# EMF problem

#### kone

Joined Nov 19, 2006
5
Can anyone help me with this problem?

I have calculated the answer but I am not confident that it is correct.

"Calculate emf generated in a current-carrying coil of 500 turns and cross-sectional area 5cm2 when a flux density of 0.2T density in it is reversed (changed to the opposite polarity) in a time of 10ms."

My understand is as follows.

If Flux Density = Flux/Area Then Flux = Area * Flux Density

Therefore .2T = Flux/5cm2 Then Flux = (.0005m2) * .2T which is .0001wb

so Intial Flux = .0001wb

Then flux density is changed to opposite polarity, am I right in thinking 0.2T becomes -0.2T?

If so then Flux Density = Flux/Area Then Flux = Area * Flux Density

So -.2 = Flux/5cm2 Then Flux = (.0005m2) * -.2 which is -.0001wb

Then Final Flux = -.0001wb

Then using lenz law

-500(-.0001 -.0001)/.01

-500 (-.0002)/.01

= .1/.01

= 10V

10V seems to high to me......

Any help would be greatly appreciated,

Kone