Question

A simple pendulum of mass m charged negatively to q coulomb oscillates with a time period T in a downward electric field E such that mg > qE. If the electric field is withdrawn, the new time period :

• A. $=$T
• B. $>$T
• C. $<$T
• D. any of the above three is possible

Answer 1

The correct option is C $<$T

Time period in the absence of electric field $T^{\prime }=2\pi \sqrt{\frac{l}{g}}$
In the presence of electric field
$g_{eff}=(mg-qE)/m$
Therefore $T=2\pi \sqrt{\frac{l}{(mg-qE)/m}}$
$T^{\prime }=2\pi \sqrt{\frac{l}{g}}$
or $T^{\prime }<T$