There are 50 turns per cm length in a very long solenoid. It carries a current of 2.5A. The magnetic field at its centre on the axis is ______ T.

Options

A. `(mu_(0)I)/4(r_(1)+r_(2))`
B. `(mu_(0)I)/4(r_(1)+r_(2))`
C. `(mu_(0)I)/4((r_(2)+r_(1))/(r_(1)r_(2)))`
D. `(mu_(0)I)/4((r_(2)-r_(1))/(r_(1)r_(2)))`

Answer

C

Explanation

The magnetic field at the centre of two semicircular conducting wires is in the perpendicular and inside plane of paper.
`B_("net")=B_(1)+B_(2)=(mu_(0)I)/(4r_(1))+(mu_(0)I)/(4r_(2))=(mu_(0)I)/4((r_(1)+r_(2))/(r_(1)r_(2)))`