What did the COBE satellite find regarding the smoothness of the cosmic background radiation?
What will be an ideal response?
COBE found that the cosmic background radiation has a perfect thermal radiation spectrum, with a peak corresponding to a temperature of 2.73 K. However, it also found slight fluctuations in the radiation. The temperature varies very slightly from one place to another by a few parts in 100,000.
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What did Tycho do that advanced astronomy significantly?
a. He realized that orbits didn’t have to be circles, they could be ellipses. b. He made more accurate observations than anyone before him. c. He thought of the idea of circles moving on circles (epicycles) to explain planetary motion.
A sphere 20 cm in diameter containing liquid air (–140°C) is covered with 5-cm-thick glass wool (50 kg/m3 density) with an emissivity of 0.8. Estimate the rate of heat transfer to the liquid air from the surrounding air at 20°C by convection and radiation. How would you reduce the heat transfer?
GIVEN
• A sphere containing liquid air covered with glass wool
• Sphere diameter (Ds) = 20 cm = 0.2 m
• Liquid air temperature (Ta) = – 140°C = 133 K
• Surrounding air temperature (T?) = 20°C = 293 K
• Insulation thickness (s) = 5 cm = 0.05 m
• Insulation emissivity (?) = 0.8
FIND
• Rate of heat transfer from liquid air to surrounding air
(q)
• How can this be reduced?
ASSUMPTIONS
• Steady state conditions
• The surroundings behave as a black body enclosure at T?
• Surrounding air is still
• Thermal resistance of the convection inside the sphere and of the container wall are negligible
SKETCH
PROPERTIES AND CONSTANTS
the Stephan-Boltzmann constant (?) = 5.67 × 10–8 W/(m2 K4).
the thermal conductivity of glass wool (ki) = 0.037 W/(m K)
Exclusion Principle: How many values of the magnetic quantum number, m?, correspond to a value of ? = 4?
A. 3 B. 5 C. 8 D. 9 E. 7
The major difference between transverse and longitudinal waves is the
a. direction of the wave motion. b. phase difference. c. direction of the particle displacement with respect to the direction of wave motion. d. size of the waves.