Q. 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 a battery is started in the coil through the mercury
A) The wire oscillates
B) The wire continues making contact
C) The wire breaks contact just as current is passed
D) The mercury will expand by heating due to passage of current
Explanation
(a) When current is passed, the spring will contact, breaking the contact with mercury. As contact is broken, magnetic effects become zero. Due to weight the coil will restore its contact with mercury and so on. The coil will have oscillatory behavior.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.