Question

Which of the following is not true of fluorescent lights?

• A. They are gas-filled tubes
• B. The gas emits visible light when an electric current passes through it.
• C. The rays emitted by the gas are absorbed by the coating on the walls of the tubes
• D. The walls of the tubes are coated with a fluorescent substance.

Answer 1

The correct option is B

The gas emits visible light when an electric current passes through it.

Fluorescent lights

1. When an electric current flows through a tube filled with a fluorescent gas, the gas emits light under certain conditions. Tubes (also known as fluorescent lamps) and compact fluorescent lamps (CFLs) are gas-filled tubes. However, the light emitted by the gas is invisible, such as ultraviolet rays that kill microbes in water purifiers.
2. This light is absorbed by special materials that coat the walls of lamps and compact fluorescent lamps. This material emits light that we can see. A substance that absorbs light and emits light is called a fluorescent substance.

Hence Option b is correct.