Question

For a uniformly charged disk of radius 95 mm , you wish to determine the electric field magnitude along the axis that runs through the disk center and perpendicular to the disk face. You want to get by with a minimal amount of work, so you need to know when you can get by with approximating the disk as an infinite sheet.

Part A

At what distance along the perpendicular axis does your error in E reach 10% of the actual value when you use this approximation?

Express your answer with the appropriate units.

z =10.6*10^-3 m

Incorrect

Answer 1

The electric field due to a disk of radius R is

The electric field due to an infinite sheet is

So the error is proportional to

When this error is 10% of the actual value

Solving this gives the distance along the perpendicular axis where the error in E reaches 10% of the actual value