A 100-kW radio station emits EM waves in all directions from an antenna on top of a mountain. What is the intensity of the signal at a distance of 10 km?
a. 8 × 10^?5 W/m2
b. 8 × 10^?6 W/m2
c. 3 × 10^?3 W/m2
d. 0.8 W/m2
e. 2.5 × 10^?5 W/m2
a
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Absorption lines due to the interstellar medium indicate that some components of the interstellar medium are cold and of a very low density because
a. the lines are blue shifted. b. the lines are red shifted. c. the lines are extremely broad. d. the lines are extremely narrow. e. the lines are much darker than the stellar lines.
The reaction 2H + 2H ? 3H + 1H releases 4.03 MeV of energy. If one kilogram of deuterium were made to go through this reaction, how much energy would be produced?
A) 9.7 × 107 J B) 9.7 × 1013 J C) 1.9 × 107 J D) 1.9 × 1014 J E) 1.9 × 1011 J
Tripling the focal length of a telephoto lens, while holding aperture size constant, will change the light intensity admitted to the film by what factor?
a. 0.11 b. 0.33 c. 3.0 d. 9.0 e. 0.50
Replacing a wire resistor with another of the same material and length but with three times the diameter will have the effect of changing the resistance by what factor?
a. 1/3 b. 1/9 c. 3 d. 9