A uniform metal wire of length / has $10 \Omega$ resistance. Now this wire is stretched to a length $2 /$ and then bent to form a perfect circle. The equivalent resistance across any arbitrary diameter of that circle is

• Correct answer
  A

  $10 \Omega$
• B

  $5 \Omega$
• C

  $40 \Omega$
• D

  $20 \Omega$

Solution

$R_0=10 \Omega$ After stretching its length upto 2l $R_1=n^2 R_0$ $=4 R_0$ $=40 \Omega$
$R_{A B}=\frac{20 \times 20}{20+20}=10 \Omega$

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