Crossed E and B fields "Velocity
This physlet illustrates Crossed
Electric and Magnetic fields (a "velocity selector").
Assume there are two parallel
horizontal plates (at the top and bottom of the window shown on the
right) - thus there is a vertical electric field. If Ey is positive,
the electric field points North (think of the top plate as being
negative and the bottom plate being positive), if Ey is negative, the
electric field points South (and the charges on the plates are
There is a magnetic field
perpendicular to the screen - if Bz is positive, it is out of the
screen (and you see a "circle and a dot" as though you are
looking at the tip of an arrow), if Bz is negative, it is into the
screen (and you see the "cross" as though you were looking
at the back end of the arrow .. the fletching!).
Two charges enter from each side,
with the magnitude of the velocity you give below. The
Positive charges are green, the
negative charges are Red.
You can change the initial speed
of the charges, the magnetic field strength and the electric field
strength, the magnitude of the charges (the signs are already chosen
as +/- on each side), and the mass of the charges.
a) Set Ey to zero to look at only B field
b) Set Bz to zero to look at only E field