Power: In the circuit shown in the figure, the 60-Hz ac source has a voltage amplitude of 120 V, the capacitive reactance is 850 ?, and the inductive reactance is 340 ?. What is the resistance R if the power factor is 0.80?
A. 680 ?
B. 610 ?
C. 540 ?
D. 460 ?
E. 380 ?
Answer: A
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An enclosed chamber with sound absorbing walls has a 2.0 m × 1.0 m opening for an outside window. A loudspeaker is located outdoors,, 78 m away and facing the window
The intensity level of the sound entering the window space from the loudspeaker is 79 dB. Assume the acoustic output of the loudspeaker is uniform in all directions and that the acoustic energy incident upon the ground is completely absorbed and therefore is not reflected into the window. The threshold of hearing is 1.0 × 10-12 W/m2. The acoustic power entering through the window space is closest to A) 160 µW. B) 79 µW. C) 320 µW. D) 790 µW. E) 1600 µW.
A Hertzsprung-Russell diagram shows stars on a plot of
A) luminosity vs. distance. B) magnitude vs. apparent brightness. C) apparent brightness vs. temperature. D) luminosity vs. temperature.
Opacity is
a. the balance between the pressure and force of gravity inside a star. b. the force that binds protons and neutrons together to form a nucleus. c. the force that binds an electron to the nucleus in an atom. d. a measure of the resistance to the flow of radiation (photons) through a gas. e. the temperature and density at which a gas will undergo thermonuclear fusion.
Radiation darkening explains why
A) there are so many dark craters on the jovian moons. B) Uranus' moons are darker than Saturn's. C) Earth's Moon is made of rock, but jovian moons are icy. D) Iapetus has a two-faced appearance.