How does solar luminosity vary during the sunspot cycle?
What will be an ideal response?
The Sun is slightly more luminous at periods of sunspot maximum than at sunspot minimum.
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Two concentric spheres 0.2 m and 0.3-m in diameter, with the space between them evacuated, are to be used to store liquid air (133 K). If the surfaces of the spheres have been flashed with aluminum and the liquid air has a talent heat of vaporization of 209 kJ/kg, determine the number of kilograms of liquid air evaporated per hour.
GIVEN
? Two concentric spheres with the space between them evacuated and liquid air in the inner sphere
? Diameters
? D1 = 0.2 m
? D2 = 0.3 m
? Liquid air temperature (Ta) = 133 K
? Room temperature (T?) = 293 K
? Surfaces of the spheres have been flashed with aluminum
? Heat of vaporization of liquid air (hfg) = 209 kJ/kg = 209,000 J/kg
FIND
? The number of kilograms of liquid air evaporated per hour ( m )
ASSUMPTIONS
? Steady state
? Convective thermal resistance between the liquid air and interior sphere is negligible
? Thermal resistance of the sphere walls is negligible
? Natural convection on the exterior is negligible
? The room behaves as a blackbody enclosure
? The thickness of the sphere walls in negligible
SKETCH
PROPERTIES AND CONSTANTS
From Appendix 1, Table 5, the Stephan-Boltzmann constant
From Table 11.3, the hemispherical emissivity of the spheres will be approximated by that for
oxidized aluminum at 310 K: ? ? = ??1 ???2 = 0.11
If a = 2.0 cm, b = 5.0 cm, and I = 20 A, what is the magnitude of the magnetic field at the point P?
A. 4.5 ?T B. 7.5 ?T C. 9.0 ?T D. 6.0 ?T E. 3.6 ?T
A radioactive isotope of atomic number Z emits a beta-minus particle, and then the daughter nucleus emits a gamma ray. What is the atomic number of the resulting nucleus after both processes?
A) Z - 3 B) Z + 1 C) Z - 2 D) Z - 1
A binary system that looks like the one depicted in this painting should shine brightly in x-rays. Which one of the four labeled regions is the source of most of the x-rays?
A) Region I B) Region II C) Region III D) Region IV