# Rate of Field Change for Induced Current of Loop

1. Feb 21, 2012

### tevatron1

1. The problem statement, all variables and given/known data

A single conducting loop of wire has an area of 8.0×10−2 m^2 and a resistance of 110 Ω. Perpendicular to the plane of the loop is a magnetic field of strength 0.37 T.

At what rate (in T/s) must this field change if the induced current in the loop is to be 0.33 A?

2. Relevant equations

Trying to solve for ΔB/Δt

3. The attempt at a solution

We have a change in magnetic flux, but it seems to be due to ΔB rather than ΔA, so Δflux = ΔB*Acosθ (However since cos(90) = 0, I'm not sure if this will be correct).

Using Faraday's Law |ε| = N|(Δflux/Δt)|
Substituted Δflux = ΔB*A into Faraday's Law --> ε = N(ΔB*A/Δt)
Substituted the equation for the induced EMF into I = |ε|/R and solved for ΔB/Δt
ΔB/Δt = I*R/A (N=1 because the loop has 1 turn)

453.75 T/s = (.33A)*(110Ω)/(8.0*10^-2 m^2)

I'm not sure where I'm going wrong...
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Feb 21, 2012

### kushan

θ would not be 90 as Area vector and B make 0 angle

3. Feb 21, 2012

### tevatron1

Okay, then cos(0) = 1, which would prove that my assumption Δflux = ΔB*A*cos(0) = Δflux = ΔB*A

How does the rest of my thought process look?

4. Feb 21, 2012

### kushan

as as i know you are doing correctly ,
where are you stuck ?

5. Feb 21, 2012

### tevatron1

Mastering Physics tells me this is the wrong answer, though it does not give any explanation as to why.

6. Feb 21, 2012

### kushan

what is " mastering physics "

7. Feb 21, 2012

### tevatron1

It's the online website for our physics homework. When you enter your answer, you are told whether or not your answer is correct. You are given 5 attempts, during which the points you earn diminish.

8. Feb 21, 2012

### kushan

Even I am in confusion as they have given magnitude of magnetic field
(which means a constant field ) but asking find at what rate it would vary

9. Feb 21, 2012

### tevatron1

Yes, I noticed this as well. I purposely left that out of my equation as we are attempting to solve for ΔB/Δt. I assume it's the authors of the homework trying to trick us into thinking the value is necessary. Though I cannot see how it could be.

10. Feb 21, 2012

### kushan

I am sorry as I fail to help you further with this problem

11. Feb 21, 2012

### technician

You know the resistance of the loop and you know the current so you should be able to find the induced emf

12. Feb 21, 2012

### tevatron1

"I am sorry as I fail to help you further with this problem "

Thanks, Kushan. I appreciate your help. I think there might be an issue with the website. It wouldn't be the first time.

Technician: You might notice that is exactly what I attempted to do... No worries though.

13. Feb 21, 2012

### tevatron1

As it turns out, the website wanted a different number of significant figures. Albeit, an incorrect number with the given information...

14. Feb 22, 2012

Thank god