Time constant for the current through the inductor

  • Thread starter syhpui2
  • Start date
  • #1
28
0

Homework Statement



wjD8Y.png


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.
 
Last edited:

Answers and Replies

  • #2
gneill
Mentor
20,913
2,862
Kill the source (short the voltage supply) and remove the inductor. Find the equivalent resistance at the terminals where the inductor was.

attachment.php?attachmentid=40334&stc=1&d=1319604076.gif
 

Attachments

  • #3
28
0
Kill the source (short the voltage supply) and remove the inductor. Find the equivalent resistance at the terminals where the inductor was.

attachment.php?attachmentid=40334&stc=1&d=1319604076.gif

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

instead of 2L/R?

Thanks
 
  • #4
gneill
Mentor
20,913
2,862
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.
 

Related Threads on Time constant for the current through the inductor

Replies
2
Views
2K
  • Last Post
Replies
2
Views
1K
Replies
2
Views
6K
  • Last Post
Replies
19
Views
1K
  • Last Post
Replies
2
Views
4K
Replies
1
Views
588
Replies
34
Views
3K
Replies
1
Views
6K
  • Last Post
Replies
17
Views
768
Replies
4
Views
1K
Top