Which glows brightest

Half the people I ask say 60w, but then the rest say 100w?

Well, if they are in series, then they both experience the same current, but the 100W one has more filament to heat up (because more filament is required to produce more light), so that means it’ll be colder, but if thee is more filament then even if it’s colder then it still might produce more light. I suppose if it’s colder then that means that it is less efficient and the 60W one would therefore be more efficient, and the 60W one has more resistance so takes up more of the voltage so it consumes more power which means that if it’s using more power at a higher efficiency then it must be brighter. I conclude that the 60W bulb is indeed brighter. I’m not really sure what’s up with Khrushchev’s law, but I seem to be predicting that the 100W bulb will be dimmer.

I just looked up Khrushchev’s law and found nothing, so maybe it’s just bogus and can’t be trusted.

I just did a little math and assuming both bulbs have the same efficiency at all power levels (which they don’t) then they would both have the same power level. At lower power levels efficiency is lost and since the 100W one is more starved of power it is at a lower efficiency which means it’s going to be dimmer.

Thank you very much Jason9 for your help... :)

Try Kershaw's law.

Billy, you mean Kirchhoff's law?

The two bulbs are like two resistances where the 60W is larger than 100W. As Booth are crossed by the same current (as they are in series) the larger resistance will produce a larger power dissipation therefore thisone will be brighter