It would be easier to pull the evacuated Magdeburg hemispheres apart if they were
A) held upside down.
B) at sea level.
C) 20 km beneath the ocean surface.
D) 20 km above the ocean surface.
E) none of the above
Answer: D
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A metal plate is placed in the sunlight. The incident radiant energy G is 780 W/m2. The air and the surroundings are at 10°C. The heat transfer coefficient by natural convection from the upper surface of the plate is 17 W/(m2 K). The plate has an average emissivity of 0.9 at solar wavelengths and 0.1 at long wavelengths. Neglecting conduction losses on the lower surface, determine the equilibrium temperature of the plate.
GIVEN
- A metal plate is sunlight
- Incident radiant energy
- Temperature of air and surroundings
- Natural convection heat transfer coefficient
- Plate emissivity (?) = 0.9 at solar wavelengths, 0.1 at long wavelengths
FIND
-The equilibrium temperature of the plate (Tp)
ASSUMPTIONS
- Steady state
- Conduction losses on the lower surface of the plate are negligible
- The surroundings behave as a blackbody enclosure
SKETCH
PROPERTIES AND CONSTANTS
the Stephan-Boltzmann constant
Distant galaxies tend to be much bluer than those nearby
Indicate whether the statement is true or false
In beta decay the mass number (the total number of protons and neutrons) of the parent nuclide decreases by
A. 0 B. 2 C. 4 D. 6
A heater is rated at 1200 watts for a 120-volt source.If two heaters are connected in parallel across the 120-volt source, the total power in watts drawn from the source is
a. 600 b. 1200. c. 2400 d. none of the above.