The device pictured is called a velocity selector. Two charged plates are placed

Question

The device pictured is called a velocity selector. Two charged plates are placed in a uniform B-field, so that the direction of the E-field between them is at a right angle to the direction of the B-field. Charged particles are then sent through the plates. Only those for which the electrical and magnetic forces exactly cancel out are allowed to pass to the far end.

If we send hydrogen nuclei (that is, protons) into the selector with the strength of the E-field at 2000 N/C and the strength of the B-field at 0.8 T, what is their velocity if they make it through?

A:1000 m/s

B:1600 m/s

C:2000 m/s

D:2500 m/s

E:3100 m/s

-An explanation would be great!

Explanation / Answer

Force by electric field is cancelled by force due to magnetic field.

F due to electric field= Eq

F due to magnetic field = Bqv

Eq = Bqv

V = E/B = 2000/0.8

= 2500 m/s

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