A collection of atoms has 20% of the sample in a state above the ground state. If these emit coherent radiation, what is the wavelength of the laser light produced? (c = 3.00 × 108 m/s, h = 6.626 × 10-34 J ? s, 1 eV = 1.60 × 10-19 J)
A) 210 nm
B) 91 nm
C) 340 nm
D) 34 nm
Answer: A
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A brass rod, 75.0 cm long and having a cross-sectional area of 2.50 cm2, conducts heat from a large furnace at 375°C into a very large cold water bath at 10.0°C
without losing any heat at the lateral surface of the rod. Steady state has been established, and the thermal conductivity of brass is 109 W/m?K. The rate at which the entropy of the system (furnace plus water) is changing is closest to A) 2.05 × 10-2 W/K. B) 2.64 × 10-2 W/K. C) 3.54 × 10-2 W/K. D) 4.69 × 10-2 W/K. E) 6.74 × 10-2 W/K.
The basic mechanism for plate movement is thought to be
a. earthquake surface waves. b. the tidal force of the Moon. c. convection cells in the asthenosphere. d. earthquake body waves.
If the magnification of a mirror or lens is negative, it means that
A) the image is smaller than the object. B) the image is inverted and smaller than the object. C) the image is inverted. D) the object is farther from the mirror (or lens) than the image. E) the image is farther from the mirror (or lens) than the object.
If the same-sized force is made to act over a smaller area, the pressure is
a. decreased b. increased c. unchanged d. dependent upon the shape of the area