Q.

Two bulbs one rated 100 W at 220 V and the other 200 W at 220 V, are connected in series to the electric supply at 220 V the current drawn by the two bulbs is [[1]] A.


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Detailed Solution

When two bulbs of ratings 100 W, 220 V and 200 W, 220 V are connected in series to the electric supply at 220 V then the current drawn by the two bulbs is 0.3 A.
It is given that two bulbs of ratings 60 W, 220 V and 40 W, 220 V are connected in parallel combination with the mains at 220 V.
Let the bulb with Power,
P=100 W and potential difference,
  V=220 V be Bulb 1.
Let the bulb with Power,
(P)=200 W and potential difference,
   V=220 V be Bulb 2.
It is known that the power P of the component is given by the relation
 P=V²R  or
 R=V²P
Where V and R are the potential difference and the resistance respectively.
Therefore, the resistance of bulb 1 is given as
    R1=2202100
R1=484 Ω
Similarly, the resistance of bulb 2 is
     R2=2202200
R2=242 Ω
Since, they are connected in series, the equivalent resistance is equal to
     R=R1+R2
 R=484+242
 R=726 Ω
Now, from the Ohm’s law, the current drawn is
     I=VR
On substituting the given value, we get the current as
I=220726
I=0.30 A
The total current drawn by the two bulbs is 0.30 A.
 
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