Fig  shows L-shaped rod rotating about its end O

in a plane perpendicular to the magnetic field B. The part OA of the rod is non-conducting while the part AB is conducting. The induced e.m.f. between the ends A and B is

• A

  $\frac{1}{2}{\mathrm{\omega BL}}^2$

• B

  ${\mathrm{\omega BL}}^2$

• C

  $2{\mathrm{\omega BL}}^2$

• D

  $\frac{1}{2}{\mathrm{\omega B}}^2\mathrm{L}$