The figure shows a conducting circular loop of radius 50 cm is placed in a uniform, perpendicular magnetic field 4 T. A metal rod OA is pivoted at the centre O of the loop. The other end A of the rod touches the loop. The rod OA and loop are resistanceless but a resistor having a resistance 5 Ω is connected between O and a fixed point C on the loop. The rod OA is made to rotate anticlockwise at a uniform angular speed 20 rad/s by an external force. Find the external torque (in Nm) needed to keep the rod rotating with the constant angular velocity of 20 rad/s.(Give only integer value)

The figure shows a conducting circular loop of radius 50 cm is placed

1.	The figure shows a conducting circular loop of radius 50 cm is placed in a uniform, perpendicular magnetic field 4 T. A metal rod OA is pivoted at the centre O of the loop. The other end A of the rod touches the loop. The rod OA and loop are resistanceless but a resistor having a resistance 5 Ω is connected between O and a fixed point C on the loop. The rod OA is made to rotate anticlockwise at a uniform angular speed 20 rad/s by an external force. Find the external torque (in Nm) needed to keep the rod rotating with the constant angular velocity of 20 rad/s.(Give only integer value)
Answer» The figure shows a conducting circular loop of radius $50 cm$ is placed in a uniform, perpendicular magnetic field $4 T .$ A metal rod $OA$ is pivoted at the centre $O$ of the loop. The other end $A$ of the rod touches the loop. The rod $OA$ and loop are resistanceless but a resistor having a resistance $5 Ω$ is connected between $O$ and a fixed point $C$ on the loop. The rod $OA$ is made to rotate anticlockwise at a uniform angular speed $20 rad/s$ by an external force. Find the external torque $(in Nm)$ needed to keep the rod rotating with the constant angular velocity of $20 rad/s$ . (Give only integer value)