Briefly describe the evidence suggesting that a 10-km asteroid or comet hit Earth at the time of the dinosaur extinction
What will be an ideal response?
A layer of clay at this level in the sediments is rich in materials found in asteroids but not normally found on Earth's surface. A crater off the Yucatan peninsula dates to the right time and is the right size.
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The heating surface is gray (emissivity = 0.8) while the receiver has a black surface. The lower plate is heated uniformly over its surface with a power input of 300 W. Assuming that heat losses from the backs of the radiating surface and the receiver are negligible and that the surroundings are at a temperature of 27°C, calculate the following
A 10 cm square, electrically heated plate is placed in a horizontal position 5 cm below a second plate of the same size as shown schematically.
(a) The temperature of the receiver
(b) The temperature of the heated plate.
(c) The net radiation heat transfer between the two surfaces.
(d) The net radiation loss to the surroundings.
(e) Estimate the effect of natural convection between the two surfaces on the rate of
heat transfer.
GIVEN
A square heated plate below a second plate of equal size as shown above
Plate size = 10 cm x 10 cm = 0.1 m x 0.1 m
Distance between plates (L) = 5cm = 0.05 m
Heated surface (A1) is gray with an emissivity (?1) = 0.8
Receiver (A2) is black (?2 = 1.0)
Heater power input
FIND
(a) The temperature of the receiver (T2)
(b) The temperature of the heated transfer (T1)
(c) The net radiation heat transfer (q12)
(d) The net radiation loss to the surroundings (qs)
(e) Estimate the effect of natural convection
ASSUMPTIONS
Steady state
Heat losses from the back of each plate are negligible
Temperature of surroundings (T3) = 27°C = 300 K
The surroundings behave as a blackbody enclosure
PROPERTIES AND CONSTANTS
the Stephan-Boltzmann constant
A clarinet behaves like a tube closed at one end. If its length is 1.0 m, and the velocity of sound is 344 m/s, what is its fundamental frequency (in Hz)?
A. 264 B. 140 C. 86 D. 440 E. 172
Resistances connected in parallel all have
A. the same current.
B. the same potential difference.
C. different voltages.
D. the same charge.
A double-slit interference experiment is performed in the air. Later, the same apparatus is immersed in benzene (which has an index of refraction of 1.50), and the experiment is repeated
When the apparatus is in benzene, you observe that the interference fringes are A) more widely spaced than when the apparatus is in air. B) equally spaced as when the apparatus is in air. C) more closely spaced than when the apparatus is in air.