When two sources of waves with the same frequency are active, what must the path length difference be at some point in space for the waves to interfere destructively?.

A6.0-μf air-filled capacitor is connected across a 100-v voltage source. after the source fully charges the capacitor, the capacitor is immersed in transformer oil (of dielectric constant 4.5). how much additional charge flows from the voltage source, which remained connected during the process?