VISUAL PHYSICS ONLINE

8.1 FROM THE UNIVERSE TO THE ATOM

THE ATOM

P81 010

Two parallel horizontal plates which are 8.0 mm apart in a vacuum have a potential difference of 120 V across them. The upper plate is positive with respect to the lower plate. The plates are in a constant magnetic field of 0.020 T and its orientation is shown in the diagram. A horizontal beam of electrons is directed between the plates as shown in the diagram.

(A)

Calculate the magnitude of the electric field between the plates.

(B)

Determine the magnitude and direction of the electric force of the electric field acting upon the electron beam.

(C)

Determine the direction of the magnetic force acting upon the electron beam.

(D)

Calculate the speed of the electrons that will allow the beam to pass undeflected between the plates (ignore the gravitational force).

charge of electron

View solution below only after you have completed the answering the question.

Solution

(A)

(B)

direction of electric force on electron beam

(C)

The direction of the magnetic force acting on the electron beam is found using the right-hand palm rule

(D)

For the beam to pass undeflected through the plates, the magnitudes of the electric force and magnetic force must be equal and act in opposite directions.