Radio Waves
Turn on an FM radio in a moving car, inside your house, or in a village far from the city, and the same station plays. Nobody pointed an antenna at you, and no cable runs to your radio. That is what radio waves are good at.
1Wireless media, in one line
In wireless media, data travels through the air as electromagnetic waves, sent and received by antennas. Different waves are told apart by their frequency — how many times the wave goes up and down each second, in hertz (Hz), as you saw in Bandwidth. Your syllabus has three kinds: radio waves, microwaves and infrared waves, from the lowest frequency to the highest.
2Radio waves
Choose where someone is listening. Drag sideways to turn.
From your NCERT book, radio waves:
- Omni-directional: move in all directions.
- 300 KHz – 30 MHz can travel long distances.
- Susceptible to interference.
- 3 – 300 KHz can penetrate walls.
- Used in AM and FM radio, television, cordless phones.
Because they go everywhere, the sender and receiver do not have to face each other or even see each other. That makes radio waves ideal for broadcasting — one station, and anyone in range can listen.
Think of a school bell
3Advantages and disadvantages
- Travel in all directions: antennas need not point at each other.
- Can travel long distances.
- Pass through walls, so they work indoors.
- No cables to lay, even across rivers or hills.
- Susceptible to interference from other signals.
- Anyone in range can pick them up, so they are less secure.
- Lower information-carrying capacity than microwaves.
4From the board papers
▶Show the answer
(A) Radio Waves. NCERT lists AM and FM radio as a use of radio waves.
▶Show the answer
Any two of radio waves, microwaves and infrared waves.
5Check yourself
What does it mean that radio waves are omni-directional?
Which of these uses radio waves, according to your NCERT book?