A light beam from a 2.1-mW He-Ne laser has a wavelength of 633 nm. How many photons does the laser emit in one second? (h = 6.626 × 10-34 J • s, c = 3.00 × 108 m/s)
A) 6.7 × 1015
B) 8.8 × 1015
C) 1.1 × 1016
D) 1.3 × 1016
A
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Which of the following years had the least sunspot activity?
A) 1930 B) 1949 C) 1961 D) 1987
Which situation has the least magnitude of angular momentum about the origin?
A. A 2 kg mass travels along the line y = 3 m with speed 1.5 m/s. B. A 1 kg mass travels in a circle of r = 4.5 m about the origin with speed 2 m/s. C. A disk with I = 3 kg·m2 rotates about its center (on origin) with ? = 3 rad/s.
1.A 2.B 3.C 4.Both A and B 5.Both A and C 6.Both B and C 7.All have the same magnitude angular momentumAssume electrons are accelerated through a potential difference of 25 000 V inside a TV picture tube. What is the minimum wavelength that could be produced when the electrons strike the phosphor? (1 Å = 10-10 m)
a. 0.50 Å b. 1.0 Å c. 10 Å d. 100 Å e. 0.25 Å
The distinguishing feature of a starburst galaxy is
A) the presence of an unusually large number of binary star systems containing X-ray bursters. B) a very large luminosity compared to the total luminosity of the Milky Way. C) strong radio emission from "lobes" of material well outside the visible boundaries of the galaxy. D) a rate of star formation that may be 100 or more times greater than that in the Milky Way.