Electromagnetic Waves in Communication (BTEC Unit 1 Revision)

Electromagnetic Spectrum

If you’ve ever sent a text, connected to Wi-Fi, or used Bluetooth headphones — you’ve used electromagnetic (EM) waves.

But in your exam, it’s not enough to just know what they are — you need to understand why different types are used for different communication methods.

The Big Idea: Frequency Matters

All electromagnetic waves travel at the same speed (the speed of light), but they differ in:

• Frequency (Hz) → how many waves pass per second

• Wavelength (m) → distance between peaks

These properties affect how the wave behaves.

Key rule for exams:

• High frequency → carries more data but shorter range

• Low frequency → travels further but carries less data

1. Satellite Communication

Uses: Microwaves, but why?

• Can pass through the atmosphere

• Not absorbed much by air

• Travel long distances

A signal is sent from Earth → satellite → back to Earth. Microwaves are ideal because they are not reflected by the ionosphere

2. Mobile Phones

Uses: Microwaves (UHF range), but why?

Microwaves can carry large amounts of data (calls, video, internet). Therefore it’s suitable for short-range transmission between masts. However the limitations of using microwaves are:

• Need many cell towers

• Signal can be blocked by buildings

Cell towers are high to avoid interference

3. Bluetooth

Uses: Radio waves (low power microwaves), but why?

Bluetooth communications are designed for short distances (≈10 m). They also use low energy for example in Wireless headphones and Smartwatches. Overall this method of communication is Lower power = safer and energy efficient, but limited range

4. Infrared

Uses: Infrared radiation but why?

Infrared is Used for very short-range communication, and Requires line of sight. Examples include use in TV remotes and sensors. Limitations of this method of communication are that infrared Cannot pass through walls and that the radiation is Easily absorbed. Infrared is used when direct, secure communication is needed

5. Wi-Fi

Uses: Microwaves (higher frequency than Bluetooth, but why?

Microwaves Can carry large data volumes. This Works over moderate distances (≈20–50 m). However, Limitations are that Walls reduce signal strength and that Interference is possible. Overall it has Higher frequency than Bluetooth = faster data transfer.

Summary table

Technology	Type of EM Wave	Key Advantage	Key Limitation
Satellite	Microwaves	Long distance transmission	Requires clear path
Mobile Phones	Microwaves	High data capacity	Needs many masts
Bluetooth	Radio waves	Low energy, safe	Very short range
Infrared	Infrared	Secure, direct communication	Needs line of sight
Wi-Fi	Microwaves	Fast data transfer	Limited by obstacles

How This Comes Up in Exams

You may be asked to:

• Explain why a certain wave is used

• Compare two communication methods

• Link frequency to function

Example question:

Explain why microwaves are used for satellite communication (3 marks)

✅ Model answer:

• Microwaves can pass through the atmosphere

• They are not reflected by the ionosphere

• They can travel long distances with little absorption