Does a current instantaneously disappear?

  • #1
perplexabot
Gold Member
329
5
Hi all. I was working on a circuit question with inductors and I then had a question. Lets say we have a simple circuit with only a resistor, an emf source and a switch. We first close the switch and the current goes though. Now after some time we open the switch.

My question is: Just after we open the switch does the current instantly go to zero? Or will the resistor have a current running through it at that instant and then decay?

Thank you
 

Answers and Replies

  • #2
Drakkith
Staff Emeritus
Science Advisor
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I believe the EMF takes a finite time to propagate, so when you open the switch not only is there a small amount of time that it takes for the switch to completely cut the voltage and current, the rest of the circuit should take a small amount of time to dissipate the remaining current.
 
  • #3
phyzguy
Science Advisor
4,716
1,638
If the inductance in the circuit were truly zero, the current would vanish instantly. However, all real circuits have some inductance, so the current will decay with a time constant given by L/R.
 
  • #4
perplexabot
Gold Member
329
5
Alright, so assuming the circuit has zero inductance (which is what I think my physics book is doing) then the current will immediately stop after the switch is opened. Thanks.
 

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