A 1m long thin metal bar of negligible resistance weighing 1 kg rests on two metal supports as shown in the figure. The supports are connected in series to an ideal cell and a resistance. A uniform magnetic field 0.5T is applied in the region normal to the plane of the paper and into the paper. Maximum emf that the cell can have without breaking the circuit in volt is (g = $10{\mathrm{m}}^2$)

Given data:

Length L=1m

Magnetic field B=0.5 T

Resistance weight =1 kg

Acceleration g=10 m/s

Concepts of moving charges and magnetism

Explanation

The magnetic force acting on a body

F=BIL

The maximum force at which the magnet leaves the bar is only when the bar is about to leave the left side. Meanwhile, the force produced by the magnet is equal to the force produced by gravity and the upward force of the support, and the direction is opposite. 

F=mg

Both forces are equal

BIL=mg

$0.5\times I\times 1=1\times 10$

I=20 A

Therefore the maximum emf of the voltage is

$$\begin{gathered} V=IR \\ V=20\times 25 \\ V=500 V \end{gathered}$$