Induced emf at a specific time

  • #1

Homework Statement




A circular coil with 35 turns of wire and a diameter of 19 cm is placed in a magnetic field given by B(t) = 6 t^2 + 6 t + 2 T where t is time in seconds. The field is perpendicular to the plane of the coil. What is the induced EMF at t = 5 s?

Homework Equations




E=-d(magnetic flux)/dtime

The Attempt at a Solution


I found E to be 36.12 V but that's wrong. I'm not sure what's wrong. I did E=NAB/time.
 
Last edited:

Answers and Replies

  • #2
1,187
5
Emf is proportional to negative the derivative or rate of change of the magnetic flux with respect to time. The area is constant, thus
V = -NA*dB/dt.
 
  • #3
I plugged in -36.12 but it's still wrong. Can we have a negative voltage?
 
  • #4
Could you please tell me where I'm wrong? I have a couple of hours left.
 
  • #5
1,187
5
dB/dt = 12t + 6; at t = 5s, dB/dt = 66T/s
N = 35 turns
A = pi*r^2...so your problem might be that you're using the diameter of 19cm instead of the radius; also, be sure that you convert the given units to the proper units, so the radius = d/2 = 9.5cm = .095m.
The emf is V = -NA*dB/dt....and you could have a negative voltage.
 
  • #6
Thank you very much I appreciate it.
 

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