Current Electricity 3 Question 7

4. Two electric bulbs rated at 25W,220V and 100W,220V are connected in series across a 220V voltage source. If the 25W and 100W bulbs draw powers P1 and P2 respectively, then

(2019 Main, 12 Jan I)

(a) P1=16W,P2=4W

(b) P1=4W,P2=16W

(c) P1=9W,P2=16W

(d) P1=16W,P2=9W

Show Answer

Solution:

  1. Resistance of a bulb of power P and with a voltage source V is given by

R=V2P

Resistance of the given two bulbs are

and

R1=V2P1=(220)225R2=V2P2=(220)2100

Since, bulbs are connected in series. This means same amount of current flows through them.

Current in circuit is

i=VRtotal =220(220)225+(220)2100=111A

Power drawn by bulbs are respectively,

P1=i2R1=1112×220×22025=16W and P2=i2R2=1112×220×220100=4W



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