The tungsten filament of a light bulb has an operating temperature of about 2 050 K. If the emitting area of the filament is 0.70 cm2, and its emissivity is 0.68, what is the power output of the light bulb? (? = 5.67 × 10^?8 W/m2/K4)
a. 70.1 W
b. 47.7 W
c. 477 W
d. 42.7 W
e. 39.7 W
b
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The radiant is the common point from which ________ seem(s) to diverge.
A. meteorites B. asteroids C. comets D. a meteor shower
How does the theory of inflation explain the near-uniformity of the cosmic microwave background?
A) Prior to rapid inflation, all regions of space were close enough to bounce radiation back-and-forth and reach the same temperature. B) Matter expanded into regions of space that had no matter, and thus ended up at the same temperature. C) The expanding universe would have cooled. D) Matter was near the critical-density for a universal collapse, which smoothed out the differences in temperatures.
A thin-walled cylindrical tank with a diameter of 2.0 m and wall thickness of 18 mm is open at the top. The height h of water (weight density 5 9.81 kN/m3) in the tank at which the circumferential stress reaches 10 MPa in the tank wall is approximately:
(A) 14 m
(B) 18 m
(C) 20 m
(D) 24 m
What is the stratosphere?
A) the lowest layer in the atmosphere B) the part of the atmosphere that absorbs optical light C) the part of the atmosphere that absorbs ultraviolet D) the part of the atmosphere that absorbs X-rays E) the highest layer in the atmosphere