What did the cosmic microwave background tell cosmologists about the early universe?
A) Nothing; it is a product of the black hole in the center of our own Galaxy.
B) The horizon problem, in that the microwave background is almost too isotropic
C) The discovery of dark energy and its role in accelerating the universe
D) The discovery of relativistic redshifts and the Big Bang
E) The dark matter in the universe is mostly baryonic in nature, for a closed Big Bang.
B
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A -4.0-?C charge is situated at the origin of an xy-coordinate system. What is the potential difference between a point x = 4.0 m and y = 2.0 m because of this charge?
A) -9.0 × 103 V B) 9.0 × 103 V C) -36 × 103 V D) 36 × 103 V E) 0 V
Suppose one twin takes a ride in a spaceship traveling at a very high speed to a distant star and then back again, while the other twin remains on Earth
Compared to the twin who remained on Earth, the astronaut twin is A) the same age as the Earth-twin. B) younger than the Earth-twin. C) older than the Earth-twin. D) The ages cannot be determined from the information provided.
Entropy: An irreversible engine operating between the temperatures of 550 K and 300 K extracts 1.20 kJ of heat from the hot reservoir and produces 0.450 kJ of work. How much entropy is created in the process?
A. 0.32 J/K B. 0.68 J/K C. 0.44 J/K D. 0.73 J/K E. 0 J/K
A solid state pulsed laser has an energy of 400 mJ per pulse. If its wavelength is 1.06 × 10^-6 m, how many photons are in each pulse?
a. 2 × 10^25 b. 2 × 10^21 c. 3 × 10^18 d. 6 × 10^38 e. 2 × 10^18