Find the average density of a red giant star with a mass of 20 × 10^30 kg (approximately 10 solar masses) and a radius of 150 × 10^9 m (equal to the Earth's distance from the Sun)
a. 1.41 × 10^?4 kg/m3
b. 0.007 kg/m3
c. 1.41 kg/m3
d. 710 kg/m3
e. 1.41 × 10^?3 kg/m3
e
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Ordinary matter in the form stars and planet makes up approximately what proportion of the total mass and energy in the universe?
A) about 70 percent B) a few percent C) about 25 percent D) nearly a 100 percent
What is meant by a heat flow line?
What will be an ideal response?
A square silicone chip 7 mm by 7 mm in size and 0.5 mm thick is mounted on a plastic substrate as shown in the sketch below. The top surface of the chip is cooled by a synthetic liquid flowing over it. Electronic circuits on the bottom of the chip generate heat at a rate of 5 watts that must be transferred through the chip. Estimate the steady state temperature difference between the front and back surfaces of the chip. The thermal conductivity of silicone is 150 W/(m K).
GIVEN
A 0.007 m by 0.007 m silicone chip
Thickness of the chip (L) = 0.5 mm = 0.0005 m
Heat generated at the back of the chip (Gq) = 5 W
The thermal conductivity of silicon (k) = 150 W/(m K)
FIND
The steady state temperature difference (?T)
ASSUMPTIONS
One dimensional conduction (edge effects are negligible)
The thermal conductivity is constant
The heat lost through the plastic substrate is negligible
SKETCH
A wave travels at 175 m/s along the x-axis. If the period of the periodic vibrations of the wave is 3.00 milliseconds, then what is the wavelength of the wave?
A. 25.5 cm B. 35.6 cm C. 42.9 cm D. 49.5 cm E. 52.5 cm