PRE-LABORATORY ASSIGNMENT
1. Define the index of refraction.
2. State the law of reflection. Use a diagram to define the angles involved.
3. State Snell's law. Define terms and angles using a diagram.
4. A light ray is incident on a plane interface between two media. The ray makes an incident angle with
the normal of 25.0° in a medium of n=1.25. What is the angle that the refracted ray makes with the
normal if the second medium has n=1.55? Show your work.
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5. A 60.0° prism has an index of refraction of 1.45 as shown below. A ray is incident as shown at an angle
of 60.0° to the normal of one of the prism faces. Trace the ray on through the prism and find the angles
02, 03, and 04 as defined in the laboratory instructions. Show your work.
60°
n = 1.00
n=1.00-
60°
n = 1.45
Physics Laboratory Manual · Loyd
40
LABORATORY
Reflection and Refraction
with the Ray Box
OBJECTIVES
Investigate for reflection from a plane surface, the dependence of the angle of reflection on the
angle of incidence.
Investigate refraction of rays from air into a transparent plastic medium.
Determine the index of refraction of a plastic prism from direct measurement of incident and
refracted angles of a light ray.
Investigate the focal properties of spherical reflecting and refracting surfaces.
.
EQUIPMENT LIST
Ray box, 60.0° prism, plano-convex lens, circular metal reflecting surfaces
Converging lens, diverging lens, protractor, straightedge, compass
Sharp hard-lead pencil, black tape, several sheets of white paper
.
.
THEORY
Reflection
The reflection of light from a plane surface is described by the law of reflection, which states that the
angle of incidence 0; is equal to the angle of reflection 0r.
The angles are measured with respect to a line perpendicular to the surface. Reflection from a plane
mirror or a plane piece of glass are examples of the law of reflection.
In Figure 40-1(a) several incident rays and reflected rays are shown for a plane surface. The angle of
incidence 0; is seen to be equal to the angle of reflection 0r.
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Refraction
In general, light rays incident on a plane interface will be partially reflected and partially transmitted into
the second medium. The transmitted ray undergoes a change in direction because the speed of light is
different for different media. The ray is said to be refracted. This is illustrated in Figure 40-1(b). The angle
of incidence is 01, and the angle of refraction is 02.
The speed of light in a vacuum is c (~3.00 x 108 m/s), the maximum possible speed of light. For any
material the speed of light is v where v Sc. A quantity called the index of refraction n for any medium is
THOMSON © 2008 Thomson Brooks/Cole, a part of The Thomson Corporation. Thomson, the Star logo, and Brooks/Cole are trademarks used herein under license. ALL RIGHTS RESERVED. No part of this work
- covered by the copyright hereon may be reproduced or used in any form or by any means—graphic, electronic, or mechanical, including photocopying, recording taping web distribution, information
storage and retrieval systems, or in any other manner—without the written permission of the publisher
BROOKS/COLE
401
10
COPYRIGHT © 2008 Thomson Brooks/Cole
Refraction
In general, light rays incident on a plane interface will be partially reflected and partially transmitted into
the second medium. The transmitted ray undergoes a change in direction because the speed of light is
different for different media. The ray is said to be refracted. This is illustrated in Figure 40-1(b). The angle
of incidence is 01, and the angle of refraction is 02.
The speed of light in a vacuum is c (~3.00 x 108 m/s), the maximum possible speed of light. For any
material the speed of light is v where v Sc. A quantity called the index of refraction n for any medium is
THOMSON © 2008 Thomson Brooks/Cole, a part of The Thomson Corporation Thomson, the Star logo, and Brooks/Cole are trademarks used herein under license. ALL RIGHTS RESERVED. No part of this work
- covered by the copyright hereon may be reproduced or used in any form or by any means—graphic, electronic, or mechanical, including photocopying, recording, taping, web distribution, information
BROOKS/COLE storage and retrieval systems, or in any other manner—without the written permission of the publisher
401
402
Physics Laboratory Manual Loyd
Reflection at Plane Surface
Refraction at Plane Surface
Reflecting Surface
n sin 01 = n2 sin 02
n2
02
Ray 1
Ray 1
n1/01)
Ray 2
Ray 2
Ray 3
Ray 3
Normal
to Surface
(a)
Normal
to Surface
(b)
Figure 40-1 Illustration of reflection and refraction of light rays at a plane surface.
defined by n=c/v. Because v sc, the only allowed values of n are n 2 1. The relationship (Snell's law)
between the angle of incidence 0, and the refracted angle 02 is
ni sin 01 = n2 sin 02
(Eq. 1)
When nj>n2, Equation 1 implies that 0,
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