In an industrial electrostatic paint-spraying system, a spherical spray nozzle becomes negatively charged.
State how the strength of the electric field around the spherical nozzle changes as the distance from the nozzle increases.
During a calibration test, an earthed metal test plate is brought near the negatively charged nozzle until an electrical discharge (spark) occurs. The discharge transfers 0.85 J0.85\text{ J}0.85 J of energy, and 2.5 μC2.5\ \mu\text{C}2.5 μC of charge is transferred. Calculate the potential difference between the spherical nozzle and the earthed plate.