A Carnot engine operating between reservoirs at 500°C and 300°C would have an efficiency of approximately
A. 0.30.
B. 0.50.
C. 0.67.
D. 0.74.
E. 0.11.
Answer: A
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If the population of a country doubles every 25 years, a 1980 population of 10 million will reach 80 million in the year
a. 2005. b. 2030. c. 2055. d. 2080. e. 2105.
Reactance: At what frequency does a 10-?F capacitor have a reactance of 0.12 k??
Fill in the blank(s) with the appropriate word(s).
Determine the total average hemispherical emissivity and the emissive power of a surface that has a spectral hemispherical emissivity of 0.8 at wavelengths less than 1.5 ?m. 0.6 at wavelengths from 1.5 to 2.5 ?m, and 0.4 at wavelengths longer than 2.5 ?m. The surface temperature is 1111 K.
GIVEN
• A surface at temperature (T) = 1111 K
• Spectral hemispherical emittance (??)
FIND
(a) The total average hemispherical emittance, ? (T)
(b) The emissive power, E(T)
SKETCH
PROPERTIES AND CONSTANTS
the Stephan-Boltzmann constant (?) = 5.67 × 10–8 W/(m2 K4)
Why can't a worldline on a spacetime diagram be horizontal?
A) A horizontal worldline corresponds to something moving infinitely fast. B) A horizontal worldline represents traveling backward in time. C) A horizontal worldline represents moving at exactly the speed of light. D) A horizontal worldline is possible. It corresponds to a constant, finite speed. E) A horizontal worldline is possible. It corresponds to a stationary object.