There are 2 bulbs namely 6o watts and 40 watts.Which bulb will glow brighter?

Question

If both are connected in series to 240V supply and if they are connected in parallel to 240v supply.Please specify the reason with necessary calculations.

Answer 1

60 watts will be brighter but you better make sure beforehand that you can put a 60 watt bulb in without burning the source out.

Answer 2

40 watts

Answer 3

60 watts

Answer 4

If the two lamps are connected in series, 40 watt bulb will glow brighter.This is because the resistance of the bulb filament will be in the ratio of 2:3. that means if the resistance of 60 W   lamp is 2R then that of 40 W lamp will be 3R.

   when resistances  of 2R and 3R are connected in series and a voltage of  240 volt is applied , the voltage across 40 W bulb will be Current x 3R. If I is the current passing thro both the bulbs the voltage across 40 W will be  I x 3R and across 60 W bulb would be I x 2R. This means the voltage of 240 volts will be divided in the ratio of 3:2.Thus voltage across 40 watt bulb would be 144 volts and and across 60 W bulb it would be 96 volts. Thus the 40 watt bulb will glow brighter in comparison to 60 watt bulb.Is it clear or needs more elaboration.

Answer 5

This is an easy one..

'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...

cheers..:)