Velocity Filter

Description:

Charge particle can have any value of velocity, if there is a requirement of a charge that has a particular velocity, then velocity filter can be used.

Velocity filter allows us to gain a charge particle with a particular velocity by eliminating all the other charge particles with different velocities.

To filter out velocities, the charge particles are passed through a space containing both electric field and magnetic field.

As we know when a charge particle enters an electric field it takes a parabolic path and when a charge particle enters a magnetic field it takes a circular path, hence when the charge enters a space where both the fields are present, the charge moves in the direction of resultant force.

If the charge moves straight without change in direction, then the resultant force is zero i.e. electric force is equal to magnetic force.

F_E = F_B

∴ qE = qVB

Velocity of charge particle that is allowed to escape the filter is dependent on electric field and magnetic field that can be controlled and set to a desired value to filter out velocities.

If velocity of a charge is greater than the desired velocity, then it will hit the lower wall i.e. effect of magnetic force will be larger and if velocity of a charge is lower than the desired velocity then, it will hit the upper wall i.e. effect of electric force will be prominent.