# Homework Help: Source free RL circuits

1. Sep 10, 2007

### juicev85

We just started source free RL circuit analysis in my circuits class (very easy).
However there is a problem in the HW I am not quite sure how to solve.

Problem: The circuit shown consists of a resistance R = 1 ohm and an inductance l = 2H. At t=0, the inductance is storing 100mJ of energy. Calculate (a) i at t=1s (b) the energy remaining in the inductance at t = 2s.

I can easily solve the problems that give an initial current at t = 0s, but i am not sure about the joules. I know joules are watts/second is there some kind of conversion I can perform to get the current so I can use the I L(t) = 2e^-Rt/L formula. This is an easy problem it just comes down to the fact that the prof. didn't mention anything like this in the lecture. So if you guys can give me the tools I am sure I can solve it.

2. Sep 11, 2007

### AlephZero

There is a formula for the energy stored in an inductor - it depends on L and I. Check that out in your notes or textbook and use it to find the initial current.

3. Sep 11, 2007

### Astronuc

Staff Emeritus
It would help if the circuit was shown.

BTW - joules are watt-seconds, or watts (W, power) = Joules (energy)/second