HW9solutions_short

HW9solutions_short - Physics 213 Homework 9 Solutions...

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Physics 213 Homework 9 Solutions Spring 2008 29.17. IDENTIFY and SET UP: Apply Lenz's law, in the form that states that the magnetic flux due to the induced current tends to oppose the change in flux. EXECUTE: (a) With the switch closed the magnetic field of coil A is to the right at the location of coil B. When the switch is opened the magnetic field of coil A goes away. Hence, by Lenz's law the magnetic field due to the current induced in coil B is to the right, to oppose the decrease in the flux in this direction. To produce magnetic field directed to the right, the current in the circuit with coil B must flow through the resistor in the direction a to b . (b) With the switch closed the magnetic field due coil A is to the right at the location of coil B. This field is stronger at points closer to coil A, so when coil B is brought closer, the magnetic flux through coil B increases. By Lenz's law the magnetic field due to the induced current in coil B is to the left to oppose the increase in flux to the right. To produce magnetic field that is to the left, the current in the circuit with coil B must flow through the resistor in the direction b to a . (c) With the switch closed the magnetic field due to coil A is to the right at the location of coil B. The current in the circuit that includes coil A increases when R is decreased and the magnetic field due to coil A increases when the current through the coil increases. By Lenz's law the magnetic field due to the induced current in coil B is to the left to oppose the increase in magnetic flux to the right. To produce magnetic field that is to the left, the current in the circuit with coil B must flow through the resistor in the direction b to a . EVALUATE: In parts (b) and (c) the change in the circuit causes the flux through circuit B to increase, and in part (a) it causes the flux to decrease. So the direction of the induced current is the same in parts (b) and (c) and opposite in part (a).

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This note was uploaded on 08/27/2008 for the course PHYS 2213 taught by Professor Perelstein,m during the Spring '07 term at Cornell.

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HW9solutions_short - Physics 213 Homework 9 Solutions...

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