A straight wire of length 50 cm carrying a current of 2.5 A is suspended in mid-air by a uniform magnetic field of 0.5 T (as shown in figure). The massof the wire is (`g = 10 ms^(-2)`)

Options

A. 100 gm
B. 125 gm
C. 62.5gm
D. 250 gm

Answer

C

Explanation

`:' l = 50 cm, I = 2.5 A, B -0.5 T`
Magnetic field `vec B` exerts force on straight wire given by `vec F = Ivecl xx vec B`
It is clear from the above expression that this force will act vertically upwards.
For mid-air suspension, this must be balanced by the force due to gravity. `:. "Weight of wire" = "force exerted by magnetic field"`.
`mg= IlBsin90^(@)`
`m= (IlB xx 1 )/(g)= (2.5 xx 0.5 xx 0.5)/(10)= 625 xx 10^(-4) kg= 62.5 g`