Question

What is the velocity of a beam of elections that produces no deflects when simultaneously subjected to an electric field of 3.8*10 and a magnetic field of 2.5 * 10 both field being mutually perpendicular and each normal to the beam

Answer 1

Its the electron beam is not deflected then,

F

m

=Ee

Bev=Ee

v=

B

E

According to the law of conservation of energy

2

1

mv

2

=eV

v=

m

2eV

m

2eV

=

B

E

m

e

=

2VB

2

E

2