Imagine an electron is traveling toward a parallel plate capacitor with speed v,
ID: 2039641 • Letter: I
Question
Imagine an electron is traveling toward a parallel plate capacitor with speed v, as shown in the figure.
a) As drawn, what will happen to the electron when it enters the capacitor (i.e. what will it experience, and how will it react)?
b) Now imagine that, in addition to the electric field, you apply a uniform magnetic field inside the capacitor to make the electron move straight through the capacitor undeflected. What should be the direction of the magnetic field? Explain your answer.
c) Write an expression for the strength of the magnetic field required for this to happen. (Hint: what should be the net force on the electron if it's moving in a straight line?)
Explanation / Answer
a) elctron will be deflected upward due electric force.
b) Into the page
here v is towards +x axis
when B is towards -z axis
magnetic force acting on the elctron,
F = q*(v cross B)
= -e*( vi cross -Bk)
= -e*(v*(-B) (-j))
= -e*v*B
so, magnetic force acts towards -y axis wgich balances the electric force.
c) for no deflection, |Fe| = |FB|
q*E = q*v*B
=> B = E/v <<<<<<-----Answer