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Voltage across the inductor

  1. Jan 23, 2012 #1
    According to faraday's law the governing equation is emf=-d(flux)/dt.But we usually write the voltage across the inductor as v=d(flux)/dt.What happened to the minus sign?
  2. jcsd
  3. Jan 23, 2012 #2


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    If there's an inductor in series with a battery and you open the switch, the flux will be decreasing yet the voltage that appears across the inductor in a sense that will 'maintain' the current. I think that (Lenz's law) accounts for the choice of sign.
  4. Jan 23, 2012 #3
    It is used to indicate that the induced emf OPPOSES the change producing it.
    If you only need to calculate the magnitude is is common to drop the - sign
  5. Jan 24, 2012 #4
    Kirchhoff's law states the the sum of the voltage drops around the circuit must equal zero.
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