Tag: simple electric circuits

Incandescent light bulbs use heat generated by the resistance of the filament to create light. to get white light you need the filament to reach 2700-3300 K to give off white yellow light.

The reason tungsten is used is because it has the highest melting temperature of any element at 3600 K.

To generate a lot of heat you need a big resistance. Resistance(R) is dependent on resistivity ($\rho$) but also on the length (l) of the wire and the width (w).

R $=\dfrac{\rho \times l}{A} $

Having a big resistivity helps to create a big resistance but since you can change the thickness and length of the filament in light bulb (the filament is looped to increase the length) you can control the resistance. 

Incandescent light bulbs are filled with an inert gas like nitrogen, argon, or krypton - so that the filament doesn't catch fire. Early ones were a vacuum. Flourecent lamps are filled with an inert gas plus mercury vapour or neon, which glows ultra-violet when charged. The inside of the bulb is painted to give it colour.

The filament of bulb has high resistance so the filament heats up due to current passing through (${ I }^{ 2 }R$ losses )  and due to its heating , the electrons change their energy states and photons in visible spectrum are emitted . more the losses , more would be the light.that's why filament of bulb offers high resistance.

The leading wire is usually made with conductors such as copper and aluminium, therefore have less resistance than the filament which is usually made with tungsten and has a high resistance.
Due to this the power lost P $ =I^{2}R $ is greater for filament which is visible as light(and also heat).

Filaments in incandescent light bulbs are made of tungsten. When electric current goes through the filament, the filament glows. It may also be known as the electron emitting element in a vacuum tube. To make the bulb produce more light,the filament is usually made of coils of fine wire, also known as the coiled coil.

Tungsten metal is selected for making filaments of lamp bulbs because tungsten can sustain high temperatures and it has high melting point, combined with the fact that it also has high resistivity. They do not oxidize easily at high temperatures.

The filament heats and gives off light. Over time, the filament oxidizes and becomes more and more brittle, until it breaks apart and the bulb goes out. ... Tungsten gains resistance as it heats. Resistance is the amount of 'push back' a material has against an electric current

Resistance of 25 w bulb, ${R _1} \Rightarrow \frac{{{{220}^2}}}{2} = 1936\Omega $