Page 400 - Schaum's Outline of Theory and Problems of Applied Physics

CHAP. 30] LIGHT 385

30.5. What is the frequency of radio waves whose wavelength is 20 m?

30.6. A certain radio station transmits at a frequency of 1050 kHz. What is the wavelength of these waves?
30.7. A 100-W tungsten-filament lamp has a luminous efficiency of 16 lm/W. Find its intensity in candelas.

30.8. A newspaper is held 20 ft from a 2000-cd street lamp at midnight. What is the maximum illumination of the
newspaper?
30.9. A 150-cd lamp is to be substituted for a 100-cd lamp over a workbench. If the original lamp was 2 m above the
workbench, how much higher can the new lamp be and still provide the same illumination?
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30.10. Find the solid angle subtended at the center of a sphere of radius 2.0 m by an area of 50 cm on its surface.
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30.11. An illumination of 10 lx is produced on a screen by a projector 6 m away. Find the luminous intensity of the
projector looking into its beam.
30.12. What intensity should a lamp have if it is to provide an illumination of 400 lx at a distance of 3 m on a surface whose
normal is 20 from the direction of the light rays?
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30.13. A playing field 250 ft by 400 ft is to have an average illumination at night of 30 ft. How many 4000-cd lamps are
needed if reflectors are used that enable 40 percent of their luminous flux to reach the field?
30.14. The index of refraction of benzene is 1.50. Find the velocity of light in benzene.

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30.15. The velocity of light in ice is 2.3 × 10 m/s. What is its index of refraction?
30.16. A beam of light enters a plate of flint glass (n = 1.63) at an angle of incidence of 40 . Find the angle of
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refraction.
30.17. A beam of light enters a tank of glycerin at an angle of incidence of 45 . The angle of refraction is 29 . Find the
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index of refraction of glycerin.
30.18. Find the critical angle for total internal reflection for light going from ice (n = 1.31) into air.

30.19. A stick frozen into a pond in winter appears to be 3 cm below the surface. What is its actual depth in the ice?

Answers to Multiple-Choice Questions

30.1. (c) 30.8. (a)
30.2. (d) 30.9. (c)

30.3. (c) 30.10. (a)

30.4. (a) 30.11. (a)

30.5. (d) 30.12. (c)
30.6. (c) 30.13. (c)

30.7. (c) 30.14. (c)