Question

In detail, explain what role magnetism play in the 'Charge to Mass ratio of an electron' experiment performed by J.J. Thomson?

How can magnetism alter the expected results?

Why is it important for the electron beam to be perpendicular to all non-negligible magnetic fields?

Answer 1

1) Magnetism plays an important role in charge to mass ratio experiment. In this, the electron enters a region between electric field plates. At this point of time, magnetic field is applied to the electron. Now, we have both the electric force and magnetic force acting on the electron. The magnetic field applied will exert a force on the electron and will deflect the electron from its original path .

2) If the magnetic force is balanced with other forces, there will be no deflection at all. The electron will continue to move in x-direction. When we remove the magnetic field, there is only electric force.

3) We know that the magnetic force formula is given as

F = qvBsin

where is the angle between direction of electron beam and magnetic field.

so if electron beam is perpendicular to magnetic field we have

F = qvB sin 90

F = qvB

Therefore, we get maximum magnetic force when beam is perpendicular to the field.