A total shadow is called
A) an umbra, and a partial shadow a penumbra.
B) a penumbra, and a partial shadow an umbra.
C) neither of these
Answer: A
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The supermassive black hole at the center of the galaxy is:
A.) 15 light-years away. B.) 300 light-years away. C.) 8,800 light-years away. D.) 26,000 light-years away. E.) 90,000 light-years away.
________ galaxies may contain a few million to few trillion solar masses.
A. Spiral B. Independent of their type C. Irregular D. Elliptical
The power output, Pout, of an ideal step-up transformer that receives power input, Pin, and which has N1 turns in the primary and N2 turns in the secondary coil is given by
A.
B.
Pin.C.
Pin.D.
Pin.E.
Pin.A spherical satellite circling the sun is to be maintained at a temperature of 25°C. The satellite rotates continuously and is covered partly with solar cells having a gray surface with an absorptivity of 0.1. The rest of the sphere is to be covered by a special coating which has an absorptivity of 0.8 for solar radiation and an emissivity of 0.2 for the emitted radiation. Estimate the portion of the surface of the sphere which can be covered by solar cells. The solar irradiation may be assumed to be 1,420 W/m2 of surface perpendicular to the rays of the sun.
GIVEN
- A spherical satellite partially covered with solar cells is orbiting the sun
- Satellite temperature (Ts) = 25°C = 298 K
- Solar cell absorptivity (?c) = 0.1
- Absorptivity of the rest of the satellite (?2s) = 0.8
- Emissivity of the rest of the satellite (?s) = 0.2
FIND
The portion of the surface which can be covered by solar cells
ASSUMPTIONS
Ambient temperature (T?) = 0 K
Quasi steady state
Solar irradiation (Iso1) = 1420 W/m2 of the surface perpendicular to the rays of the sun
Satellite and cell surfaces are gray
Surface temperature of the satellite is uniform
SKETCH
PROPERTIES AND CONSTANTS
the Stephan-Boltzmann constant
