A circular coil of 5 turns and of 10 cm mean diameter is connected to a voltage source. If the resistance of the coil is `10Omega`, the voltage of the source so as to nullify the horizontal component of earth's magnetic field (H=0.314gauss)`, at the center of the coil should be

Options

A. 6.5 V, plane of the coil normal to magnetic meridian
B. 2.5 V, plane of the coil normal to magnetic meridian
C. 6.5 V, plane of the coil along the magnetic meridian
D. 2.5 V, plane of the coil along the magnetic meridian

Answer

A

Explanation

Magnetic field of 1 A turn/m
`=4pixx10^(-7)T`
Field at centre `B=(mu_(0)NI)/(2r)`
`=(mu_(0)N)/(2r)xx(V)/(R )`
or `V=(2rRB)/(mu_(0)N)`
`therefore B=(2xx(5xx10^(-2))xx10xx(30xx4pixx10^(-7)))/((4pixx10^(-7))xx5)`
or `V=6` volt
To nullify the horizontal component of magnetic field of earth, plane of the coil should be normal to magnetic meridian.