Back emf and battery emf in RL Circuit

  • Thread starter k5591002
  • Start date
  • #1
k5591002
1
1
hello all!:smile:

I have a question about electromagnetism.
The question is "Can the back emf ever be greater than the battery emf in RL circuit?"

can someone explain this one for me plz?
 
  • Like
Likes Mujahid Rasool

Answers and Replies

  • #2
Chen
977
1
I'm assuming the resistor R and the inductor L are connected in series. As you know the effective V of the source in RLC circuits like this is given by:

[tex]V_S = \sqrt{(V_L - V_C)^2 + V_R^2}[/tex]
(all voltages are effective)

In this case however, we don't have a capacitor so it's actually just:

[tex]V_S = \sqrt{V_L^2 + V_R^2}[/tex]

With some basic operations you can find that:

[tex]V_L = \sqrt{V_S^2 - V_R^2}[/tex]

And therefore the answer is No, the back EMF on the inductor cannot be greater than the EMF of the battery. (This is because there is no capacitor in the circuit, if there was one then it would be possible for the back EMF of the inductor to outgrow the EMF of the battery.)
 
Last edited:
  • #3
mmwave
211
2
Originally posted by k5591002
hello all!:smile:

I have a question about electromagnetism.
The question is "Can the back emf ever be greater than the battery emf in RL circuit?"

can someone explain this one for me plz?

I'm not sure of your definition of back emf but one thing novice designers of inductive circuits learn the hard way is that when you interrupt the current in an inductor (say by opening a relay or turning off the base drive to a transistor) the inductor will generate whatever voltage is necesary to maintain that current until the energy stored in the mag. field is gone. That's why inductors in switching circuits have a diode across them, to give a path for the current when you turn the transistor off (or open a switch). Putting in a larger transistor just makes for larger fireworks.
 

Suggested for: Back emf and battery emf in RL Circuit

Replies
14
Views
339
  • Last Post
Replies
4
Views
640
Replies
9
Views
361
  • Last Post
Replies
6
Views
717
  • Last Post
Replies
10
Views
813
  • Last Post
Replies
9
Views
864
  • Last Post
Replies
3
Views
451
  • Last Post
3
Replies
103
Views
2K
Replies
5
Views
558
Top