Question:
Two bulbs 40 W and 60 W and rated voltage 240 V are connected in series across a potential difference of 420 V. Which bulb will work at above its rated voltage?
Two bulbs 40 W and 60 W and rated voltage 240 V are connected in series across a potential difference of 420 V. Which bulb will work at above its rated voltage?
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Two bulbs 40 W and 60 W and rated voltage 240 V are connected in series across a potential difference of 420 V. Which bulb will work at above its rated voltage?
Updated On: Apr 15, 2026
- 40 W bulb
- 60 W bulb
- Both will work
- None of these
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The Correct Option is A
Solution and Explanation
Step 1: Resistance
$R_{40} = \frac{240^{2}}{40} = 1440 \Omega$. $R_{60} = \frac{240^{2}}{60} = 960 \Omega$.
Step 2: Analysis
In series, the same current flows through both. The bulb with higher resistance (40 W) will have a higher voltage drop ($V=IR$).
Step 3: Calculation
Total current $i = \frac{420}{1440+960} = 0.175 \text{ A}$. Voltage across 40 W bulb $= 0.175 \times 1440 = 252 \text{ V}$, which is $> 240 \text{ V}$.
Final Answer: (A)
$R_{40} = \frac{240^{2}}{40} = 1440 \Omega$. $R_{60} = \frac{240^{2}}{60} = 960 \Omega$.
Step 2: Analysis
In series, the same current flows through both. The bulb with higher resistance (40 W) will have a higher voltage drop ($V=IR$).
Step 3: Calculation
Total current $i = \frac{420}{1440+960} = 0.175 \text{ A}$. Voltage across 40 W bulb $= 0.175 \times 1440 = 252 \text{ V}$, which is $> 240 \text{ V}$.
Final Answer: (A)
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