The bob of a simple pendulum of length $l$ is made of iron. The pendulum is oscillating over a horizontal coil carrying a direct current. If the time period of the pendulum is $T$,then:

• A
  $T < 2\pi \sqrt{\frac{l}{g}}$ and damping is smaller than in air alone.
• B
  $T = 2\pi \sqrt{\frac{l}{g}}$ and damping is larger than in air alone.
• C
  $T > 2\pi \sqrt{\frac{l}{g}}$ and damping is larger than in air alone.
• D
  $T < 2\pi \sqrt{\frac{l}{g}}$ and damping is larger than in air alone.