Time constant for the current through the inductor

[syhpui2]

Homework Statement

http://i.imgur.com/wjD8Y.png

In the circuit below, V = 6 volts, R = 10 ohms, L = 100 mH. The switch has been open for a long time. Then, at time t = 0, the switch is closed.



What is the time constant for the current through the inductor?

2L / R

Homework Equations

TAU=l/R

The Attempt at a Solution

I am not sure how do I find the equvialent resistance in this case.

 

[gneill]

Kill the source (short the voltage supply) and remove the inductor. Find the equivalent resistance at the terminals where the inductor was.

 

[syhpui2]

Kill the source (short the voltage supply) and remove the inductor. Find the equivalent resistance at the terminals where the inductor was.

Equvialent resistance is 2r then time constant should be L/2R?

instead of 2L/R?

Thanks

 

[gneill]

Equvialent resistance is 2r then time constant should be L/2R?

instead of 2L/R?

Thanks

Nope. Those two resistors are not in series with respect to the open terminals. So the resistance is R/2. That makes your time constant 2L/R.