A loosely wound helix made of stiff wire is mounted vertically with the lower end just touching a dish of mercury. When a current from the battery is started in the coil through the mercury
the wire oscillates
he wire continues making contact
the wire breaks contact just when the current is passed
the mercury will expand by heating due to passage of current
When a current is passed through the helix, the neighbouring coils of the helix attract each other due to which it contracts. As a result the contact is broken and the coils will recover their original state under the influence of a restoring force. The contract is made again and the process continues. Thus, the wire oscillates. Hence the correct choice is (a).
Study 40% syllabus and score up to 100% marks in JEE