Q120 / 197 · NEET 2009 (Mains) · Physics

A wire of resistance $12 \mathrm{ohms}$ per metre is bent to form a complete circle of radius $10 \mathrm{~cm}$. The resistance between its two diametrically opposite points, A and B as shown in the figure, is : Figure

  • A
    $6 \Omega$
  • Correct answer
    B
    $0.6 \pi \Omega$
  • C
    $3 \Omega$
  • D
    $6 \pi \Omega$

Solution

Total resistance of wire $=12 \Omega \times 2 \pi \times 10^{-1}$ $$ =2.4 \pi $$ Resistance of each half $=\frac{2.4 \pi}{2}=1.2 \pi$ and as about diameter both parts are in parallel $$ \text { Req. }=\frac{1.2 \pi}{2}=0.6 \pi \Omega $$

Hence, the correct answer is option: 'B'.

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