A uniform horizontal magnetic field B exists in the region A B C D. A rectangular loop of mass m and horizontal side / and resistance R is placed in the magnetic field as shown in fig.(4). With what
velocity should it be pushed down so that it continues to fall without acceleration ?

• A

  $\frac{\mathrm{mgR}}{{\mathrm{B}}^2{\mathrm{l}}^2}$

• B

  $\frac{{\mathrm{B}}^2{\mathrm{l}}^2}{\mathrm{mgR}}$

• C

  $\frac{\mathrm{mg}}{\mathrm{BlR}}$

• D

  $\frac{\mathrm{RBl}}{\mathrm{mg}}$