Question

is lightening of bulb a physical change

Answer 1

its a chemical change

Answer 2

As the light produced by theINCANDESCENT LAMP is due to heating effect of the conductor hence it is not a chemical change but a physical change.

But the main question came is that if temperature change happens then it should be a chemical reaction but it is not that because the chemical reaction defines that if there is occurrence of temperature change then it should led to formation of new compound and here it is not that case (Here the change is temperature is similar to boiling of water).Hence it is not a chemical change.

Now how heating happens .Basically the filament of the INCANDESCENT LAMP are made up of high resistance material(i.e Tungsten wire ) so if electric current passes through a high resistance it always produce heat. The heat produced here is about 2,000 to 3,300 K which emits the light of visible region.

But now a days INCANDESCENT LAMP is getting out from the service because:-

Efficiency of this bulb is very low because incandescent bulbs convert less than 5% of the energy they use into visible light rest of the electric energy used to convert heat produces infrared light which is not visible to human eye.

Life time of this lamp is less because due to heating of wire the particles of wire get evaporated and thus led to thinning of the wire .