Question

pls do this question..!! ​

Answer 1

Answer:

(2)mgRsinθ/B²l²

Explanation:

Terminal velocity means the body moves with constant velocity even though forces are acting on it (due to nullification of force by each other).

Two forces  are acting on the wire namely, its weight and force produced due to magnetic field. The body moves with the terminal velocity (say v),only when they are equal.

If you observe the rod's motion it looks like motion of a body on an inclined plane. So a force of mgsinθ acts on it along the inclination(downwards).

Now due to motion of rod the flux entering the closed loop decreases and a motional EMF is developed. It is given by EMF=Blv(B-magnetic field, l-length of conductor, v-velocity of conductor){if you observe, the current is in anticlockwise direction and using Flemming's left hand rule the direction of force would be up the plane}

From Ohm's law(v=iR, v-EMF,i-current, R-resistance)

iR=Blv

i=Blv/R

Now there is a force due to flow of current and magnetic field, it is given by,

F=Bilsinθ(θ=90, since the field is perpendicular to current)

F=Bil

substitute the value of i

F=B²l²v/R

This force must be equal to mgsinθ since the body is moving with terminal velocity,

i.e mgsinθ=B²l²v/R

Therefore v=mgRsinθ/B²l²

Hence option(2) suits the answer.