# I What is induced magnetic field?

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1. Oct 17, 2016

### Aafia

What is emf in the coil? As far as I know about emf is that it is potential difference between two terminals of a source but what if it is induced in coil by changing flux linkage. What exactly happen when emf is induced?

2. Oct 17, 2016

### arpon

When there is EMF in a circuit, electric field is produced across the circuit. Due to this electric field, the free charges (electrons) move and electric current flows.
You can define emf between points $A$ and $B$ as
$$\int^A_B \vec E \cdot \vec{dl}$$
Here line integral of electric field $E$ is evaluated around the circuit from point $A$ to $B$.
For induced emf, we will consider closed loop integral, i.e, $$\oint_C\vec E \cdot \vec{dl}$$
where $\vec E$ is electric field, $\vec{dl}$ is an infinitesimal line element on the loop (i.e, the coil) $C$.

3. Oct 17, 2016

### Aafia

This is making sense to me. But does this electric field is produced across battery terminals because what my teacher told me is

"emf is the potential difference between positive and negative terminal of the battery"

4. Oct 17, 2016

### arpon

I meant that electric field is produced in the circuit. Just look at this figure:

I have shown the direction of electric field. Please do not hesitate to ask if you have any further question.

5. Oct 17, 2016

### davenn

More correctly, the Voltage is the potential difference across the terminals of the battery or other PSU
You cannot have a "force" unless something is moving ie. till the battery is connected to a circuit and the current starts to flow

to quote @sophiecentaur from another recent thread

Dave