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

 

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Asked by piyushmalik024 | 7th Jul, 2019, 01:35: AM

Expert Answer:

Resistance R of each lamp from given power P and operating voltage V is obtained from the relation,
 
P = ( V2 / R )  ....................... (1)
 
Hence resistance of 100W, 220 V lamp = (220×220)/100 = 484 Ω
 
Resistance of 200W, 220 V lamp = (220×220)/200 = 242 Ω
 
when lamps are connected in series , equivalenet resistance = 484+242 = 726 Ω
 
Hence current drawn by lamps that are connected in series = 220/726 = 0.3 A
 
When lamps are connected in parallel, each lamp draws current independenly as per its wattage.
 
Current drawn by 100 W lamp = 100/220 = 0.45 A
Current drawn by 200 W lamp = 200/220 = 0.91 A
 
Hence total current drawn by lamps when they are connected in parallel = 0.45+0.91 = 1.36 A

Answered by Thiyagarajan K | 7th Jul, 2019, 10:33: AM

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