Question

An electron moves on a straight line path XY as shown. The abcd is a coil adjacent to the path of the electron. What will be the direction of current, if any, induced in the coil?

A. The current will reverse its direction as the electron goes past the coil
B. No current induced
C. abcd
D. adcb

Answer 1

As we know that, the directions of the electron flow and the current are opposite to each other, thus, the direction of the magnetic field will be in the direction of the electron flow.The direction of current induced is such that it always opposes the change or cause.

Complete answer:
We know that, generally, the direction of the flow of electrons is always in the opposite direction to that of the direction of the flow of current. As shown in the figure, the electron is moving from the direction X to Y, thus, the current will be flowing in the direction Y to X.
Now, let us consider the production of the magnetic field around the coil abcd.Before the start of the flow of the current, the magnetic field around the coil abcd will be zero. When the electron starts to move from the direction X to Y, the current starts to flow from the direction Y to X.
Thus, as the current starts to flow near the coil abcd, the magnetic field gets induced and starts to increase, till the flow of current reaches the point ‘c’ of the coil or the mid-point of the path XY. As, in the beginning, the magnetic field induced flows in the downward direction, to resist this change the current starts to flow in the direction of a – b – c – d of the coil abcd.

Once, the current crosses the midpoint of the path XY, the magnetic field starts to decrease. Again, in order to resist this change in the magnetic field, the current starts to flow in the direction of a – d – c – b of the coil abcd. So, the current reverses its direction, as the electron starts to move away from the coil.
As the current reverses its direction, as the electron goes past the coil.

So, the correct answer is “Option A”.

Note:
According to the thumb rule, in the beginning, the direction of the magnetic field will be the downward direction, as the current starts to flow from the left direction that is, from the a-b-c-d. Again using the same thumb rule, in the end, the direction of the magnetic field will be the upward direction, as the current starts to flow from the right direction that is, from the a-d-c-b.