Question

When direct current passed through a spring then it:
(A) Contracts
(B) Expands
(C) Uncharged
(D) Vibrate

Answer 1

Hint When a current is passed through a circular coil then circular coil starts behaving like a magnet. Spring is like a combination of circular coils and when current passes through the spring each coil behaves like a magnet and spring also behaves like a strong magnet.

Complete step by step solution
When a current is passed through a circular coil then the circular coil starts behaving like a magnet. Spring is like a combination of circular coils. When current is passed through the spring each coil of spring behaves as individual magnets.
Here given current is direct current means current always flows in the same direction and magnetic polarity of each coil remains the same. Here all coils have the same polarity.
Due to the same polarity south of a coil faces toward the north pole of the next coil or north pole of a coil faces toward the south pole of the next coil. And because unlike polarity all coils attract each other means the gap between two coils or circular ring of spring decreases.
So, the spring contracts when direct current is passed through it.

Hence the correct answer is option A.

Note When we pass an alternative current through a metallic spring it starts oscillating due to change in direction of flow of current and increase and decrease in current. If we place a paramagnetic substance inside the spring and pass direct current through it, it starts behaving as a strong magnet and this magnet is called an electromagnet.