Problem: A parallel-plate capacitor is designed so that the plates can be pulled apart. The capacitor is initially charged to a potential difference of 90 Volts when the plates are 1.0 mm apart. The plates are insulated so that the charge cannot leak off.
Part A: What is the potential difference between the plates when they are pulled to a new separation 3.0 mm apart?
Express your knowledge to solve the above problem.