A tangent galvanometer has 66 turns and the diameter of its coil is 22cm. It gives a deflection of `45^@ for 0.10 ` A current. What is the value of the horizontal component of the earth's magnetic field?

Explanation

For a tangent galvanometer `I = K tantheta`
`= (2r B_H)/(mu_0 n) tantheta`
or, `B_H = (mu_o ni)/(2r tantheta)`
`= ((4pi xx 10^(-7) Tm/A) xx 66 xx (0.1 A))/((22 xx 10^(-2) m) (tan 45^@))`
`= 3.8 xx 10^(-5) T`