What formula would I use for this?
A 10cm-radius, 25-loop circular wire coil with 40 ohms of resistance sits in a 50T magnetic field. Over the next eight seconds, the field strength is reduced by one-fifth.
If the field strength is reduced during a two-second time interval instead, how much current would flow in the coil?
Other information: 0.98V induced in the coil, 0.025A flows in the coil while the field is being reduced.

Question

What formula would I use for this?
A 10cm-radius, 25-loop circular wire coil with 40 ohms of resistance sits in a 50T magnetic field. Over the next eight seconds, the field strength is reduced by one-fifth. 
If the field strength is reduced during a two-second time interval instead, how much current would flow in the coil? 
Other information: 0.98V induced in the coil, 0.025A flows in the coil while the field is being reduced.

anonymous · Answer

You gotta use Faraday's law
$$emf = -L \frac{di}{dt}$$

anonymous · Answer

I am so sorry
It is
$$emf = -NA \frac{dB}{dt}$$

anonymous · Answer

So which of these numbers would I use? I get confused

irishboy123 · Answer

it's a really daft question.

they give you the answer to the first bit (or did you work that out? if so, it's right, BTW) , so the question really is this -- if you change the field strength 4 times as fast (ie over 8s rather than 2s), what does that do to the induced current and voltage, given previosu figures of 0.98V and 0.025A induced ?

do you know the answer to that?

anonymous · Answer

I worked out the first problems myself. But would I multiply the .025A by 4? And get .1A for my answer?

irishboy123 · Answer

yes, it's all happening 4x faster so go for it.

anonymous · Answer

It's right! Thank you!