Download HWK 6

Physics 1230
Homework 6
Due Thursday. June 16, 2016
We are now studying how light rays behave when they encounter different materials.
They can reflect from surfaces (like they do at mirror surfaces or diffuse scattering
surfaces), be absorbed by the material (like black pavement on a sunny day), or can
transmit into and through the material (like light going through glass). When
transmitted, the light rays bend, which we call refraction. The rules for reflection
(reflected angle is equal to incident angle) and refraction (Snell’s Law) allow us to
predict how rays travel. The cases of spherical mirrors and lenses and how images are
formed are particularly useful.
1. Flat mirrors and ray tracing (6 points total)

Draw the image of the bird in the mirror. (2 points)

Indicate the reflected rays, where the rays appear to come from according to this
observer, and draw the bird image (clearly locate the top and bottom of the image
of the bird, and also make sure the ‘beak’ and the ‘tail’ are located in the correct
position, i.e. make sure the image of the bird is facing in the correct direction).
Indicate with numbers the order in which you drew each set of guidelines or rays.
Use a straight edge for all rays. (2 points)

Identify at least one location where the bird could be placed and the observer
would no longer see its reflection. (2 points)
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Physics 1230
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HW6.1
Summer 2016
Physics 1230
Homework 6
Due Thursday. June 16, 2016
2. Three different setups of eye, mirror, and object are shown in the figure. In
which of the setups can the eye NOT see a reflection of the object? Draw the
appropriate light rays on the figure to support your answer. You can either draw
on this assignment sheet and paste in to your written solutions, or trace the
pictures and draw on this. Label the angle of incidence and the angle
of reflection (and make sure they are equal). (6 points)
3. Light hits a slab of material straight on as shown
in the diagram. One finds that 40% of the
incident light is reflected and 40% is transmitted
all the way through the slab. What best describes
what happened to the other 20% of the light? (A
one-word answer.) (2 points)
Physics 1230
HW6.2
Summer 2016
Physics 1230
Homework 6
Due Thursday. June 16, 2016
4. Concave mirrors with objects far away from the focus. (5 points)
Use the space below to draw a picture of a concave mirror, its focal point, the optical
axis, and an arrow object ALL DRAWN TO SCALE USING A RULER. Then use
ray tracing to find the image of a 3 cm. high arrow in a concave mirror of focal length
3 cm., when the arrow is 8 cm in front of the mirror and points perpendicular to the
axis.
Answer the following questions by circling the answers: Is the image REAL or
VIRTUAL? Is the image UPRIGHT or INVERTED? Is the image LARGER or
SMALLER than the object?
5. Index of refraction calculations (4 points)
(a) The speed of light in a certain glass is 200,000 km/sec. What is the index of
refraction of this glass? Assume c = 300,000 km/s.
(b) Consider light entering the glass from part (a) or diamond (diamond has an
index of refraction of about 2.5) from air. This light will bend towards the
normal. Will it bend more strongly towards the normal in the diamond, or in
the glass?
Physics 1230
HW6.3
Summer 2016
Physics 1230
Homework 6
Due Thursday. June 16, 2016
6. Draw a sketch showing where you might see a rainbow in your lawn sprinkler in
the late afternoon. Show the position of the sun, the sprinkler, and you. (4 points)
7. The vengeful fish. (3 points)
A vengeful underwater fish is planning to poke a stick at a fisherman standing on the
shore. Should the fish push the stick ABOVE, BELOW, or DIRECTLY TOWARD
(circle one) where the fish sees the fisherman? Explain your answer below ane draw
a diagram that shows why your answer is correct. (3 points)
Physics 1230
HW6.4
Summer 2016