# Magnetic flux and induction help

1. Apr 17, 2009

### latentcorpse

$epsilon=-\frac{d \Phi}{dt}$ where epsilon is the emf. the emf produces a current in the oppostite direction to the loop which gives a magnetic field opposing ther external field B. my notes then say

$\frac{d \Phi}{dt}>0 \Rightarrow \frac{d \Phi_{Induced}}{dt}<0$ but i don't understand this statement, can someone explain it please?

2. Apr 17, 2009

### rl.bhat

Re: Induction

Changing magnetic flux produces the changing current in the loop. This changing current produces changing magnetic flux which links the loop resulting changing induces magnetic flux in the opposite direction. One is taken as positive and the other is taken as negative.

3. Apr 17, 2009

### latentcorpse

Re: Induction

sorry what?

is it basically lenz's law yeah?

the changing magnetic flux causes an electric field round the wire which induces a current round the loop, this current is changing with time and in turn produces a changing magnetic field in the oppostie direction to the original external field and so the induced flux has the opposite sign to the flux of the external field?