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Computer Networks · Class 12 · Transmission Media · Wireless Media
networkstransmission media⏱️ 5 min read

Infrared Waves

Point a TV remote at the TV and it changes channel. Point it at the ceiling, hide it under a cushion, or try it from the next room, and nothing happens. The remote talks to the TV with infrared waves, and those three failures are exactly what infrared is like.

1What infrared waves are

Infrared waves
Infrared waves are electromagnetic waves of very high frequency, 300 GHz – 400 THz. They are used for short-distance, point-to-point communication and cannot pass through solid objects such as walls.

Infrared is just beyond the red end of the light we can see — “infra” means below, so infrared is below red in frequency. Your eyes cannot see it, but a phone camera often can: point a remote at your phone’s camera, press a button, and you may see its tip flash.

The TV remote

Put the remote somewhere and press a button. Drag sideways to turn.

Choose where the remote is, then press a button.

From your NCERT book, infrared waves:

  • Very high frequency.
  • Cannot penetrate solid objects such as walls.
  • Used for short-distance point-to-point communication, such as remote control to TV.

Being stopped by walls is not all bad. The infrared from your remote stays inside your room, so it never changes the channel on the neighbour’s TV, and nobody outside can pick it up.

Bluetooth is not infrared
NCERT’s table lists “Bluetooth-enabled devices” among the uses of infrared, but its own next section says Bluetooth uses the 2.4 GHz band — radio, not infrared. That is why a Bluetooth speaker keeps playing when your phone is in your pocket, which an infrared link could not do. Older phones did swap files and print by infrared, and that is the use NCERT means by mobile-to-mobile and mobile-to-printer.

Think of signalling with a mirror

Flash sunlight at a friend with a mirror and they see it at once — if they are near, in plain view, and nothing is in between. Step behind a wall and the signal is gone. Infrared behaves like light, because it is very nearly light.

2Advantages and disadvantages

✅ Advantages
  • Cheap and simple, like a TV remote.
  • Stays inside the room, so it does not disturb devices next door and is hard to eavesdrop on.
❌ Disadvantages
  • Works only over short distances.
  • Cannot pass through walls or other solid objects.
  • Sender and receiver must point at each other.

3Check yourself

Quick Check

Why does a TV remote not work from the next room?

Quick Check

Arrange the three wireless media from lowest to highest frequency.

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