AP Unit III D. 2. Forces on current carrying wires in magnetic fields. Students should understand the force exerted on a current carrying wire in a magnetic field, so they can:
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AP Unit III D
2. Forces on current carrying wires in magnetic fields
x means magnetic field B going INTO paper
. means field coming out of paper
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Conventional Current
Direction of force given by Fleming’s Left hand Motor Rule – thuMb – Motion, First finger – field (pointing towards south), seCond finger – current
 ve
+ ve

Which way will the loop turn?
This is the motor effect.
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Top view
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Side view
The force (F) on the wire is equal to the magnetic field strength B x current I x length of wire L. (F= BIL) A charge moving in a magnetic field will also undergo a force. The force F is equal to the magnetic field strength B x charge Q x velocity of charge v (F= BQv)