Answer: mu 0 n 1 n 2 Al.
- A mu<sub>0</sub> n<sub>1</sub> n<sub>2</sub> Al
- B mu<sub>0</sub> n<sub>1</sub> n<sub>2</sub> A
- C mu<sub>0</sub> n<sub>1</sub> A/n<sub>2</sub>
- D mu<sub>0</sub> n<sub>1</sub><sup>2</sup> Al
Correct answer: A. mu<sub>0</sub> n<sub>1</sub> n<sub>2</sub> Al
Explanation: M = mu<sub>0</sub> n<sub>1</sub> n<sub>2</sub> A l (for closely wound coaxial solenoids). Flux linkage from inner to outer = n<sub>2</sub> l x mu<sub>0</sub> n<sub>1</sub> I x A.
As a magnet approaches a coil, flux rises steadily and a constant non-zero EMF is induced (Faraday's law). Once the magnet stops moving, flux stays constant and the induced EMF drops to zero - EMF only exists while flux is actively changing.
Concept context
Faraday's and Lenz's laws, motional EMF, self/mutual inductance, eddy currents, and the AC generator - how a changing magnetic flux creates an electric current.