The earth's magnetic field at a given point is `0.5xx10^(-5) Wb-m^(-2)`. This field is to be annulled by magnetic indcution at the centre of a circular conducting loop of radius `5.0 cm`. The current required to be flown in the loop is nearly

Options

A. `0.2 A`
B. `0.4 A`
C. `4 A`
D. `40 A`

Answer

B

Explanation

(b) Magnetic field at the centre of a circular loop carrying current `I` is given by
`B = (mu_(0) I)/(2 r)`
Where `r` is radius of circular loop.
`I = (B. 2 r)/(mu_(0))`
Given, `B = 0.5 xx 10^(-5) Wb//m^(2), r = 0.5 m`
`implies I = (0.5 xx 10^(-5) xx 0.1)/(4 pi xx 10^(-7)) ~~ 0.4 A`