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Unit IV: Refraction Review
The Speed of Light
1) The star Sirius is 8.7 light years away. What does this mean? (8.7 years)
2) How long would it take a phone call to reach Mars? Earth and Mars are 8.0 x 1010 m apart. (270 s)
3) The international space station has an orbit 278 km above the Earth’s surface. If they are watching live
T.V. in the station, how long is their delay? Assume their T.V. signal is sent via radio waves. (0.000927 s)
4) How many parsecs away is a galaxy if it takes 5.00 x 1010 s to reach us? Find this distance in meters first.
(486 pc)
5) How many astronomical units away from Earth is the planet Jupiter if it takes sunlight 2594 s to reach it?
(5.19 AU)
Refraction
1) What is the speed of light in water? (2.26 x 108 m/s)
2) The speed of light is measured at 2.19 x 108 m/s. What substance is the light travelling in? (Ethyl
Alcohol)
3) In the diagram below, label the angle of incidence, angle of reflection, angle of refraction, normal, the
incident light ray, the refracted light ray, and the interface.
4) A beam of light from carbon tetrachloride enters oleic acid. If the angle of incidence is 86°, what is the
angle of refraction? (86°)
5) An unknown substance has an incident ray of light with an angle of 26.0°. If the angle of refraction in
crown glass is 24.4°, what is the unknown substance? (Antifreeze)
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6) Trace the light through the substances.
7) Light travels from zircon into fused quartz. What is the critical angle? (49.5°)
Photometry
1) A bulb has a luminous flux of 2400 lm. Determine the illuminance of a book that is 1.50 m away from the
light source. (85 lx)
2) How far away is an object from a light source if a 2850 lm bulb gives the object an illumination of 45.0
lx? (2.24 m)
3) A street lamp with a luminous intensity of 510 cd is placed 7.00 m above the ground. Find the luminous
flux and the illuminance at the ground. (1.0 x 101 lx, 6400 lm)
4) A 35.0 cd source placed 2.00 m from a light meter gives the same illumination as an unknown source
placed 4.25 m from the meter. Determine the intensity of the unknown source. (158 cd)
Things and Thoughts
1) From your table, in which material is the speed of the light the greatest? The least?
2) What happens when the incident angle is equal to the critical angle for two substances? What happens
if the incident angle is greater than the critical angle? Less than?
3) When calculating the speed of light in a medium, what number should you never exceed?
4) State the two laws of refraction.
5) If going from a less refractive to more refractive substance, which way does the refracted ray bend?
What about from more refractive to less refractive?
6) Explain the difference between hunting fish from above water with spear and with a laser gun.
7) Explain an application of refraction.
8) Explain an application of total internal reflection.