Question

An electric bulb is filled with:
A. Hydrogen
B. Oxygen and hydrogen
C. Electrical energy
D. Nitrogen and Argon

Answer 1

Hint: As we all know that the tungsten filament is used in the bulb. It has the property to evaporate in a vacuum and since it evaporates it catches fire as the temperature of the tungsten filament is increased, that is when it becomes hot.

Complete step by step answer:
We know that incandescent lights like bulbs are filled with gases that are inert. The gases can be such that it cools the filament and carries away all the heat from it. These types of inert gases reduce the evaporation rate of the tungsten filament compared to the condition at which it is operating in a vacuum. If we don’t use these gases, then the temperature of the tungsten filament will increase and the filament’s atoms would boil away which ultimately reduces the life of the bulb.
We know that nitrogen is used since the hot filament does not react with nitrogen and it stops the arcing between the filament supports. Argon is used since it is chemically inert and since it is having high vapor pressure which in the end reduces the evaporation of the filament. Also, argon has a very low thermal conductivity which reduces the cooling conduction of the filament.
Generally, 93% Argon and 7% Nitrogen as a combination is used while filling the incandescent light bulbs. Here nitrogen assists argon as argon has very low breakdown voltage.

$\therefore$ The correct option is (D).

Note:
We also know that nowadays certain halogen bulbs are used in which argon is used with a small amount of halogen and the halogen is mainly bromine and iodine. When halogen is evaporated, it combines with tungsten forming a halogen-tungsten compound which dissociates when comes in contact with the filament of tungsten and it relocates the evaporated tungsten to the filament.