Question

In a magnetic field pointing away from you, an electron travelling to the right will experience a force in the _______________ direction:
A) Horizontal
B) Upward
C) Downward
D) None of these

Answer 1

Hint
We can use the right-hand mnemonic called as the right-hand rule in the magnetic field to describe the direction of the magnetic force on a charged particle. It is based on the two given factors (i) magnetic field line direction and (ii) the direction of the movement of the charged particle.


Complete step by step answer
Whenever a charged particle moves through a magnetic field, it experiences a finite amount of force. After analyzing the phenomenon with experiments, scientists have come up with a right-hand mnemonics to describe the direction of the three interrelated quantities which plays the most important role to understand the characteristics of the “Magnetic field- Charged particle System”. The “right-hand rule” is as follows:

As the above image explains, if we arrange the thumb, middle finger and the index finger in an above-shown manner, we can easily decide the direction of the force experienced by the charged particle when moving in a particular direction in a magnetic field. But the above diagram is only applicable to the positively charged particle not for negatively charged particles like electrons. For negatively charged particles, the direction of the force experienced by the particle will be opposite to the direction shown in the above diagram. Now,If we observe the stated problem and arrange our fingers accordingly we will get the following pattern:

But our particle is negatively charged (electron) and so the force direction on the particle will be opposite to the direction shown in the above image.
The correct answer will be the option (C)i.e. downward.

Note
The conventional “right hand rule” shown in various diagrams is applicable to the positively charged particles. If we are dealing with the negatively charged particles then we need to reverse the direction of the force experienced by the particle.