Compared to the distance between Earth and Mars, the distance between Jupiter and Saturn is
A) much larger.
B) about the same.
C) much smaller.
D) just slightly less.
A) much larger.
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Millisecond pulsars that are very old are
a. believed to be the result of mass transfer from a companion that increased the spin of the pulsar. b. all single objects. c. not spinning as rapidly as they seem because they have four hot spots that produce the flashes. d. X-ray binaries. e. gamma-ray bursters.
To reduce the carbon footprint of building energy consumption, photovoltaic (PV) cell panels are increasingly being used to provide a solar, self-sustaining source of electricity in both homes and large buildings. However, the semiconductor material that converts the solar light energy to electricity does not function efficiently at elevated temperatures, and the performance of a hot PV cell degrades. Externally mounted panels often rely for their cooling on atmospheric air. One such PV panel that has a square face (1 m * 1 m), as shown in the figure, is mounted on the side face of a building with air flowing over across it in parallel. If the maximum allowable temperature of the PV panel always has to be <= 70°C, calculate the rate of convection heat loss from the face of the panel when
air at 25°C flows over it with a velocity of 1.0 m/s. What is the heat loss if the wind speed decreased to 0.25 m/s? Also, do the results change significantly if the airstream is not parallel to the panel but has a pitch and yaw angle, relative to the panel alignment, or strikes it perpendicularly? Note that the heat loss in many ways, gives the PV panel designers an estimate of the typical range of electricity generation and the PV cell operating efficiency. GIVEN • Air flows over PV panel surface of 1m*1m in parallel • Air temperature (Ta) = 25°C • Air velocity (Us) = 1 m/s • Maximum allowable temperature of PV panel (Tw) = 70°C FIND • Rate of Convection heat loss when the velocity is 1 m/s. • Rate of heat loss when air velocity is reduced to 0.25 m/s • Change in results if airstream is not parallel but strikes at an angle perpendicularly? ASSUMPTIONS • Steady state PROPERTIES AND CONSTANTS Thermal conductivity (k) = 0.0272 W/(m K) Kinematic viscosity (?) = 18.5 × 10–6 m2/s Prandtl number (Pr) = 0.71 At Tw: Prs = 0.71
The depth to which an inverted drinking glass must be pushed beneath the water surface to squeeze the enclosed air to half its volume is
A) 76 cm. B) 10.3 m. C) 14.7 m. D) 20.6 m. E) 29.4 m.
When atoms of an element are heated enough that they lose electrons, their emission and absorption spectra change
Indicate whether the statement is true or false