# physics

A length of wire carrying a current i and bent into a circular coil of one turn.The same length of wire has been out to give a coil of 5 turns, each of 1\5 the original radius.If Ba and Bb are the magnitudes of the magnetic fields at the centers of the two coils, what is the ratio Bb\Ba?

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1. The formula you need can be found here:
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/curloo.html#c2

Multiply it by N if there are N loops.

Since the field at the center is inversely proportional to R, The field increases by N^2 . The ratio is 25.

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