Which dwarf planet does NOT have a moon?
A. Ceres
B. Haumea
C. Pluto
D. Makemake
E. Eris
Answer: A
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The cosmological redshift is actually not a velocity at all, but a measure of the expansion of space-time
Indicate whether the statement is true or false
Liquid oxygen at -183°C is stored in a thin walled spherical container with an outside diameter of 2 m. This container is surrounded by another sphere of 2.5 m inside diameter to reduce heat loss. The inner spherical surface has an emissivity of 0.05 and the outer sphere is black. Under normal operation the space between the spheres is evacuated but an accident resulted in a leak in the outer sphere and the space is filled with air at 100 kPa. If the outer sphere is at 25°C, compare the heat losses before and after the accident.
GIVEN
? A sphere filled with liquid oxygen surrounded by a larger sphere
? Sphere diameters ? Di = 2 m
? Do = 2.5 m
? Emissivity of inner sphere (?) = 0.05
? Outer sphere temperature (To) = 25°C = 298 K
? Liquid oxygen temperature (Ti) = –183° = 90 K
? Outer sphere is black
FIND
The rate of heat loss with
(a) A vacuum between the spheres
(b) Air at 100 kPa between the spheres
ASSUMPTIONS
? Steady state
? The internal convective resistance and the resistance of the inner sphere wall are negligible
SKETCH
PROPERTIES AND CONSTANTS
The thermal expansion coefficient (B) ? 1/T = 1/(194 K) = 0.0052 1/K
Extrapolating from Appendix 2, Table 27, for dry air at the mean temperature of –79°C from values at 0°C and 20°C
What is the wavelength of the emitted photon if an electron in the hydrogen atom makes a transition from the ni = 2 to the nf = 1 state?
A) 205.2 nm B) 87.5 nm C) 91.2 nm D) 121.5 nm E) 402.1 nm
If an all electric house uses 2400 kWh in a month, what will the amount of the bill for electricity be at a rate of 9.5 cents per kWh?
A) $23 B) $2280 C) $228 D) $25,300 E) $11.50