Electric bulb:
It is an electric device that provides light when an electric current is passed through it.
Construction:
A bulb has an outer case of glass that is fixed on a metallic base as shown in the figure. A thin wire is fixed in the middle of the glass case which gives off light. This thin wire is called the filament. This filament is fixed to two other thick wires to provide support to the filament. One of two thick wires is connected to the metal case at the base of the bulb. The other thick wire is connected to the metal base. The base and the metal tip at the base are the two terminals of the bulb. These two terminals are so placed that they do not touch each other.
Working:
On connecting the bulb in an electric circuit electric current begins to flow through the filament of the bulb as a result of which the filament first becomes hot and then on more heating the temperature increases and it becomes red hot and ultimately white-hot and starts emitting light.
