Question

The electron gun in an old TV picture tube accelerates electrons between two parallel plates 1.5 cm apart with a 30 kV potential difference between them. The electrons enter through a small hole in the negative plate, accelerate, then exit through a small hole in the positive plate. Assume that the holes are small enough not to affect the electric field or potential. a)What is the electric field strength between the plates?

Answer 1

For a pair of charged parallel plates (think capacitor) where the plate size is much bigger compared to the plate spacing, we can approximate the electric field as having a constant magnitude everywhere between the plates. The electric field strength is given by:

E = ΔV/d

E = electric field strength, ΔV = potential difference, d = plate spacing

Given values:

ΔV = 30×10³V, d = 1.5×10⁻²m

Plug in and solve for E:

E = 2 megavolts/meter