An electron moves through a region of crossed electric and magnetic fields.The electric field E = 3200 V/m and is directed straight down.The magnetic field B = 0.80 T and is directed to the left.For what velocity v of the electron into the paper will the electric force exactly cancel the magnetic force?
A) 2500 m/s
B) 5000 m/s
C) 4000 m/s
D) 8000 m/s

Question

An electron moves through a region of crossed electric and magnetic fields.The electric field E = 3200 V/m and is directed straight down.The magnetic field B = 0.80 T and is directed to the left.For what velocity v of the electron into the paper will the electric force exactly cancel the magnetic force? 
A) 2500 m/s 
B) 5000 m/s 
C) 4000 m/s 
D) 8000 m/s

Quizplus · Accepted Answer

The force on a charged particle moving in an electric and magnetic field is given by:

F = q(E + v x B)

where q is the charge of the particle, E is the electric field, v is the velocity of the particle, and B is the magnetic field.

In this case, we want the electric force to exactly cancel the magnetic force, so:

qE = qvB

Canceling out the charge q, we get:

E = vB

Solving for v, we get:

v = E/B = 3200 V/m / 0.80 T = 4000 m/s

Therefore, the best choice is C) 4000 m/s.

An Electron Moves Through a Region of Crossed Electric and Magnetic