Question

An electron beam projected along positive x-axis deflects along the positive y-axis. If this deflection is caused by a magnetic field, what is the direction of the field?

Answer 1

Hint: Whenever a current-carrying conductor brings in a magnetic field, there will be a force acting on the conductor. We can find out the magnetic field direction by using Fleming’s left-hand rule.

Complete step by step answer:

To find the direction of the magnetic field, we can use Fleming’s left-hand rule. According to this law, whenever a current-carrying conductor is placed in a magnetic field, it experiences a force in a perpendicular direction to the direction of the current and magnetic field. To understand easily, the middle finger, forefinger and thumb of the left hand have to be placed in perpendicular directions. Then the forefinger represents the direction of the magnetic field, the middle finger represents the direction of current flow and the thumb represents the direction of the force.
Here the charges are negative. So the current will be in the opposite direction to the electron flow. The electron beam is projected along the positive x-axis direction. Due to the presence of the magnetic field, these electron beams get deflected to the positive y-axis direction. So according to the left-hand rule, the magnetic field will be in the positive z-axis direction.
Additional information: Fleming’s left-hand rule is commonly used in the electric motor applications, while Fleming’s right-hand rule commonly used for the electric generators. According to the right-hand rule, the forefinger represents the direction of the magnetic field, the middle finger represents the direction of induced emf and the thumb represents the direction of motion of the conductor when we are keeping our forefinger, middle finger and thumb of the right hand in mutually perpendicular directions.

Note: In this question, the charges are electrons. So the current flow will be in the opposite direction of electron flow. If we are not considering this, the direction of the magnetic field will be in the opposite direction.