# Mutual Induction and Law of Conservation of Mass

1. Jun 24, 2015

### Nishantkumar19

In mutual induction, when a coil is turned on or off, it generates voltage in another nearby coil. But where is that voltage coming from? It can't be created, so what form of energy does it convert from?

As far as I know, when the magnetic field cuts across the coil, that generates voltage, but does the magnetic field itself lose energy that is being converted to voltage in the second coil?

2. Jun 25, 2015

### Drakkith

Staff Emeritus
Yes, the energy comes from the magnetic field, which comes from the first coil.

3. Jun 25, 2015

### tech99

If the second coil is open circuit, no energy flows to it. When the first coil has a varying magnetic field, as with AC, it applies an electro motive force to the electrons in the secondary, but as there is an open circuit they cannot move and so no energy is absorbed.

4. Jun 25, 2015

### Drakkith

Staff Emeritus
What does this have to do with the OP's question or my response?

5. Jun 25, 2015

### tech99

My apologies if I have missed the point, but the questioner seemed to be asking if, to induce a voltage in a nearby coil, energy is taken from the field of the primary, and that was the direction of my reply.

6. Jun 25, 2015

### Drakkith

Staff Emeritus
I see. It seemed like you were chiming in just to point out something about an open circuit. No worries.

7. Jun 28, 2015

### Nishantkumar19

Does that mean the primary field loses energy over time?

Does the same apply for when an electromagnetic field attracts iron objects?

Is it the size of the field that diminishes, or the attracting energy itself?