Analyze the NASA sunspot image shown. Based on that image, what is (or was) the best year to go travel to high latitudes to see the Northern Lights?
a. 2001
b. 2009
c. 2012
d. 2014
2001
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Two mirrors are at right angles to one another. A light ray is incident on the first at an angle of 30° with respect to the normal to the surface. What is the angle of reflection from the second surface?
a. 30° b. 60° c. 45° d. 53° e. 75°
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
Two large, flat, horizontally oriented plates are parallel to each other, a distance d apart
Half way between the two plates the electric field has magnitude E. If the separation of the plates is reduced to d/2 what is the magnitude of the electric field half way between the plates? A) 4E B) 2E C) E D) 0 E) E/2
A machinist needs to punch a 5.0-cm-radius hole in a steel plate which is 0.45 cm thick. If the ultimate shear strength of steel is 2.50 × 10^8 Pa, what is the force required to accomplish this task?
a. 8.8E+5 N b. 3.5E+5 N c. 5.6E+6 N d. 1.1E+8 N