What happens to electricity when voltage is high in an insulator?

When voltage is high in an insulator, electricity can "leak" across the insulator, which means that a small amount of electric current can flow through the material even though it is normally not a conductor. Insulators are designed to prevent the flow of electricity under normal conditions; however, when the voltage exceeds the material's dielectric breakdown strength, it can cause the insulating material to become conductive, allowing some current to pass through.

This phenomenon occurs when the electric field strength within the insulator becomes large enough to ionize the material, resulting in a partial breakdown of its insulating properties. As a result, a pathway for current can develop, leading to the leakage of electricity. This is why, at high voltages, even insulators are not completely effective at preventing electrical conduction, which can lead to unintended circumstances such as short circuits or electrical arcs.

The other choices do not accurately reflect what occurs in this situation: electricity does not flow freely through an insulator under normal conditions; it does not simply decrease in a manner that would imply its behavior is unaffected; and it does not stop altogether, as some degree of leakage can occur when voltage levels are sufficiently high.