$A$ wheel of $20$ metallic spokes, each $40 \text{ cm}$ long, is rotated with a speed of $180 \text{ rev/min}$ in a plane normal to the horizontal component of Earth's magnetic field $H_{e}$ at a place. If $H_{e} = 0.4 \text{ G}$ at that place, the induced emf between the axle and the rim of the wheel is:

• A
  $192 \pi \times 10^{-7} \text{ V}$
• B
  $256 \pi \times 10^{-7} \text{ V}$
• C
  $148 \pi \times 10^{-7} \text{ V}$
• D
  $110 \pi \times 10^{-7} \text{ V}$