The bob of simple pendulum is hanging vertically down from a fixed identical bob by means of a sting of length $l$. If both bobs are charged with a charge $q$ each, time period of the pendulum is : (ignore the radii of the bobs)

• A

  $2 \pi \sqrt{\frac{l}{g+\left(\frac{q^2}{l^2 m}\right)}}$
• B

  $2 \pi \sqrt{\frac{l}{g-\left(\frac{q^2}{l^2 m}\right)}}$
• Correct answer
  C

  $2 \pi \sqrt{\frac{l}{g}}$
• D

  $2 \pi \sqrt{\frac{l}{g-\left(\frac{q^2}{l}\right)}}$

Hence, the correct answer is option: 'C'.