# Magnetic n electric energy

1. Feb 6, 2005

### juhi

hi
i am not exactly able to understand in which form or rather how electric and magnetic energy get stored in capacitor and inductor respectively... :shy:

2. Feb 6, 2005

### Crosson

In a capacitor, one of the plates has excess positive charge and the other plate has excess negative charges. The negative charges want to fall towards the positive plate, just like we fall towards the earth.

As long as those charges are some distance apart (as long as an object is off the ground) there is stored up potential energy. It is our choice to say that the energy is "stored in the charges" or that the energy is "stored in the particle's field at all points in space", the mathematics can accomadate either interpretation.

I will let some one else explain an inductor for you.

3. Feb 7, 2005

### juhi

thanks a lot..

4. Feb 12, 2005

### heman

that was a very nice explanation CROSSON.....but when it is said that the space betn. plates is ""filled"" with electrical energy...how to explain this....

5. Feb 12, 2005

### kanato

Since we are talking about stored potential energy when there is a charge separation, we can attribute that to the electric field, since whenever there is a charge separation there will be an electric field. Calculation of the total energy is given by
$$\int_{\hbox{All Space}} \frac{1}{2}\epsilon_0 \vec{E}^2 dV$$

so it makes sense to identify the integrand as the energy density as a function of position. And notice that the energy density is zero or very small at points where the electric field is zero or very small. In a capacitor we usually treat the electric field as being entirely inside the capacitor and neglect fringe fields, we consider that as being where all the energy is.