Answer / wareagle

Ksb Quote "40 wattbulb has higher resistance(1440) so a
low current pass through it but 60 watt has low resistance
it glows brightly" That would be true if the bulbs are
connected in parallel but they are connected in series.
Read the question. Do you know what that means?

Ksbn That is incorrect. Lets find the answer.
Voltage = 240 volts
Watts = 40 watt and 60 watts
R60 = 240x240/60= 960 ohms
R40 = 240x240/40= 1440 ohms
Total of R60 + R40 = 960 + 1440 = 2400 ohms for series ckt
Amps = 240/2400 = 0.10 amps flowing thru both 40w and 60w
watts = amp²x R
watts for 60 watt = amp²x R = 0.10² x 960 = 0.01 x 960 =
9.6 watts
watts for 40 watt = amp²x R = 0.10² x 1440 = 14.4 watts
Therefore 40 watt is brighter.
Remember the bulbs are connected in series not parallel.

Answer / wareagle

40

Answer / wareagle

posted by Syed "so calculating resistances,
R60=240*240/60=960ohm,
R40=240*240/40=1440ohm,
Req=(960*1440)/(960+1440)=576ohm,
Total current through the circuit:"

The lights are in series not parallel. You are calculating
the parallel equivalent. of course the 60 watt will be
brighter in parallel. But the question says series.
Try it over in series and the 40 w will be brighter.

Answer / ksb

40 wattbulb has higher resistance(1440) so a low current
pass through it but 60 watt has low resistance it glows
brightly

Answer / syed golam kibria

'V' across both the bulbs will be the same...
we have,
P=V^2/R;
R=V^2/P;
so calculating resistances,
R60=240*240/60=960ohm,
R40=240*240/40=1440ohm,
Req=(960*1440)/(960+1440)=576ohm,
Total current through the circuit:
240/576=0.625A
current through the 40W bulb,
0.25A
current through the 60W bulb,
0.375A
Now,
E=i^2*r*t
E40=0.25*0.25*1440*t=90t
E60=0.375*0.375*960*t=135t
for a same time period 't'...60W bulb dissipates more energy...
so the 60W bulb glows brightly...

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