The universe first became transparent to most light, coinciding with the origin of the cosmic background radiation, when the universe cooled enough to allow the formation of
A) atomic nuclei. B) stars and galaxies.
C) neutral atoms. D) protons and neutrons.
A) 8.7 keV B) 7.8 keV C) 7.8 MeV D) 3.7 MeV E) 8.7 MeV
C
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A boat moves at 11.0 m/s relative to the water. If the boat is in a river where the current is 2.00 m/s, how long does it take the boat to make a complete round trip of 1000 m upstream followed by a 1000 m trip downstream?
a. 188 s c. 208 s b. 205 s d. 222 s
A Van de Graaff generator has a spherical dome of radius 12 cm. Operating in dry air, where "atmospheric breakdown" is at Emax = 3.0 × 10^6 N/C, what is the maximum charge that can be held on the dome? (ke = 8.99 × 10^9 N×m2/C2)
a. 4.8 × 10^-6 C c. 2.7 × 10^-5 C b. 1.3 × 10^-5 C d. 3.3 × 10^-6 C
A rectangular wire loop (length = 60 cm, width = 40 cm) lies completely within a perpendicular and uniform magnetic field of magnitude of 0.5 T. If the length of the loop starts increasing at a rate of 20 mm/s at time t = 0, while the width is decreasing at the same rate, what is the magnitude of the induced emf at time t = 4.0 s?
a. 6.8 mV b. 5.2 mV c. 3.6 mV d. 8.4 mV e. 10 mV
When a sample of water at 0.0°C is cooled to -36.0°C and freezes in the process, 935,000 kJ of heat is liberated
What is the mass of this sample of water? For water LF = 334,000 J/kg, LV = 2.256 × 106 J/kg, and the specific heat of ice is 2050 J/kg ? °C. A) 2290 kg B) 1145 kg C) 2800 kg D) 12,700 kg