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Three equal resistances when combined in series are equivalent to 90 o

June 1, 2025 by rawan239

Three equal resistances when combined in series are equivalent to 90 ohm. Their equivalent resistance when combined in parallel will be:

10 ohm

30 ohm

270 ohm

810 ohm

This question was previously asked in

UPSC NDA-2 – 2015

Download PDF Attempt Online

Let R be the resistance of each of the three equal resistors. When connected in series, the equivalent resistance (Rs) is the sum of individual resistances: Rs = R + R + R = 3R. Given Rs = 90 ohm, we have 3R = 90 ohm, so R = 30 ohm. When the three equal resistors are connected in parallel, the equivalent resistance (Rp) is given by the formula 1/Rp = 1/R + 1/R + 1/R = 3/R. Thus, Rp = R/3. Substituting R = 30 ohm, we get Rp = 30 ohm / 3 = 10 ohm.

Calculation of equivalent resistance for resistors connected in series and parallel.

For N equal resistors of resistance R, the equivalent resistance in series is NR, and the equivalent resistance in parallel is R/N.

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