Electricity Question

[4563728]

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If we have a closed loop with a straight wire in the middle of the loop (not attached to the loop) and a current is running through both, does the straight wire in the loop generate a current?

According to Kaplan it doesn't and I would clarification as to why this is. Thanks!

 

[Cmdr_Shepard]

Can you post a diagram? The answer is possibly different depending on the orientation of the two wires, and whether there's a battery.

 

[4563728]

Here it is!

 

[Cmdr_Shepard]

The answer should be A. There are two steps to this. Because you are trying to find out what happens to the straight wire, you need to know which direction the current is flowing in the wire, and the orientation of the magnetic field that is bathing the wire. The first we know (depicted), and the second we get from the loop.

If you use the RHR (curl) for the loop, you will notice that the magnetic field goes INTO the page inside the loop, and OUT OF the page outside the loop. Then, use the RHR again (straight fingers) and orient your thumb in the direction of the current (up), and orient your straight fingers in the direction of the magnetic field (into the page). This forces your palm to point to the left, which specifies the direction of the electric force and thus acceleration of the wire.

 

[4563728]

For the second RHR, are you pointing your thumb in the direction of the current of the straight wire? Also, doesn't the straight wire create a magnetic field as well? Don't we have to take that into consideration?

 

[Cmdr_Shepard]

Yes, pointing my thumb up, in the same direction as the current in the straight wire. And you should think of the sequence of events as:

-switch is closed creating a current in the loop
-magnetic field created in loop
-magnetic field in loop induces current in straight wire
-induced current in straight wire generates magnetic field with orientation opposite to the magnetic field that induced the current (out of page)

The magnetic field generated by the straight wire is much smaller and counter to the loop magnetic field (inside the loop), so the net field is still into the page inside the loop.