.

A surface behaves as a smooth surface as long as the surface variations are much smaller than the wavelength of the light.

Section 35.4

Slide 20

## Law of Reflection

The normal is a line perpendicular to the surface.

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