1. Consider a conducting ring made of thin wire wheel: d is the diameter of the wire and D is the diameter of the ring (D>>d).
A charge Q placed on the ring is just enough to cause the ring to break apart due to electrostatic repulsion.
All linear dimensions are doubled (multiplied by 2); what is the new charge required to break this new ring?
It finds the charge required to break the ring due to electrostatic repulsion.