Question 4
An electron enters perpendicularly into a uniform magnetic field which has a flux density of 0.12T. This results in a magnetic force of 9.6 x 10-19 N on the electron. Calculate the speed of the electron as it enters the magnetic field.
(e = 1.6 x 10-19 C)
.
Observation
This was also another popular question because the performance was impressive. Majority of the candidates recognized the relationship between magnetic force, F, speed of the electron v, flux density B and direction of entry Ɵ but some candidates failed to include sin Ɵ which renders the formula incomplete.
The expected answer
F = evB sin
