A long, straight, current-carrying wire passes near a wire loop. The current in
ID: 1707134 • Letter: A
Question
A long, straight, current-carrying wire passes near a wire loop. The current in the straight wire is directed to the right, and its magnitude is decreasing. (a) What is the direction of the magnetic flux through the loop? (b) Is the magnitude of the flux through the loop increasing or decreasing with the time? (c) What is the direction of the magnetic field produced by the induced current in the loop? (d) What is the direction of the current induced in the loop? (e) This induced current leads to a magnetic force on the loop. What is the direction of this force? Is it directed toward the wire or away from it?
Figure P21.19
Explanation / Answer
Use the right hand rule for the wire on a. So to the right means above the wire is out of the page and below the wire is into the page.
(a) INTO THE PAGE
current creates the magnetic field and it is decreasing. Magnetic flux is the amount of magnetic field passing through an area. So since current is proportional to magnetic field, the magnitude of the flux is...
(b) DECREASING
Current must create a field to resist the change. So it must make a current to oppose the loss of the magnetic field. By the magic of the right hand rule we know that the direction of the magnetic field produced by the induced current in the loop is
(c) INTO THE PAGE
d is the same logic and is
(d) CLOCKWISE
current is clockwise so use the right hand rule to find the direction of the force which is
(e) TOWARD THE WIRE
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