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
Answer: A
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Of the following which might NOT vanish over one cycle of a cyclic process?
A. the work done by the substance minus the energy absorbed by the substance as heat B. the change in the pressure of the substance C. the energy absorbed by the substance as heat D. the change in the volume of the substance E. the change in the temperature of the substance
A 5000-kg freight car crashes into a 10,000-kg freight car at rest. They couple upon collision and move with a speed of 2 m/s. What was the initial speed of the 5000-kg freight car?
A) 4 m/s B) 5 m/s C) 6 m/s D) 8 m/s E) none of the above
Sirius, the brightest star in the sky, is 8.7 ly from the Sun. Determine Sirius' declination and right ascension
Find the average density of a white dwarf star if it has a mass equal to that of the Sun (2.0 × 10^30 kg) and a radius equal to that of the Earth (6.4 × 10^6 m)
a. 9.0 × 10^6 kg/m3 b. 1.8 × 10^7 kg/m3 c. 1.8 × 10^9 kg/m3 d. 3.6 × 10^10 kg/m3 e. 9.0 × 10^7 kg/m3