This video demonstrates a light switch. By increasing/decreasing the resistance, the light affects the current, or the amount of charge over time. Ohm's law, I=V/R demonstrates this because if R is higher, than I is lower.
Less current means less power, as shown by the equation P=IV. So because V is a constant 120V (from the outlet), current is the only thing that affects the power. By increasing current, I can increase the power and brightness of the light, or by decreasing the current, I make the bright dimmer.
