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

JEE PHYSICS MCQ: CURRENT ELECTRICITY

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The resistance of hot tungsten filament is about

\mathrm{10}\,\,\mathrm{times}

the cold resistance. What will be the resistance of

\mathrm{100}\,\,\mathrm{W}

and

\mathrm{200}\,\,\mathrm{V}

lamp, when not in use?

View answer and explanation

Correct option: A

\mathrm{40}\,\,\mathrm{\Omega }

Option A (

\mathrm{40}\,\,\mathrm{\Omega }

) is correct because the resistance of the lamp when not in use is the cold resistance, which is 1/10th of the hot resistance.

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\mathrm{\rho }

3\,\,{\mathrm{m}^3}

3\,\,\mathrm{\Omega }

4.7\,\, \times \,\,{10^6}\,\,\mathrm{\Omega }\,\, \pm \,\,5\,\,\%

22.5\,cm