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  4. Two electric bulbs 40 W, 200 V and 100 W, 200 V are connected in series. Then the maximum voltage that can be applied across the combination, without fusing either bulb (in V) is

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Q. Two electric bulbs 40 W, 200 V and 100 W, 200 V are connected in series. Then the maximum voltage that can be applied across the combination, without fusing either bulb (in V) is

KCETKCET 1997Current Electricity

Solution:

Maximum voltage to a bulb is 200 V. In series, same current passes through each bulb.
Resistance of 40 W bulb = $\frac{200 \times 200}{40} = 1000 \Omega$
Resistance of 100 W bulb = $\frac{200 \times 200}{100} = 400 \Omega$
Current in 40 W bulb for 200 V = $\frac{200}{1000} $ = 0.2 A
Voltage across 100 W bulb for 0.2 A = 400 $\times$ 0.2 = 80 V
Total voltage = 200 + 80 = 280 V