# A coil having N turns is wound tightly in the form of a spiral with inner and outer radii a and b respectively. When a current I passes through the coil, the magnetic field at the centre is Option 1)       Option 2)   Option 3)   Option 4)

As we learnt in

Magnetic Field due to Circular Current at the centre -

If a coil of radius r is carrying current i then magnetic feild at a distnace X from its centre is:

- wherein

Consider a small thickness dx at distance x from centre.

Number of turn in

Option 1)

incorrect

Option 2)

incorrect

Option 3)

correct

Option 4)

incorrect

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