# Change in flux

1. Homework Statement

A flexible, circular conducting loop of radius 0.15m and resistance 4 ohms lies in a uniform magnetic field of .25 T. the loop is pulled on opposite sides by equal forces and stretched until its enclosed area is essentially zero m^2. it takes .30s to close the loop. what is the change in flux? 2. Homework Equations

3. The Attempt at a Solution

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since there are no details on the change in area with respect to time (i.e. you don't know exactly how the area changes as it bends from the 2 forces) it seems like a simple estimate using final - initial

$$B\frac{A_F-A_i}{t_F-t_i}$$

ideasrule
Homework Helper
The change in flux doesn't depend on time. It's just the final BA minus the initial BA.

Thanks for the quick response!

I'm not say either of you guys are wrong but I tried both equations and I got two different answers.

The first equation got me .01767 but when i plug this into Faraday's equation I get -0.0589 volts

The second equation got me -0.0589 Wb.

Which one is correct?

Thanks for the quick response!

I'm not say either of you guys are wrong but I tried both equations and I got two different answers.

The first equation got me .01767 but when i plug this into Faraday's equation I get -0.0589 volts

The second equation got me -0.0589 Wb.

Which one is correct?
i accidentally told you how to find the change in flux with respect to time (I saw you mention faraday's law and it set me on that track)

If the problem is only asking for the change in flux, do what ideasrule said:
B(A_f - A_i)

sorry about setting you off on the wrong track.

haha no it's ok no big deal. Thanks again!!