A 20 Watt bulb glows brighter than a 100 W bulb. Why?

Question

They are connected in series across a 230 Volt AC supply (and 230 V is their name plate volt-rating).

Answer 1

The light output of a light bulb is measured in lumens. The electricity usage is measured in watts. The efficiency of a light bulb is measured in lumens of light produced divided by the watts of electricity used.

For example, a typical 20-watt light bulb produces only 210 lumens of light. A 100-watt light bulb produces 1600 lumens of light. It requires about ten 20-watt bulbs (200 total watts of electricity used) to produce as much light as one 100-watt bulb. Therefore, a 100-watt bulb is twice as efficient as a 20-watt bulb.

The voltage drop across the two 20 w bulbs connected in series is less than two 100 w bulbs connected in series as there is much resistance in 100 w bulbs hence they emit low light.

Answer 2

A lot of wrong answers, but Scott has it right.

IN SERIES is the key word the others missed.

In series, the bulb with the highest resistance will have the most power across it, and thus be the brightest.

numbers:

100 watt bulb, R:

P = E²/R

R = E²/P = 230²/100 = 529 ohms

20w bulb, R = 2650 ohms

total current = 230/ (2650+529) = 72mA

P = I²R

100w, P = 2.8 watts

20w, P = 13.8 watts

so the 20 watt bulb dissipates 5 times more power than the 100 watt one, so it's much brighter.

Note that the calculations are not very accurate because resistance of light bulbs varies a lot with voltage, but they can be used to give you an idea of what happens in series.

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Answer 3

Check again, you got the wrong values. 100 W bulbs blaze! whilst 20W only glow

Answer 4

Either you have them in the wrong boxes, or the 20 watt is a low energy bulb, and the 100 W is a regular one. Low energy bulbs give off a light FAR brighter than the energy they use. x

Answer 5

Hello, pls note that, 20W Bulb will never be brighter than 100W Bulb. This is possible, when the area of coverage for 20W bylb if small, when compared to the area of coverage of 100W Bulb. Both of them having the same supply voltage onle. Depending upon the consumption of current only they are specified as 20W & 100W. The glow is with respect to the product range only.

Answer 6

Because they are in series, the same current must flow through both. Now for each bulb, P = I^2 R. But the 20W bulb has a higher resistance than the 100 W bulb, so it dissipates more power when they are in series, and is brighter.

Answer 7

some materials transform energy better into other states if energy.

The 20 watt one i bet is much cooler in temperature then the 100Watt one

that because the materials in the 20Watt on change 230 Volt AC power into light more then heat where as the 100watt on produces more heat then light