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Q24
(NDA-II/2015)
Science & Technology › Basic Science (Physics, Chemistry, Biology) › Electricity and magnetism
Answer Verified
Three equal resistances when combined in series are equivalent to 90 ohm. Their equivalent resistance when combined in parallel will be:
Result
Your answer:
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Correct:
A
Explanation
When three equal resistors are connected in series, the equivalent resistance is the sum of their individual resistances [2]. Given the series total is 90 ohm, each individual resistor (R) is calculated as 3R = 90, resulting in R = 30 ohm. For a parallel combination of these three identical resistors, the reciprocal of the equivalent resistance is the sum of the reciprocals of the individual resistances [1]. This is expressed as 1/Rp = 1/R + 1/R + 1/R, which simplifies to Rp = R/3. Substituting the individual resistance value (30 ohm) into this formula gives Rp = 30/3 = 10 ohm. Thus, the equivalent resistance of the three 30 ohm resistors when combined in parallel is 10 ohm.
Sources
- [2] Science , class X (NCERT 2025 ed.) > Chapter 11: Electricity > Activity 11.5 > p. 184
- [1] Science , class X (NCERT 2025 ed.) > Chapter 11: Electricity > Activity 11.6 > p. 186
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