A circuit consists of a lightbulb, capacitor, battery, and open switch all in series. After the switch is closed, describe what happens to the brightness of the lightbulb. Assume the capacitor is initially uncharged. The lightbulb has resistance so this is essentially an RC circuit.

Since this is an RC circuit, an RC circuit can be used to provide various time delays. The capacitor is connected in parallel across the lightbulb. WITH the battery connected, when the switch is closed, the capacitor voltage increases towards the battery voltage at a rate determined by the lightbulb resistance and the capacitance of the capacitor (called the time constant (τ)). The bulb will not emit any light and will act like an open circuit until the voltage across the capacitor reaches a certain level that can bright the bulb, when this voltage is reached the lightbulb brights gradually and the capacitor discharges through it, the lightbulb turns off again because the capacitor voltage drops fast and the capacitor recharges again and the lightbulb brights again