We can find the masses and diameters of stars that are in eclipsing binary systems

Indicate whether the statement is true or false


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Physics & Space Science

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Carbon dioxide is the predominant atmospheric gas on Venus

Indicate whether the statement is true or false

Physics & Space Science

What does the polarization of starlight tell us about the dust grains and the Galaxy?

What will be an ideal response?

Physics & Space Science

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

Physics & Space Science

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°

Physics & Space Science