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# re: search coil calculation

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#### lemonz

##### New Member
Hi:
I have done a calculation but it seems really high.

I have a 5000 turn search coil - area 3.6 cm^2 - which is used to measure flux density between poles of horeshoe magnet. Flux density is 0.80T, and the coil is pulled out of the field in 0.24s.

I calculated the e.m.f. at:

5000 x 0.80T / 0.24s = 16666.667 V

Can someone help me to understand what I have done wrong please?
thanks

Have a look at Faraday's Law

You don't seem to have included the coil area in your calc.

Hi:
I have done a calculation but it seems really high.

I have a 5000 turn search coil - area 3.6 cm^2 - which is used to measure flux density between poles of horeshoe magnet. Flux density is 0.80T, and the coil is pulled out of the field in 0.24s.

I calculated the e.m.f. at:

5000 x 0.80T / 0.24s = 16666.667 V

Can someone help me to understand what I have done wrong please?
thanks

You have considered the flux density rather that the change in flux with respect to time which is what dΦ/dt is in the equation emf=-N*dΦ/dt.

The flux density needs to be multiplied by the area over which you are concerned. The area will be changing as you pull the coil out, so you need to work out the rate of change of flux based on this. After 0.24s the area will be zero as the coil will have been removed.

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