a bulb of 100W and anather bulb of 200W , rated supply
voltage 230v.when supply voltage is reduced to 100v,which
bulb will give more light? and why with calculation?

Answers were Sorted based on User's Feedback

Answer / nimish

P = V*i

For 100w bulb i = 100/230 = 0.4 A

For 200w bulb i = 200/230 = 0.8 A

Now voltage is reduced to 100 V , i = 100 / 100 = 1 A

i = 200 / 100 = 2 A

So, 200 W bulb will give more light.

Is This Answer Correct ?    63 Yes 10 No

Answer / glen



FOR 200W
FOR 100W


Is This Answer Correct ?    18 Yes 8 No

Answer / nitin

now in both cases whtevr the voltage ,it is same for both
now the main culprit is r,the bulb which has more
resistance would glow dimmer as per above formula.
we have used the above formula bcaz ,elctrcl instruments
are designd for constant voltage.
as power is inversely proportonal to the resistance (above
formula)therefor 200w bulb would have less resistance and
glow more

Is This Answer Correct ?    13 Yes 6 No

Answer / pillay

If the illuminating efficiency of the filament is directly propotional to the current flow than I belive the answers that say the 200 watt bulb will glow brighter than the 100 watt bulb at 100 volts

Is This Answer Correct ?    8 Yes 4 No

Answer / skimatix

At 230V a 100W bulb will draw ~ 434mA
At 230V a 200W bulb will draw ~ 869mA

By reducing the voltage the current will rise, P = VI.

At 100V a 100W bulb will draw = 1A
At 100V a 200W bulb will draw = 2A

Is This Answer Correct ?    6 Yes 3 No

Answer / sibtain

the brightness of the bulb is depend on its resistance.its
totally wrong to say that bulb will fuse.in our life when
electricity is dim are you ever seen that bulb will burn? no

Is This Answer Correct ?    3 Yes 2 No

Answer / mohit goyal

if both are connected in series. so 100w lamp more bright because its resistance is high so voltage drop is high in case of series. current is same both lamp.

if both r connected in parallel. so 200w lamp more bright because in case of parallel. voltage across each lamp is same so 200w lamp more bright.

Is This Answer Correct ?    3 Yes 2 No

Answer / dilip

If we operate a 230V rated bulb on 100V the current will be
almost 2.5 time more than the 230V. So both bulbs will be
fused and none of it will glow.
P = V*i

For 100w bulb i = 100/230 = 0.4 A

For 200w bulb i = 200/230 = 0.8 A

Now voltage is reduced to 100 V , i = 100 / 100 = 1 A

i = 200 / 100 = 2 A

If we operate a 230V rated bulb on 100V the current will be
two time more than the 230V. So both bulbs will be fused
and none of it will glow.

Is This Answer Correct ?    10 Yes 11 No

Answer / vasanth

100w bulb will give more light
due to p=v*i, i=v/r.
calculate R value
lighting will related to heat loss
calculate heat generated /100 volt

Is This Answer Correct ?    13 Yes 15 No

Answer / pradeep.b

General guid : If voltage reduces then current increases.

A 230 volts rated Bulb can't be operated on 100volts
becuase, when you starts operating a 230 volts rated bulb
in 100 volts, the current increases between 2 to 2.5 times.

Is This Answer Correct ?    2 Yes 5 No

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