Question

You are working in a manufacturing plant. In one particular machine, electric charges are suspended above a uniformly charged disk of radius R. The disks become corroded rapidly and must be replaced daily. Your supervisor comes to you one day and tells you that he wants to replace the disks with much cheaper washers of radius R with a concentric hole of radius R/3. He asks you to determine by what factor the charge on the disk must be increased so that a uniform charge on the washer would provide the same electric field at a distance x = R on the central axis as did the disk.

q washer/ q disk= ?

Answer 1