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**1. Homework Statement**

##N=2.5\times 10^3## wire turns are uniformly wound on a wooden toroidal core of a very small cross-section. A current ##I## flows through the wire. Find the ratio ##\eta## of the magnetic induction inside the core to that at the centre of the toroid.

**2. Homework Equations**

**3. The Attempt at a Solution**

The field inside the core has some finite value and at the centre it is zero. So the ration should be infinite but this wrong. I don't see what I have missed.