Plane figures made of thin wires of resistance `R=50` milliohm//metre are located in a uniform magnetic field perpendicular into the plane of the figures and which decrease at the rate `dB//dt=0.1 mT//s`. Then currents in the inner and outer boundary are. (The inner radius `a=10 cm` and outer radius `b=20cm)`

Options

A. `10^(-4)A` (Clockwise), `2xx10^(-4)` A (Clockwise)
B. `10^(-4)A` (Anticlockwise), `2xx10^(-4)` A (Clockwise)
C. `2xx10^(-4)A` (clockwise), `10^(-4)` A (Anticlockwise)
D. `2xx10^(-4)A` (Anticlockwise), `10^(-4)` A (Anticlockwise)

Answer

A

Explanation

`i_(1)=e/R_(1)=A_(1)/R_(1)((dB)/dt)`
`R_(1)=50xx10^(-3)xx2pia`
`thereforei_(1)=(pia^(2))/(50xx10^(-3)xx2pia)xx0.1xx10^(-3)=10^(-4)` A (cw)
(direction is clockwise)
`i_(2)=(pib^(2))/(50xx10^(-3)xx2pib)xx0.1xx10^(-3)=2xx10^(-4)A`
(direction is clockwise).