All of the following observations are real. Which one does not support the model in which active galactic nuclei are powered by accretion disks around massive black holes?
A) The most luminous active galactic nuclei have huge redshifts.
B) X-ray emission from active galactic nuclei can vary significantly in times as short as a few days.
C) The total luminosity of an active galactic nucleus can be as high as about 10 billion times that of the Sun.
D) Spectra of active galactic nuclei show that clouds of gas are orbiting a central object at a high speed.
A) The most luminous active galactic nuclei have huge redshifts.
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An AC series circuit contains a resistor of 20 W, an inductor of 50 mH, and a variable capacitor. If the frequency of the applied voltage is 500 Hz, to what setting should the capacitor be set if resonance is achieved?
a. 2.4 µF c. 2.0 µF b. 3.4 µF d. 0.8 µF
Determine the number of air masses through which the sun’s rays must pass to reach the earth at the equator and at the equinox.
What will be an ideal response?
A skier is pulled by a tow rope up a frictionless ski slope that makes an angle of 12° with the horizontal. The rope moves parallel to the slope with a constant speed of 1.0 m/s. The force of the rope does 900 J of work on the skier as the skier moves a distance of 8.0 m up the incline.
(a) If the rope moved with a constant speed of 2.0 m/s, how much work would the force of the rope do on the skier as the skier moved a distance of 8.0 m up the incline? At what rate is the force of the rope doing work on the skier when the rope moves with a speed of (b) 1.0 m/s and (c) 2.0 m/s?
Which of the following choices is an appropriate unit for measuring entropy changes?
a. J • K c. J/s b. N • K d. J/K