# B Induced current by moving bar magnet external to solenoid.

1. May 31, 2017

### Coolamebe

Hi, I was wondering whether a bar magnet would induce a current if it was moving external to the solenoid, rather than within the coil. I see no reason why it wouldn't occur, but I've never seen it displayed or mentioned so I'm not sure. Thank you.

2. May 31, 2017

The external magnetic field from a long bar magnet loops around from the + pole end to the - pole end, and falls off in strength as one moves away from the ends. Thereby if you move a long bar magnet towards a solenoid, there will be an EMF $\varepsilon=-\frac{d \Phi}{dt}$. With known magnetic field strength and pattern, it would be possible to accurately compute the EMF that occurs for the motion of the magnet towards the solenoid at a given speed. An experiment like this could make for a good science project and/or undergraduate laboratory exercise.