Q1. [1]
If four identical resistors, of resistance 8 ohm, are first connected in series so as to give an effective resistance Rₛ, and then connected in parallel so as to give an effective resistance Rₚ, then the ratio Rₛ/Rₚ is
- (a) 32
- (b) 2
- (c) 0.5
- (d) 16
Previously asked in CBSE board exam
2023 31/1/1 Q13
Generated by claude-sonnet-4-6 · 2026-06-15 06:46 · grounding rag
Model Answer
(d) 16
$R_s = 8+8+8+8 = 32\ \Omega$; $\dfrac{1}{R_p} = \dfrac{1}{8}\times4$, so $R_p = 2\ \Omega$; $\dfrac{R_s}{R_p} = \dfrac{32}{2} = 16$.
Source: Chapter 11, Sections 11.6.1 and 11.6.2
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Explanation
For series: add all resistances → $R_s = nR = 4\times8 = 32\ \Omega$.
For parallel: $R_p = R/n = 8/4 = 2\ \Omega$.
Ratio = 32/2 = 16. A common trap is to compute the ratio the wrong way round or to forget the formula for identical resistors in parallel ($R_p = R/n$). Always check which arrangement gives the larger resistance (series always does).
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