We can find the masses and diameters of stars that are in eclipsing binary systems
Indicate whether the statement is true or false
T
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What does the polarization of starlight tell us about the dust grains and the Galaxy?
What will be an ideal response?
A homeowner wants to replace an electric hot-water heater. There are two models in the store. The inexpensive model costs $280 and has no insulation between the inner and outer walls. Due to natural convection, the space between the inner and outer walls has an effective conductivity of 3 times that of air. The more expensive model costs $310 and has fiberglass insulation in the gap between the walls. Both models are 3.0 m tall and have a cylindrical shape with an inner wall diameter of 0.60 m and a 5 cm gap. The surrounding air is at 25°C, and the convective heat transfer coefficient on the outside is 15 W/(m2 K). The hot water inside the tank results in an inside wall temperature of 60°C. If energy costs 6 cents per kilowatt-hour, estimate how long it will take to pay back the extra
investment in the more expensive hot-water heater. State your assumptions.
GIVEN
FIND
- The time it will take to pay back the extra investment in the more expensive hot-water heater
ASSUMPTIONS
- Since the diameter is large compared to the wall thickness, one-dimensional heat transfer is
assumed
- To simplify the analysis, we will assume there is no water drawn from the heater, therefore the
inside wall is always at 60°C
- Steady state conditions prevail
SKETCH
PROPERTIES AND CONSTANTS
fiberglass (ki) = 0.035 W/(m K) at 20°C
dry air (ka) = 0.0279 W/(m K) at 60°C
Carbon dioxide is the predominant atmospheric gas on Venus
Indicate whether the statement is true or false
Unpolarized light of intensity I0 passes through two sheets of ideal polarizing material. If the transmitted intensity is 0.375I0, what is the angle between the polarizers?
a. 22.5° c. 30° b. 60° d. 45°