In a television picture tube, electrons are accelerated by thousands of volts through a vacuum. If a television set were laid on its back, would electrons be able to move upward against the force of gravity? What potential diffrence , acting over a distance of 3.0 cm, would be needed to balance the downward force of gravity so that an electron would remain stationary? Assume that the electric field is uniform.

Answer 1

The electric force on an electron is e V/d, where e is the electron charge and d is the separation. (V/d is the E field strength). To balance the gravitational force on Earth,
e V/d = m g
where g is the acceleration of gravity and m is the electron mass.
Solve for V = m g d/e

You should find the weight-balancing voltage to be very small compared to the actual TV picture tube voltage