In a television set, electrons are accelerated from rest through a potential difference of 25 kV. The electron

Question

In a television set, electrons are accelerated from rest through a potential difference of 25 kV. The electrons then pass through a 0.30 T magnetic field that deflects them to the appropriate spot on the screen. Find the magnitude of the maximum magnetic force that an electron can experience.

Answer 1

Find the velocity of the electron from equating potential energy to kinetic energy:

Potential energy = V*qe V = 25kV, qe = electronic charge
Kinetic energy = 0.5*me*v^2, me = electronic mass

V*qe = 0.5*me*v^2

v = √[2*V*qe/me]

qe/me = 1.76*10^11, so v = 9.38*10^7 m/s

With this velocity find the magnetic force F = qe*(v x B). This is the vector cross product, indicating the force is at right angle to v and B. The magnitude is just qe*v*B

qe = -1.6*10^-19 coul

F = 1.6*10^-19 * (9.38*10^7 * 0.3) = 4.5*10^-12 N