A transformer is to be used to step down voltage from an alternating current source from 220 V to 110 V. If the primary has 120 turns, then the number of turns in the secondary is
A. 2.
B. 720.
C. 1320.
D. 240.
E. 60.
Answer: E
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How does gravitational lensing tell us about the mass of a galaxy cluster?
A) Using Einstein's general theory of relativity, we can calculate the cluster's mass from the precise way in which it distorts the light of galaxies behind it. B) The lensing allows us to determine the orbital speeds of galaxies in the cluster, so that we can determine the mass of the cluster from the orbital velocity law. C) The lensing broadens spectral lines, and we can use the broadening to "weigh" the cluster. D) Newton's universal law of gravitation predicts how mass can distort light, so we can apply Newton's law to determine the mass of the cluster.
The basic biological structures of life on Earth are called
A) cells B) bacteria C) molecules D) atoms
Three loops of wire, one circular, one rectangular, and one square, are made from identical lengths of wire. If the loops are in the same increasing magnetic field perpendicular to the plane of the coils, which loop has the least induced emf?
a. the square one b. the rectangular one c. the circular one d. All three would have the same emf induced.
The principle of relativity is
A. momentum is conserved in all reference frames. B. the Earth is a noninertial reference frame. C. the speed of light is constant. D. the laws of physics are the same in all inertial reference frames. E. Newton's second law does not hold at high speeds.