The horizontal component of earth's magnetic field at a certain place is `3*0xx10^-5T` and the direction of the field is form the geographic south to the geographic north. A very long straight conductor is carrying a steady current of `1A`. What is the force per unit length on it when it is placed on a horizontal table and the diection of the current is (a) east to west (b) south to north?

Explanation

Here, `B=3*0xx10^-5T, I=1A`.
Force on current carrying conductor in magentic field is `F=BIl//sin theta`
Force per unit length, `f=F/l=BIsintheta`
(a) When current flows from east to west, then `theta=90^@`
`:. f=BI sin 90^@=(3*0xx10^5)xx1`
`=3xx10^-5Nm^-1`
(b) When current flows from south to north, then `theta=0^@`
`:. f=BI sin theta0^@=0`