Q221 / 225 · JEE Main 2005 · Physics

The resistance of hot tungsten filament is about 10 times the cold resistance. What will be the resistance of $100 \mathrm{~W}$ and $200 \mathrm{~V}$ lamp when not in use?

  • Correct answer
    A
    $40 \Omega$
  • B
    $20 \Omega$
  • C
    $400 \Omega$
  • D
    $200 \Omega$

Solution

$R_{\text {hot }}=\frac{V^2}{P}=\frac{200 \times 200}{100}=400 \Omega$ cold resistance $=R_{\text {hot }} / 10=400 / 10=40 \Omega$

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

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