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Two electric bulbs marked 20 W- 220 V and 100 W - 220 V are connected in series to 440 V supply. Which bulb will be fused? |
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Answer» SOLUTION :To CHECK which bulb will be fused, the voltage drop across each bulb has to be CALCULATED. The resistance of a bulb, `R=(V^(2))/(P)=(("Rated Voltage")^(2))/("Rated Power")` For 20W-220V bulb, `R_(1)=((220)^(2))/(20)Omega=2420Omega` For 100W-220V bulb, `R_(2)=((220)^(2))/(100)Omega=484Omega` Both the bulbs are connected in series. So the current which passes through both the bulbs are same. The current that passes through the circuit, `I=(V)/(R_("tot"))`. `R_("tot")=(R_(1)+R_(2))` `R_("tot")=(484+2420)Omega=2904Omega` `I=(440V)/(2904Omega)=0.151A` The voltage drop across the 20 W bulb is `V_(1)=IR_(1)=(440)/(2904)xx2420=366.6V` The voltage drop across the 100 W bulb is `V_(2)=IR_(2)=(440)/(2904)xx484=73.3V` The 20 W bulb will be fused because its voltage rating is only 220 V and 366.6 V is dropped across it. |
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