AP EAMCET · PHYSICS · Current Electricity
A lamp is rated at \(240 \mathrm{~V}, 60 \mathrm{~W}\). When in use the resistance of the filament of the lamp is 20 times that of cold filament. The resistance of the lamp when not in use is
- A \(54 \Omega\)
- B \(60 \Omega\)
- C \(50 \Omega\)
- D \(48 \Omega\)
Answer & Solution
Correct Answer
(D) \(48 \Omega\)
Step-by-step Solution
Detailed explanation
When the lamp is in use, \(\begin{aligned} & \mathrm{R}=\frac{\mathrm{V}^2}{\mathrm{P}}=\frac{240 \times 240}{60}=960 \Omega \\ & \therefore \quad \mathrm{R}=20 \mathrm{R}^{\prime} \Rightarrow \mathrm{R}^{\prime}=\frac{\mathrm{R}}{20}=\frac{960}{20}=48 \Omega \end{aligned}\)
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