Two lamps, one rated 100 W at 220 V and the other 200 W at 220V are connected (i) in series and (1)
in parallel to electric main supply of 220V. Find the current drawn in each case.
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PHYSICS
Two lamps, one rated 100 W at 220 V, and the other 60 W at 220 V, are connected in parallel to electric mains supply. What current is drawn from the line if the supply voltage is 220 V?
October 15, 2019avatar
Shriya Santhanam
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ANSWER
From Joule's Law of heating,
P=V
2
/R
For first lamp,
R
1
=220
2
/100
For second lamp,
R
2
=220
2
/60
When they are connected in parallel,
R
eq
1
=
R
1
1
+
R
2
1
=
220
2
/100
1
+
220
2
/60
1
⟹R
eq
=220
2
/160
From Ohm's Law,
V=IR
eq
220=
160
220
2
I
I=0.73 A
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