# How much current needed to cancel Earth's magnetic field [closed]

It can be shown the magnetic field in a long narrow tube that is 5 meters is uniform and given by $$B=1.26 \times 10^{-6} N I$$

where N is number of wire loops/meter. Assuming the solenoid is aligned along the Earth's magnetic field,how much current is needed to cancel the Earth's field? Earth's magnetic field is $10^{-4}$ Tesla

this is how i did it N=1000/5=200 I=(10^-4)/(1.26E-6)(200) I=0.396 A

Is that all there is to it? or am I missing another step

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I've added the homework tag because this is very basic and sounds like a homework question to me. We don't do your homework for you here, but if you edit the question to tell us what concepts are giving you trouble, and what you have already tried to do to solve the problem, we can help you with those concepts. – Colin K Jul 7 '12 at 20:43
Hi lily, and welcome to Physics Stack Exchange! Colin is right, we don't do homework questions with no work shown, or where you don't have a specific conceptual question about the problem. For this latest revision, if you have some reason to think your procedure is incorrect, then edit the question to ask about that and I'll be happy to reopen it. But since you have an answer and you're just looking for a second opinion on it, that's too localized for us. – David Zaslavsky Jul 8 '12 at 0:48

## closed as too localized by Colin K, Qmechanic♦, David Zaslavsky♦Jul 8 '12 at 0:48

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