Question

A coil having N turns is wound tightly in the form of a spiral with inner and outer radii a andb respectively. When current I passes through the coil, the magnetic field at the centre is –

• A. $\frac { \mathrm { N } \mu _ { 0 } \mathrm { i } } { 2 ( \mathrm {~b} - \mathrm { a } ) }$ log_e
• B. log_e
• C. log_e
• D. None of these

Answer 1

Answer: (A)

$\frac { \mathrm { N } \mu _ { 0 } \mathrm { i } } { 2 ( \mathrm {~b} - \mathrm { a } ) }$ log_e

Answer 2

Magnetic induction due to a circular current-carrying loop at x is dB =(dN)

Total magnetic field at the centre (due to all loops)

B =dN =dx

=log_e