Question

Two lamps rated (100 W, 220 V) and (60 W, 220 V) are connected in parallel. Which lamp consumes more energy and which one gives more brightness ? Find the
resistance of each lamp. (Take supply voltage as 220 V)

Answer 1

Since the lamps are connected in Parallel,


We can use the equation ,
P = I^2 × R ------- (1)


We know that,
P = VI -----------(2)

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Considering the  lamp of 100 w & 220 v


We can find out its current using (2)


100 = I × 220
.: I = 100/220
     = 0.45 A //
now using (1)
P = I^2 R
we can find out resistance
100 = (0.45)^2 × R
R = 100/ (0.45)^2
   = 493.82 ohm
= 494 ohm //
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Considering the lamp having 60 w & 220 v


We can find out its current using (2)
60 =  220 × I 
I = 60/220
  = 0.272 A //
now using (1)
P = I^2 R
we can find out resistance


60 = ( 0.272)^2 × R
R = 810. 9 ohm
= 811 ohm //

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By observing the resistances and currents,


First lamp have resistance of 494 ohm and current of 0.45 A.. 
  & 
Second lamp have resistance of 811 ohm and current of 0.27 A..


1st lamp have more brightness , bcoz it got less resistance and much more current flows through it.

Answer 2

hope it helps you........