Moving Charges and Magnetism · Question 89

In Thomson mass spectrograph, if E B, then the velocity of electron beam will be

1. | E|| B|
2. E B
3. | B|| E|
4. E2 B2

Answer

(1) | E|| B|

Solution

In crossed electric and magnetic fields the beam passes undeflected when the two forces balance:

eE = evB

⇒ v = EB

∴ Velocity of the electron beam = | E|| B|

Answer: (1)