Question 1202085
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This question is more suited to physics homework sites (eg: physicsforums.com) but the basic idea is this:
A moving current through a coiled wire causes a magnetic field, which interacts with the earth's magnetic field. 


Further Reading
<a href = "https://www.khanacademy.org/science/physics/magnetic-forces-and-magnetic-fields/magnetic-flux-faradays-law/a/what-is-faradays-law">https://www.khanacademy.org/science/physics/magnetic-forces-and-magnetic-fields/magnetic-flux-faradays-law/a/what-is-faradays-law</a>
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