# Homework Help: B field inside solenoid as a result of iron rod

1. May 12, 2013

### CAF123

1. The problem statement, all variables and given/known data
Consider a solenoid with a time varying current and with a coil of wire placed around it. Suppose there is a soft iron rod inside the solenoid. My question is: What happens to the (induced) current in the coil of wire as a result?

2. Relevant equations

3. The attempt at a solution

Since iron is ferromagnetic, (it has associated with it a permanent magnetic dipole moment), it gives out a net B field. So the B field inside the solenoid is increased. Since $$\phi_B = BA,$$ the magnetic flux then increases and hence the induced emf in the wire by Faraday. This causes the induced current to increase also.

Is this okay?

Many thanks.

2. May 12, 2013

Looks good.