Why must radio telescopes have very large dishes?
A. A large mirror is necessary to resolve radio-emitting images.
B. The large dish is to compensate for atmospheric absorption of radio waves.
C. Large radio telescopes are easier to repair than small instruments.
D. Radio-emitting objects are very far from Earth, and so are very dim.
E. Size is immaterial to quality observations.
Answer: A
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A +4.0-?C charge is placed on the x axis at x = +3.0 m, and a ?2.0-?C charge is located on the y axis at y = ?1.0 m. Point A is on the y axis at y = +4.0 m. Determine the electric potential at point A (relative to zero at the origin)
a. 6.0 kV b. 8.4 kV c. 9.6 kV d. 4.8 kV e. 3.6 kV
A wire has a cross-sectional area of 0.10 mm2. If there are 4.0 × 1028 atoms per cubic meter in this wire, and if each atom contributes 2 free electrons, what is the drift velocity of the electrons when the current in the wire is 6.0 A?
(e = 1.60 × 10-19 C) A) 0.0047 m/s B) 0.0092 m/s C) 0.94 m/s D) 0.019 m/s
If light from a distant star passes close to a massive body, the light beam will
A) bend towards the star due to gravity. B) continue moving in a straight line. C) change color to a shorter wavelength. D) slow down. E) accelerate due to gravity.
Why do we say that the Doppler technique gives the planet's "minimum mass"?
A) The size of the Doppler shift that we detect depends on whether the planet's orbit is tilted. B) The size of the Doppler shift that we detect depends on knowing the star's mass, which can be very uncertain. C) Extrasolar planets are always increasing in mass. D) Doppler measurements are very difficult, producing noisy data that often cause astronomers to underestimate a planet's mass.