Question

The glass bulb of electric bulb becomes black due to the deposition of vapor from the
A.Glass of the bulb
B.Metal filament
C.Gas in the bulb
D.Joint in the glass

Answer 1

Hint: Incandescent bulb or glass electric bulb uses tungsten as a filament which glows and gives the light. The tungsten is a Metal and melts at ${{3300}^{0}}C$ temperature. The bulb is used to enclose the filament to protect it from oxidation. These bulbs are not much efficient as they convert very less percentage of electrical energy into light energy. Most of the electrical energy is dissipated as heat energy.

Complete step by step Solution:
Light bulbs which we use in our day to day life firstly become brown then turn to black due to the presence of tungsten.
As tungsten is Metal filament it deteriorates with the time due to the heating particle of the Metal filament settling on the inside of the glass. Due to which the glass bulb becomes black one the period of time.

So the Option B is correct i.e. Metal filament.

Note: We should know that due to the heating effect or long use, metal deteriorates means the quality of metal becomes poor. Tungsten is used in filaments because it has melting temperature higher than any of the elements. The deterioration of metal results in the formation of greyish black appearance on the glass bulb which thereby results in the decreasing output of light. If the bulb is extremely black in color then it can be estimated that the bulb is at the verge to burn out. The lifetime of incandescent bulbs is less as compared to other types of bulbs. In today’s life such types of bulbs are mostly replaced by Light Emitting Diodes Lamps (LEDs).