A 110 V, 60 W lamp is operated from a 220 V AC mains supply using a capacitor in series (instead of a resistor). What is the approximate voltage across the capacitor?

110 V
190 V
220 V
311 V

Correct answer: 190 V

Solution

V_R = 110 V (rated lamp voltage). V_supply = 220 V. V_cap = sqrt(220² - 110²) = sqrt(36300) = 110*sqrt(3) ~ 190.5 V ~ 190 V.

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