Question

Motion of a moving electron is not affected by
A . An electric field applied in the direction of motion
B . Magnetic field applied in the direction of motion
C . Electric field applied perpendicular to the direction of motion
D . Magnetic field applied perpendicular to the direction of motion

Answer 1

Hint: In this question we have to study the behaviour of an electron having velocity in different conditions like when an electric field or a magnetic field is applied in the direction of motion or perpendicular to the direction of motion of the electron. A force is experienced by a charged particle moving with a certain velocity in an electric field as well as magnetic field.


Formula used:
Magnetic force on the particle:
${F_m}$= q(v×B);
Here, q denotes the charge, v is the velocity of the particle, and B the magnetic field.
Electric force on the particle:
${F_e}$= qE;
Here, q denotes the charge, and E the electric field.

Complete answer:
The Electric force on the particle is:
Fe= qE;
Electric force has no dependence on the magnitude or direction of the velocity. Therefore if a charged particle enters an electric field, it will experience a force of magnitude qE.
The magnetic force acting on a charged particle in a magnetic field is:
${F_m}$=q(v×B)
Since there is a cross product of velocity and magnetic field, if the velocity of the particle and magnetic field are in the same direction then there will be no magnetic force working on the particle. But if the velocity of the particle is perpendicular to the direction of the magnetic field, ${F_m}$ = qvB, which is the maximum force that can be experienced by that particle.
Therefore, motion of a moving electron is not affected by magnetic field applied in the direction of motion
The correct answer is B.




Note:An electric field accelerates both moving and stationary charges. Only a moving charge, though, is accelerated by a magnetic field. Because the magnetic force is always perpendicular to the particle's motion, the charged particle is not affected by it.
The inertial frame of reference and velocity are both dependent on the magnetic force. Charged particle subjected to magnetic force, F=q(v×B) or F=qvBsinθ.
As a result, the magnetic force depends on velocity. From one inertial frame to the next, it is different.