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SaraF
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Homework Statement
This is a question from the Princeton Review of AP physics B, 2011 edition. A small circular loop of wire (radius r) is placed on an insulating stand inside a hollow solenoid of radius R. The solenoid has n turns per unit length and carries a counterclockwise current I. (The magnetic field within the solenoid is shown as pointing into the plane of the page.) If the current in the solenoid is decreased at a steady rate of a amps per second, determine the induced emf and the direction of the induced current in the loop.
Homework Equations
B = uonI. E = -d(BA)/dt
The Attempt at a Solution
I determined the equation for the EMF induced in the small loop correctly. I had a problem with the direction of the current. By the right hand rule, the current should be clockwise, and that is the text's correct answer. However, by the same right hand rule, I would expect the counterclockwise current in the solenoid to produce a magnetic field pointing out of the plane of the page, not into it.
Initially, I thought that the current in the small loop would be counterclockwise, because that is the direction specified for the current in the solenoid. Since the solenoid current is decreasing, the current induced in the ring would oppose that decrease, and therefore be in the same direction as the current in the solenoid, ccw. Now I am confused as to how a ccw current in the solenoid could even produce a magnetic field pointing into the plane of the page, as that conflicts with the right hand rule. I'm hoping that someone can clear up this confusion for me.