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Faraday's Law help, not sure if I'm using the equations correctly.

  • Thread starter beanus
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  • #1
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Homework Statement



A coil 3.55 cm radius, containing 480 turns, is placed in a uniform magnetic field that varies with time according to B = (1.20e-2 T/S)t + (3.05e-5 T/s[itex]^{4}[/itex] )t[itex]^{4}[/itex]. The coil is connected to a 620 Ohm resistor, and its plane is perpendicular to the magnetic field. You can ignore the resistance of the coil.

Homework Equations



[itex]\Phi[/itex][itex]_{B}[/itex]=BA
ε = - [itex]\frac{\Phi_{B}}{t}[/itex]

The Attempt at a Solution



First I divided by t and removed a t from each term in "B"

r = .0355
N = 480

A = [itex]\pi[/itex](.0355)[itex]^{2}[/itex] = 3.959192142e-3
AN = (3.959192142e-3)(480) = 1.900412228

So all we're left with is:
BAN = 1.900412228 [(1.20e-2 T/S) + (3.05e-5 T/s[itex]^{3}[/itex] )t[itex]^{4}[/itex]]

ε = (2.28e-2 V) + (5.80e-5 V/s[itex]^{3}[/itex])t[itex]^{3}[/itex] should be my final answer but mastering physics says I'm wrong. Please help thanks!

EDIT:

I just found a posting where they multiplied the second term in B (3.05e-5 T/s[itex]^{3}[/itex] )t[itex]^{4}[/itex] by 4. When I did that I got the correct answer! But I don't know why I would multiply the term by 4. Any thoughts?
 
Last edited:

Answers and Replies

  • #2
1,506
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I have not checked all of your maths but did you remember to x4 when you differentiated t^4 ??
 
  • #3
Redbelly98
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ε = - [itex]\frac{\Phi_{B}}{t}[/itex]
[tex]ε = -\frac{d \Phi_{B}}{dt}, \ \text{ not } \ - \frac{\Phi_{B}}{t}[/tex]
 

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