Question

Which of these points may be a null point?

A. A
B. B
C. C
D. None of these

Answer 1

Hint: Null point in any aspect is a point where the value of that particular quantity is zero. This value of that particular quantity is zero due to the fact that the two or more opposite quantities cancel each other. So here we will observe each point accordingly.

Complete step by step answer:
At each point we will analyse and compare the value of the electric field and will search for the point where the electric field will be zero.
At point $A$ we see the amount of the electric field lines due to left charge is more than the charge situated in the right so the effect of the electric at point $A$ is mainly due to the charge situated in the left and the effect of the electric field situated in the right is negligible, so at point A the value of the electric field will not be zero.
Same thing happens for the point $B$, here also the effect of the electric field is only due to the charge situated at the right and the effect of the field generated due to charge situated at left will be negligible. So, the value of the electric field at point $C$ will not be zero.
Now for the point $C$ we see that this point is situated exactly in between the two charges. So the two charges will provide the same effect on the point $C$and the value of electric field produced by both charges at point $C$ will be of the same magnitude and opposite in direction, hence they will cancel each other and the effective value of the electric field at point $C$ will be zero.
Hence point $C$ is the null point.

So, the correct answer is “Option C”.

Note: Here we have discussed the electric lines of force. Some of the properties related to the electric lines of force are as follows,
1. Electric lines of force will never intersect each other.
2. The electric lines of force ordinates from positive charge and terminates at the negative charge.
3. Tangent at any point on the line of force will give the direction of the electric field at that point of that particular line of force.