A horizontal wires is free to slide on the vertical rails of a conducting frame as shown in figure. The wire has a mass m and length `l` and the resistance of the circuit is R. If a uniform magnetic field B is directed perpendicular to the frame, then find the terminal speed of the wire as it falls under the force of gravity.
| A. |
`(mgR)/(B^2l^2)` |
 |
| B. |
`(mg)/(Bl)` |
| C. |
`(2mgR)/(B^2l^2)` |
| D. |
0 |