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The difference between maximum and minimum resistance that can be obtained by connecting three resistances of \(\frac{1}{3}\ \Omega\) each is :

  • A.\(\frac{2}{3}\ \Omega\)
  • B.\(\frac{8}{9}\ \Omega\)
  • C.\(1\ \Omega\)
  • D.\(\frac{1}{9}\ \Omega\)

Answer: B

The difference is \(\frac{8}{9}\ \Omega\).

The maximum resistance comes from connecting all three in series and the minimum from connecting all three in parallel:

\[ \begin{aligned} R_{max} &= 3 \times \tfrac{1}{3} = 1\ \Omega \\ \frac{1}{R_{min}} &= 3 + 3 + 3 = 9 \Rightarrow R_{min} = \tfrac{1}{9}\ \Omega \\ R_{max} - R_{min} &= 1 - \tfrac{1}{9} = \tfrac{8}{9}\ \Omega \end{aligned} \]

1 Ω and 1/9 Ω are the maximum and minimum themselves, not their difference, and 2/3 Ω does not follow from either arrangement.

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