If an observer is moving with respect to stationary electron then he observe
A. Only magnetic field
B. Only electric field
C. Both (a) and (b)
D. None of the above

Hint: When charge is at rest then it produces the electric field. A moving charge constitutes the electric current and electric current shows magnetic effect.

Complete step by step solution:
As we know that the motion is determined based on the frame of reference. A body is said to be in motion if the relative position of the body changes with respect to time when measured in a frame of reference.

For instance a passenger in a bus is at rest with respect to the fellow passenger in the bus, but it is in motion when it is observed from an observer standing at rest outside the bus.
In the same way, when the observer is moving with respect to the stationary electron then the electron is also in motion with respect to the observer.

So, when we observe the motion of the electron in a moving frame of reference the electron seems to be in motion. The observer will observe the magnetic field due to motion of charge with respect to the observer’s frame of reference. Hence, the observer will observe both the magnetic field as well the electric field when he is moving with respect to the stationary electron.

Therefore, the correct option is C.

Note: The magnetic field is not the characteristic of the motion of charge. As we know that the electric field is the function of distance from the charge. As the observer is moving with respect to the charge so the distance from the charge changes and so the electric field. The changing electric field produces the magnetic field.