Download Solve the following problems using the intensity equation

Light and Optics Practice Problems
Solve the following problems using the Law of Reflection.
1. When we talk about angles of incidence and reflection, we often talk about the normal. The normal to a
surface is an imaginary line that is perpendicular to the surface. The normal line starts where the incident ray
strikes the mirror. A normal line is drawn for you in the sample problem above.
a. Draw a diagram that shows a mirror with a normal line and a ray of light hitting the mirror at an angle of
incidence of 60°.
b. In the diagram above, label the angle of reflection. How many degrees is this angle of reflection?
3. A ray of light strikes a mirror. The angle formed by the incident ray and the reflected ray measures 90°.
Sketch the picture before answering!! What are the measurements of the angle of incidence and the angle of
reflection?
4. In a basketball game, the ball is bounced (with no spin) toward a player at an angle of 40° to the normal.
What will the angle of reflection be? Draw a diagram that shows this play. Label the angles of incidence and
reflection and the normal.
The index of refraction (n) for a material is the ratio of the
speed of light in a vacuum to the speed of light in the material.
Index of refraction
= speed of light in a vacuum
speed of light in a material
Material
Vacuum
Air
Water
Glass
Diamond
Index of refraction (n)
1.0
1.0001
1.33
1.5
2.42
1. Could the index of refraction for a material ever be less than 1.0? Explain.
2. Explain why the index of refraction for air (a gas) is smaller than the index of refraction for a solid like glass.
3. Calculate the speed of light in water, glass, and diamond using the index of refraction and the speed of light
in a vacuum (3 × 108 m/sec).
4. When a light ray moves from water into air, does it slow down or speed up?
5. When a light ray moves from water into glass, does it slow down or speed up?
1. A light ray moves from water (n = 1.33) to a transparent plastic (polystyrene n = 1.59). Will the light ray
bend toward or away from the normal?
2. A light ray moves from sapphire (n = 1.77) to air (n = 1.0001). Does the light ray bend toward or away from
the normal?
3. Which light ray will be bent more, one moving from diamond (n = 2.42) to water (n = 1.33), or a ray moving
from sapphire (n = 1.77) to air (n = 1.0001)?
Ray Diagrams
2. Of the diagrams on the right, which one
correctly illustrates how a light ray enters and
exits a piece of thick glass? Explain your
answer.
3. In your own words, explain what happens to light as it enters glass from the air. Why does this happen? Use
the terms refraction and index of refraction in your answer.
4. Of the diagrams on the left, which one
correctly illustrates how parallel light rays
enter and exit a converging lens? Explain
your answer.
5. Draw a diagram of a converging lens that has a focal point of 10 centimeters. In your diagram, show three
parallel lines entering the lens and exiting the lens. Show the light rays passing through the focal point of the
lens. Be detailed in your diagram and provide labels.
1. A ray of light strikes a mirror. Which of the following rays (a, b, c, or d) best describes the path of the light
ray leaving the mirror?
6. A light ray crosses from a piece of glass into a liquid. You observe that the light ray bends closer to the
normal passing from the glass to the liquid. Based on this observation, how does the index of refraction for the
liquid compare to the index of refraction for the glass?
Reviewing Concepts
1. A light ray is an imaginary line that represents a thin beam of light in a ray diagram. Drawing light rays is
helpful in predicting the location and size of an image that will be created by a mirror or lens.
2. The image will appear as far behind the mirror as the object’s distance is in front of the mirror. For example,
if you are standing 1 meter in front of the mirror, the image will appear to be 1 meter behind the meter.
Therefore, the image will appear to be 2 meters away from the object.
3. Your mirror image is exactly the same size as you are.
4. (1) Transparency: light goes through matter almost unchanged.
(2) Translucency: light goes through matter but is scattered.
(3) Reflection: light bounces off matter.
(4) Absorption: light transfers its energy to matter.
Mirrored sunglasses reflect some of the light (the mirrored effect), absorb part of the light, and pass through part
of the light.
5. A transparent material passes light through such that you can see an image through it. A translucent material
scatters the light passing through it such that you cannot see an image through it.
6. At night, the smooth wet road surface causes specular reflection that shines the reflection of your headlights
back into your eyes. The dry road causes diffuse reflection and doesn’t shine back into your eyes.
7. Light is bent, or refracted, when it travels through a prism or a lens.
8. A line that is perpendicular to the surface.
9. The angle of incidence equals the angle of reflection.
10. The incident angle is the angle between the incident ray and the normal.
11. Light bends; refraction.
12. Glass has a greater ability to bend light toward the normal than ice because it has a larger index of
refraction.
13. Index of refraction. If the object and the material it is placed in have the same or similar indices of
refraction, the object will seem to disappear.
14. Total internal reflection occurs: (1) when the angle of incidence is greater than the critical angle, and (2)
when light is moving from one material into another with a lower index of refraction. Under these two
conditions, all the light reflects back into the material with the higher index of refraction rather than being
refracted by the material with the lower index of refraction.