Question

Which of the following are properties of filament of bulb?
A. High melting point
B. Low melting point
C. Non-corrosive
D. High temperature resistance

Answer 1

Hint: In order to solve this question we have to understand that an incandescent lamp or light bulb is in the shape of a globe having filament made from tungsten. Filament gets heated due to electricity and hence it glows which results in glowing of lamp or bulb. Also the filament is stored in a vacuum that means inside an incandescent bulb, it is done to prevent filament from catching fire.

Complete answer:
The Filament used in bulb must have some properties that allow its electrons to jump from lower state to excited state without distorting filament so it must have following properties.
High Melting point: This means filament of bulb used must not breakdown as current passes so melting point must be high so that it can withstand high temperature

Non corrosive: The filament must be free from oxidation in an inert gas medium because if oxygen comes in contact combustion reaction could take place and filament could be burnt so it must be non- corrosive.

High Temperature resistance: Filament must not expand on heating so it must have low thermal coefficient so that it could not stretch more. Since temperature resistance is inversely proportional to thermal coefficient so filament must have high thermal resistance

So the correct options are A,C and D.

Note: It should be remembered that filament glows because of electron transition. Actually what happens is upon heating the current electron in the lower energy state gets excited to higher energy states so upon d-excitation releases light made of photons having energy so the bulb glows. Tungsten is used because of its extensive properties.