At every instant the ratio of the magnitude of the electric to the magnetic field in an electromagnetic wave in vacuum is equal to
A. the speed of radio waves.
B. the speed of light.
C. the speed of gamma rays.
D. all of the above.
E. only (a) and (b) above.
Answer: D
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A. Mercury B. Venus C. Mars D. Earth E. All of them have craters.
Auroras near the poles of the planets
a. are found on Earth. b. are found on Jupiter. c. indicate the presence of a magnetic field. d. occur when particles in the solar wind hit a planet’s atmosphere. e. all of the above.
The main source of energy for a star as it grows in size to become a red giant is
A) hydrogen fusion in the central core. B) helium fusion in the central core. C) hydrogen fusion in a shell surrounding the central core. D) gravitational contraction.
If it is midnight in New York, it is
A) daytime in Sydney, Australia. B) midnight in Sydney, Australia. C) midnight in Los Angeles. D) midday in Rio de Janeiro, Brazil. E) midnight everywhere.