a) The drum of a photocopying machine has a length of 42 cm and a diameter 12 cm. The electric field now above the drum's surface is 2.3x105 N/C. What is the total charge on the drum?
b) The manufacturer wishes to produce a desktop version of the machine. This needs reducing the drum length to 28 cm and the diameter to 8 cm. The electric field at the drum surface should not change. What must the charge on this new drum?