Two identical coils of wire are placed on a single horizontal wooden broom handle. The coils are separated by a few centimeters. We now run identical currents in the same direction through each coil. The coils experience
A. a repulsive magnetic force.
B. a repulsive electrostatic force because both coils are identically charged.
C. an attractive electrostatic force because one coil is negatively charged and the other positively charged.
D. no forces because the currents are identical.
E. an attractive magnetic force.
Answer: E
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Consider a heat treatment process in which steel rods with a 10 cm diameter at an initial temperature of 600°C are inserted into an oil bath at 25°C. Assuming a convection coefficient of 400 W/(m2 K) between the oil and the rod, estimate how long it takes for the centerline of the rod to cool to 60°C. If the steel rod, which is 1 m long, is withdrawn from the bath at this point in the process, i.e., when the centerline temperature has reached 60°C, estimate the rate at which heat must be extracted from the oil to maintain its temperature constant during the process of treating 25 rods per hour.
GIVEN
• Heat treatment of steel rod inserted in oil bath
• Rod outside diameter = 0.1 m
• Initial temperature (T0) = 600°C
• Oil bath temperature (T?) = 25°C
• The average heat transfer coefficient ch = 400 W/(m2 K)
FIND
• Time it takes for centerline of the rod to cool to 600C.
• Rate at which heat must be extracted from oil to maintain its temperature constant during the process of treating 25 rods per hour.
ASSUMPTIONS
• Radial conduction only in billet
• Uniform and constant properties
SKETCH
Pure water is classified as
A. an insulator. B. a conductor. C. a semiconductor. D. all of these choices are correct E. none of these choices are correct
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A) moving to the right at speed c B) gradually catching up to him at speed 0.1c C) moving to the right at speed 1.9c D) moving to the left at 0.1c
How do astronomers think Jupiter generates its internal heat?
A) chemical processes B) radioactive decay C) nuclear fusion in the core D) by contracting, changing gravitational potential energy into thermal energy E) internal friction due to its high rotation rate