A straight wire of length `30 cm` and mass `60 mg` lies in a direction `30^(@)` east of north.The earth's magnetic field at this is horizontal and has a magnitude of `0.8 G`.What current must be passed through the wire,so that it may float in air ?

Options

A. `10A`
B. `60A`
C. `50A`
D. `20A`

Answer

C

Explanation

As shown in figure, if a current i is passed through the wire from end A towards B it will experience a force Bi L `sintheta` vertically up and hence will float if

`Bilsintheta=mg`
i.e., `i=(mg)/(Blsintheta)`
`=(60xx10^(-6)xx10)/(0.8xx10^(-4)xx30xx10^(-2)xx1//2)=50A`