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## Homework Statement

A wire loop of area 2·0×10−4 m

^{2}

contains 40 turns, and has a total resistance of

40Ω. The plane of the loop is perpendicular to a uniform magnetic ﬁeld of magnitude

B

_{0}. The magnetic ﬁeld is now turned oﬀ such that the ﬂux through the loop drops

linearly to zero. A total charge 4·0 ×10−6 C passes around the loop. Determine B

_{0}.

## Homework Equations

None given

## The Attempt at a Solution

Ok so I think that

Emf=-N[itex]\frac{d\Phi}{dt}[/itex]

but it says that the field drops linearly so that just becomes

Emf=-NA[itex]\frac{\Delta B}{\Delta t}[/itex]

Also Emf=IR

So from this I equated the two but I will just end up with an expression for B

_{0}dependent on t, and I'm not sure if this is what is wanted. I'm unsure about my use of Ohm's law here too. Thanks in advance, any help at all would be great.