# Magnetic Field Protractor

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## Homework Equations

R = ρ (l/A)
I = ε/R
s = rθ
Magnetic flux = Integral(B ⋅ dA)

## The Attempt at a Solution

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I managed to solve parts (a) and (b) independently. Here is my work for those two parts:

My real issue is with part (c) which uses the answers from (a) and (b). I have absolutely know idea how to solve part c, except that it involves in some way the formula Magnetic flux = Integral(B ⋅ dA)

Homework Helper
Gold Member
Be careful with converting mm2 to m2.

So far, you have not mentioned the basic law of electromagnetism that accounts for the induced current in the circuit.

Be careful with converting mm2 to m2.

So far, you have not mentioned the basic law of electromagnetism that accounts for the induced current in the circuit.

Yes, You're right. That law goes as follows:

ε = - the rate of change of flux (sorry I do not know how to write this in the proper notation)

And the induced current is found, simply, through Ohm's law: ε = iR

So how can I, with this, go about part (c)?

Homework Helper
Gold Member
ε = - the rate of change of flux
How do you find the rate of change of a quantity. What mathematical operation is involved?

How do you find the rate of change of a quantity. What mathematical operation is involved?

Take the derivative. So I can take the derivative of part (b). But theta needs to be expressed in terms of the time, t?

Homework Helper
Gold Member
Yes.