The wire loop PQRSP formed by joining two semicircular wires of radii $R_1$ & $R_2$ carries a current I as shown in the fig. The magnitude of magnetic field at the centre 'C' is
Answer & explanation
Correct answer: option 4
Magnetic Field due to semi circle QR , $ B_1 = \frac{\mu_0 I}{4R_1}$ Out of plane .
Magnetic Field due to semi circle SP , $ B_2 = \frac{\mu_0 I}{4R_2}$ In to the plane.
Net Magnetic field at the centre is $ B =\frac{\mu_0 I}{4}(\frac{1}{R_1} - \frac{1}{R_2}) $ Out of plane.