In 1983 the standard meter was redefined to what it is currently. What was the previous definition from 1960 based on?
a. specific alloy bar housed at Sevres, France
b. wavelength of light emitted by certain krypton atoms
c. distance from the Earth's equator to the North Pole
d. the distance light travels in a certain fraction of a second
b
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AC Generator: A rectangular coil of N turns, length L = 25 cm, and width w = 15 cm, as shown in the figure, is rotating in a magnetic field of 1.6 T with a frequency of 75 Hz. If the coil develops a maximum emf 56.9 V, what is the value of N?
A. 2 B. 4 C. 6 D. 8 E. 10
An object 2.0 cm in height is placed at the center of curvature C in front of a concave mirror. What is the height of its image?
A) -0.50 cm B) -1.0 cm C) -1.5 cm D) -2.0 cm E) -6 cm
Recent evidence suggests that Mars once had a global magnetic field. Assuming this is true, which of the following could explain why Mars today lacks a global magnetic field like that of Earth?
A) Mars rotates much slower than the Earth. B) The Martian core is made of rock, while Earth's core is made of metal. C) Mars's interior has cooled so much its molten core layer no longer undergoes convection. D) Mars is too far from the Sun to have a global magnetic field.
Approximately how many extrasolar planets have been discovered to date?
A) tens B) hundreds C) thousands D) millions E) billions