What type of electromagnetic radiation is used in the remote control of a television?

The correct answer is A, infrared.

A TV remote sends a beam of infrared light, usually at a wavelength near 940 nm, from an LED at its tip. The signal is pulsed in a coded pattern, and a photodiode in the TV decodes it. Infrared is used because it is invisible to the eye, cheap to generate, and does not pass through walls, so the signal stays within the room.

• Ultraviolet (B): Lies beyond violet, with wavelengths shorter than visible light. It is used for sterilisation, forensic fluorescence and in tanning lamps, but it harms eyes and skin and is not used for remote signalling.
• Visible (C): Our eyes see only this narrow band. A remote using visible light would be distracting, and ordinary room lighting would interfere with the signal.
• None of the above (D): Incorrect, because infrared fits the description.

The core concept is the electromagnetic spectrum, ordered by wavelength and frequency: radio, microwave, infrared, visible, ultraviolet, X-ray, gamma. Know the uses of each band. Mains links this to applications of physics in daily life and to technologies such as thermal imaging and optical fibre communication.

Trap: Students pick radio waves or microwaves because they think of wireless signals. A conventional TV remote is a short-range infrared device, not a radio device.