Need help on solving a RL circuit with switch

  • Engineering
  • Thread starter madcowdisease
  • Start date
  • #1

Homework Statement


tLfeD.jpg



Homework Equations


Find v(t) for t < 0 and t > 0 in the circuit.


The Attempt at a Solution


I tried to find the i through the inductor for both t=0- and t=infinity, but I did not get the same result as the answer given in the txtbook which is 96e-4t V. According to the answer given from the txtbk, if I'm not wrong, i(t) shud be i(t)=48e-4t A, and then to find v at the 2 ohm resistor, i(t) X 2 and u get v(t).

I do not really understand why, I've been on this qn for 1 hr and stil can't understand it.
Please help and thank you.
 

Answers and Replies

  • #2
berkeman
Mentor
59,332
9,462

Homework Statement


tLfeD.jpg



Homework Equations


Find v(t) for t < 0 and t > 0 in the circuit.


The Attempt at a Solution


I tried to find the i through the inductor for both t=0- and t=infinity, but I did not get the same result as the answer given in the txtbook which is 96e-4t V. According to the answer given from the txtbk, if I'm not wrong, i(t) shud be i(t)=48e-4t A, and then to find v at the 2 ohm resistor, i(t) X 2 and u get v(t).

I do not really understand why, I've been on this qn for 1 hr and stil can't understand it.
Please help and thank you.

What's I_o?
 
  • #3
Io is I0, the value should be calculated when t=o-
 
  • #4
berkeman
Mentor
59,332
9,462
Io is I0, the value should be calculated when t=o-

It's a bit confusing for me, but to clarify... So the switch is opened at t=0? And right before then, there is 1*I_o flowing to the left, and 3*I_o flowing to the right? To add up to the 4*I_o that is supplied by the dependent current source in the middle?
 
  • #5
vela
Staff Emeritus
Science Advisor
Homework Helper
Education Advisor
14,986
1,563
I think the idea is that at t=0, the 3-ohm branch is disconnected and the 8-ohm branch is connected. The controlled source is a voltage source since it has the + and - signs in it, not an arrow.

I noticed there's a little o symbol right below the arrow for current i. Is that significant?
 

Related Threads on Need help on solving a RL circuit with switch

  • Last Post
Replies
9
Views
721
Replies
3
Views
3K
Replies
3
Views
1K
  • Last Post
Replies
1
Views
836
Replies
1
Views
5K
Replies
3
Views
14K
Replies
4
Views
2K
  • Last Post
Replies
6
Views
4K
Replies
5
Views
1K
Top