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The resistance of the series combination of two resistances is S. When they are joined in parallel the total resistance is P. If S=nP, then the minimum possible value of n is

Asked in JEE Main 2004 · Series and parallel combinations

• (1) 4
• (2) 3
• (3) 2
• (4) 1

Step-by-step solution

Why the other options are wrong

• (2) No standard slip gives 3; (R₁+R₂)²/(R₁R₂) is never below 4.
• (3) Takes S=R and P=R/2 for two equal resistors, forgetting that in series two equal resistors give 2R.
• (4) Assumes the series and parallel values could be equal, which is impossible for positive resistances.

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