At what speed, relative to the frame of the observer making the measurement, is the length of a meter stick 0.60 m?
A)
0.80c
B)
0.60c
C)
0.50c
D)
0.70c
E)
0.90c
A
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What physical property of a star does the spectral type measure?
A) density B) luminosity C) temperature D) mass E) composition
To measure thermal conductivity, two similar 1-cm-thick specimens are placed in an apparatus shown in the accompanying sketch. Electric current is supplied to the 6-cm by 6-cm guarded heater, and a wattmeter shows that the power dissipation is 10 watts (W). Thermocouples attached to the warmer and to the cooler surfaces show temperatures of 322 and 300 K, respectively. Calculate the thermal conductivity of the material at the mean temperature in W/(m K).
GIVEN
Thermal conductivity measurement apparatus with two samples as shown
Sample thickness (L) = 1 cm = 0.01 cm
Area = 6 cm ? 6 cm = 36 cm2 = 0.0036 m2
Power dissipation rate of the heater (qh) = 10 W
Surface temperatures
Thot = 322 K
Tcold = 300 K
FIND
The thermal conductivity of the sample at the mean temperature in W/(m K)
ASSUMPTIONS
One dimensional, steady state conduction
No heat loss from the edges of the apparatus
SKETCH
Which of the following is not considered a likely solution to the question of why we are not currently aware of a galactic civilization?
A) There is no galactic civilization because civilizations are not common. B) There is no galactic civilization because civilizations do not leave their home worlds. C) The galactic civilization is deliberately avoiding contact with us. D) The galactic civilization probably is undetectable to us because it makes use of technologies that do not obey the known laws of physics. E) There is no galactic civilization because most civilizations destroy themselves before achieving interstellar travel.
The Cenozoic era represents a period of
A) almost continuous tectonic activity. B) relative tectonic stability. C) worldwide tropical climates. D) great diversification of fish species.