A brilliant student of physics developed a magnetic balance to weight objects. The mass `m` to be measured is hung from the center the bar. Bar is kept in a uniform magnetic field of `1.5 T` directed into the plane of the figure. Battery voltage can be adjusted to vary the current in the circuit. The horizontal bar shown is `60cm` long and is made of extremly light weight material. It is connected to the battery via a resistance. There is no tension in the supporting wired. The magnetic force only supports the hanging weight.

If `V = 150 V`, what is the maximum mass `m` ?

Options

A. (a) `1.3 kg`
B. (b) `1.8 kg`
C. (c ) `2.2 kg`
D. (d) `2.7 kg`

Answer

D

Explanation

(d) Current should enter the bar from `P` so that magnetic force is upward.
`ilB = mg or (V)/(5)lB = mg`
or `m = (150 xx 0.6 xx 1.5)/(5 xx 10) = 2.7 kg`