Level 1: A Bulb With a Capacitor: Dark on DC, Glowing on AC. How?
Double the frequency, then swap in a coil.
A bulb in series with a capacitor glows on a 220 V, 50 Hz supply. The frequency is raised to 100 Hz at the same voltage. The capacitor is then replaced by an inductor and the same change is made. The bulb:
A capacitor's reactance falls as the frequency rises, while an inductor's reactance rises with frequency. The bulb's brightness follows the current, which goes up when the reactance goes down.
So at 100 Hz the bulb with the capacitor gets more current and glows brighter, while the bulb with the inductor gets less current and glows dimmer. The two components respond to frequency in opposite ways.
Every Level 2 starts from a quick question, Level 1, and changes one thing. Seeing what that change does is the skill JEE Main tests. Try it here, free and with no signup, then read the worked answer.
