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

Current in the inner coil `i=(e)/(R )=(A_(1))/(R_(1))(dB)/(dt)`
Length of the inner coil=`2pia`
So its resistance `R_(1)=50xx10^(-3)xx2pi(a)`
:. `i_(1)=(pia^(2))/(50xx10^(-3)xx(2pib))xx0.1xx10^(-3)`
`=2xx10^(-3)=2xx10^(-4)A(CW)`