# Finding time constant of current decay in closed circuit

1. Sep 3, 2008

### GarethB84

Hi this is my first post so please be nice :)

1. The problem statement, all variables and given/known data
The problem has been set up that a circuit containing a resistor and switch is being driven by a power source of unkown potential. The switch is flick to short the power source leaving only the resistor in a closed loop.
Calculate the current decay.
Initial current = 100A
Resistance = 1n$$\Omega$$

2. Relevant equations

V=IR
Power = I2R

3. The attempt at a solution

I'm not too sure. The power generated, and hence the heat loss can be found to be 1e-5W so thats 1e-5 Joules per second of heat loss.

I'm not sure if we have enough information. Current decay involving inductance or capacitance is well known but just a resistor in a circuit of 'ideal' conductors?

I'm assuming it is an exponential decay of form I=I0e-t/$$\tau$$ but finding the decay constant is proving tricky. Any advice????