Level 1: 300 V Across a Coil on a 220 V Supply: Faulty Meter?
Thirty, eighty and forty volts. Find the supply.
In a series LCR circuit on an AC supply, voltmeters read 30 V across the resistor, 80 V across the inductor and 40 V across the capacitor. The supply voltage (rms) is:
The inductor and capacitor voltages are opposite in phase, so together they give 80 − 40 = 40 V. That net reactive voltage is at right angles to the resistor's voltage.
The supply is 50 V, although the three meter readings add up to 150 V. Adding the readings as plain numbers (150 V), or adding only the resistor and capacitor (70 V), are the usual mistakes.
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.
