In designing a velocity selector that uses uniform perpendicular electric and ma

Question

In designing a velocity selector that uses uniform perpendicular electric and magnetic fields, you want to select positive ions of charge 5.00 e that are traveling perpendicular to the fields at 8.75 km/s . The magnetic field available to you has a magnitude of 0.550 T .

A) What magnitude of electric field do you need?

B) Show how the two fields should be oriented relative to each other and to the velocity of the ions.

C) Will your velocity selector also allow the negative ions of charge -5.00 e to pass through undeflected?

D)Will your velocity selector also allow the positive ions of charge different from 5.00 e  to pass through undeflected?

Explanation / Answer

A)   Magnetic and electric fields both are perpendicular to each other so the angle between the two fields is 90 degrees. So the sine(angle) = 1.

Force = qvB

F        = 5 * 8.75 * 0.550.

F        = 24.06 N

Also F = qE

       E = 24.06/5

           = 4.8125 N/C.

B)    The magnetic field is perpendicular to both the ion velocity and the electric field.

       Ion with a speed v = E / B

      It passes in a straight way.       ..........................o

C) No it would work fine just the way it is.

D) For ions with a larger speed, the magnetic force exceeds the electric force and these ions are deflected up of the

    beam.

    The opposite happens for slower ions, so they are deflected down out of the beam.

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