In a pulsating variable star, which characteristic of the star changes dramatically with time?
A) mass
B) core temperature
C) luminosity
D) energy-generation process
E) rotation rate
C
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A metal airplane flies horizontally at 200. m/s where the Earth's magnetic field is vertical and is 45.0 ?T. If the wingspan is 25.0 meters:
(a) what emf is induced across the wings? (b) what wingspan would produce 1.0 volt emf? (c) The plane reverses direction. Does the polarity of the wingtip emf change, i.e., if the left wing was positive, does it now become negative?
A solar cell has a light-gathering area of 12.4 cm2 and produces 0.49 A at 0.93 V (dc) when illuminated with sunlight of intensity 884 W/m2 . What is the efficiency of the solar cell?
a. 42% b. 3.4% c. 64% d. 1.7% e. 19%
A vertical spring has a mass hanging from it, which is displaced from the equilibrium position and begins to oscillate. At what point does the system have the least potential energy?
A) at the highest point B) at one-fourth of the distance between the highest point and lowest point C) at the lowest point D) at the point where the spring is unstretched E) at the equilibrium point
How does an accretion disk around a neutron star differ from an accretion disk around a white dwarf?
A) The accretion disk around a neutron star is made mostly of helium while the accretion disk around a white dwarf is made mostly of hydrogen. B) The accretion disk around a neutron star is more likely to give birth to planets. C) The accretion disk around a neutron star is much hotter and emits higher-energy radiation. D) The accretion disk around a neutron star always contains much more mass.