Physics 2010 JAMB Past Questions - Question 45: In a discharge tube, most of the gas is pumped out so that electricity is conducted at

Correct Answer

B

Explanation

In a discharge tube, such as a fluorescent lamp or a neon sign, most of the gas is pumped out to create a low-pressure environment, which allows electricity to be conducted at a reduced pressure compared to atmospheric conditions. This low-pressure environment is achieved through a process called vacuum or gas evacuation.

When the gas pressure inside the tube is significantly lower than atmospheric pressure, it creates a condition where the gas atoms or molecules are more spread out, and there are fewer collisions between them. This is important for the operation of the discharge tube because it allows electrical discharge to occur more easily.

The low-pressure environment inside the discharge tube helps to promote the ionization of the gas atoms or molecules. When a voltage is applied across the electrodes of the discharge tube, it creates an electric field within the tube. The reduced pressure and the electric field make it easier for the electrons to gain enough energy to become free, creating a flow of charged particles, or an electric discharge. This discharge is what produces the visible light in fluorescent lamps or the colored glow in neon signs.

In summary, the evacuation of most of the gas from a discharge tube creates a low-pressure environment that facilitates the ionization of the remaining gas and the formation of an electric discharge, which is the basis for the operation of various gas-discharge devices.