How is Earth's magnetic field generated?
What will be an ideal response?
Convection currents stir the liquid metal in Earth's core, and it also rotates as Earth rotates. Because of these motions, and because it is a very good conductor of electricity, the liquid outer core generates a magnetic field through the dynamo effect.
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A CD has a diameter of 12.0 cm. If the CD is rotating at a constant angular velocity of 20.0 radians per seconds, then the period of the rotational motion is
A. 0.314 s. B. 0.441 s. C. 0.582 s. D. 0.698 s. E. 0.750 s.
You are driving along a highway at 25.0 m/s when you hear the siren of an emergency vehicle traveling in the opposite direction on the other side of the highway
When the vehicle is approaching you, you hear the frequency of the siren as 2380 Hz, but when it is past you the frequency becomes 1680 Hz. What is the frequency of the siren? The speed of sound in air is 343 m/s. A) 1850 Hz B) 2000 Hz C) 2050 Hz D) 2010 Hz E) 1980 Hz
Determine the heat transfer area requirements of Problem 10.40 if (a) 1-2 shell and tube, (b) an unmixed crossflow, and (c) a parallel flow heat exchanger are used, respectively.
GIVEN
• An air-to-gas heat exchanger
• Entering temperatures
? Ta,in = 350°C
? Tg,in = 700°C
• Mass flow rates: ma = mg = 5 kg/s
• Specific heats: cpa = cpg = 1.05 kJ/(kg K) = 1050 J/(kg K)
• Overall heat transfer coefficient (U) = 75 W/(m2 K)
FIND
The heat transfer area (A) as a function of the effectiveness (e) for (a) A 1-2 shell and tube heat exchanger (b) An unmixed crossflow heat exchanger (c) A parallel flow heat exchanger
ASSUMPTIONS
• For case (a) the air is in the tubes
SKETCH
Consider the loop of flexible wire shown below. If we pass a current through the loop, will it tend to expand (becoming more circular), scrunch up even more tightly, or do nothing?
A. Expand
B. Scrunch up
C. Do nothing
D. The answer depends on the current’s direction.