Question

If a current is passed through a spring then the spring will:
A. Expand
B. Compress
C. Remain same
D. None of these

Answer 1

Hint: We will solve the given question according to the concept of current electricity and magnetism. Which states that when two parallel conductors which each carry current in the same direction will attract one another, while two such conductors which carry currents in an opposite direction will repel each other.

Complete answer:
As we know, when current is passed through a spring then the current flows parallel in the adjacent turns. And when two wires are placed parallel to each other then the current which flows is in the same direction, the wires attract each other. Similarly, in the given question the various turns attract each other and the spring will compress.
Now, for a better understanding spring can be assumed as a coil which is parallel to each other. Further, when the current flows in the spring then each coil gets current flow in the same direction. So, they are attracted to one another which in turn results in compression of spring.
Another factor which we encounter is that there exists a heating effect, but it's almost negligible as compared to the compression effect. Suppose a spring which is actually like a circular loop of many turns. Since the current flows in the same direction, even the direction of the magnetic field too will be in the same. So, dipole will be created on each loop, and they will attract each other. Which would further result in compression of the spring.
Thus, when a current is passed through a spring then the spring will get compressed.

Hence, option (B) is the correct answer.

Note:
There are few factors which are responsible for affecting the elasticity of a spring such as,
1) Diameter of the coils of a spring: Spring of a smaller diameter is known to be a stiffer spring.
2) Length: Spring made up of shorter length tends to be a stiff spring.
3) Thickness: Spring which is made up of a thick wire is said to be a stiff spring.