If one star has a temperature of 4000 K and another star has a temperature of 40,000 K, how much more energy per second will the hotter star radiate from each square meter of its surface? ____________________
Fill in the blank(s) with correct word
10,000 times
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The nucleus of a hydrogen atom, a proton, sets up an electric field. The distance between the proton and electron is about 5.1 × 10^?11 m. What is the magnitude of the electric field at this distance from the proton? [The charge on the proton is +1.6 × 10^?19 C.]
Hot water is used to heat air in a double pipe heat exchanger as shown in the following sketch. If the heat transfer coefficients on the water side and on the air side are 550 W/(m2K) and 55 W/(m2 K), respectively, calculate the overall heat transfer coefficient based on the outer diameter. The heat exchanger pipe is 5 cm, schedule 40 steel (k = 54 W/m K), with water inside.
GIVEN
• A double pipe heat exchanger with water in inner tube and air in the annulus
• Heat transfer coefficients
? Water side ih = 550 W/(m2 K)
? Air side oh = 55 W/(m2 K)
• Inner pipe: 5 cm, schedule 40 steel
• Pipe thermal conductivity (k) = 54 W/(m K)
FIND
• The overall heat transfer coefficient based on the outer diameter (Uo). ASSUMPTIONS
• Uniform heat transfer coefficients
SKETCH
PROPERTIES AND CONSTANTS
for 5 cm, schedule 40 pipe
? Outside diameter (Do) = 2.375 in = 6.033 cm=0.0603 m
? Wall thickness (t) = 0.154 in=0.39 cm=0.0039 m
Fig. 28-6 shows two long, parallel current-carrying wires. The wires carry equal currents I1 = I2 = 20 A in the directions indicated and are located a distance d = 0.5 m apart. Calculate the magnitude and direction of the magnetic field at a point located at an equal distance d from each wire.
a. 4?T upward b. 8?T upward c. 4?T to the right d. 8?T downward e. 4?T downward
About how many stars are visible on a clear, dark night with the naked eye alone?
A) a few dozen B) a few hundred C) a few thousand D) tens of thousands E) millions and millions