3012. Two lamps, one rated 100 W at 220 V and the other 200 W at 220V

1.	3012. Two lamps, one rated 100 W at 220 V and the other 200 W at 220V are connected-(i) in series and(ii) in parallel to electric main supply of 220V. Find the current drawn in each case.
Answer» Resistance of 1st lamp, R1 = V1²/P1 = (220)²/100= 484 ohm resistance of 2nd lamp, R2 = V2²/P2 = (220)²/200= 242 ohm. if lamps are connected in series , Req = R1 + R2 = 484 + 242 = 726 ohmso, I = V/Req = 220/726 = 20/66 Amp = 10/33 = 0.3 amp if lamps are connected in parallel combination, Req = R1R2/(R1 + R2)= 484 × 242/(484 + 242)= 484 × 242/726= 44 × 242/66 = 4 × 242/6 = 484/3 ohm so, I = V/Req = 220/(484/3) = 660/484 = 60/44 = 15/11 = 1.36 Amp in series it is rated 0.3 ampere and in parallel it is rated 1.36 ampere

3012. Two lamps, one rated 100 W at 220 V and the other 200 W at 220V are connected-(i) in series and(ii) in parallel to electric main supply of 220V. Find the current drawn in each case.

Answer»

Resistance of 1st lamp, R1 = V1²/P1 = (220)²/100= 484 ohm resistance of 2nd lamp, R2 = V2²/P2 = (220)²/200= 242 ohm.

if lamps are connected in series , Req = R1 + R2 = 484 + 242 = 726 ohmso, I = V/Req = 220/726 = 20/66 Amp = 10/33 = 0.3 amp

if lamps are connected in parallel combination, Req = R1R2/(R1 + R2)= 484 × 242/(484 + 242)= 484 × 242/726= 44 × 242/66 = 4 × 242/6 = 484/3 ohm

so, I = V/Req = 220/(484/3) = 660/484 = 60/44 = 15/11 = 1.36 Amp

in series it is rated 0.3 ampere and in parallel it is rated 1.36 ampere

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