A straight horizontal conducting rod of length `0*60m` and mass of `60g` is suspended by two vertical wires at its ends. A current of `5*0A` is set up in the rod through the wire. (a) What magnetic field should be set up normal to the conductor in order that the tension in the wire is zero?
(b) What will be total tension in the wires if the direction of current is reversed, keeping the magnetic field same as before (Ignore mass of the wire), `g=10ms^-2`.

Explanation

Here, `l=0*60m`,
`m=60g=60xx10^-3kg, I=5*0A`
(a) Tension in the wire is zero if the force on the wire carrying current due to magnetic field is equal and opposite to the weight of wire, i.,e,
`BIl=mg`
or `B=(mg)/(Il)=((60xx10^-3)xx10)/(5*0xx0*60)=0*20T`
The force on the conductor due to magnetic field will be upwards if the direction of magnetic field is horizontal and normal to the conductor.
(b) When direction of current is reversed, `BIl` and `mg` will act vertically downwards, the effective tension in the wires,
`T=BIl+mg`
`=0*2xx5*0xx0*60+(60xx10^-3)xx10`
`=1*2N`