In Millikan's oil drop experiment an oil drop carrying a charge Q is held stationary by a potential difference \[2400\,V\] between the plates. To keep a drop of half the radius stationary the potential difference had to be made \[600\,V\]. What is the charge on the second drop [MP PET 1997]

• A.                    \[\frac{Q}{4}\]
• B.                                      \[\frac{Q}{2}\]
• C.                    \[Q\]
• D.                                      \[\frac{3Q}{2}\]