AQA · A-Level · Physics
Course version: 7408 · Version from Sept 2016
Transmission-path media: metal wire, optic fibre, electromagnetic (radio,…
Full specification wording
Transmission media (A-level only): Transmission-path media: metal wire, optic fibre, electromagnetic (radio, microwave).
A transmission medium carries a signal from transmitter to receiver.
Checked against the AQA 7408 specification (opens in a new tab) on .
- Point 1 of 5
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A transmission medium carries a signal from transmitter to receiver. Metal wire, such as a coaxial cable, guides an electrical signal along conductors and is cheap and easy to connect, but suffers attenuation and can pick up interference. Optic fibre guides infrared or visible light by total internal reflection; it has very low attenuation and is immune to electromagnetic interference, but needs electro-optical converters and careful installation. Free-space electromagnetic links use radio waves, which diffract around obstacles and pass through walls, or microwaves, which need line of sight but support high bandwidth. Compare media by attenuation, bandwidth, interference immunity, cost and suitability for a given link.
What earns the marks
- Identify metal wire, optic fibre and free-space electromagnetic waves as transmission media and state that each guides or carries a signal between transmitter and receiver.
- Describe metal wire as guiding an electrical signal, with advantages such as low cost and simple connection, and disadvantages such as attenuation and susceptibility to electromagnetic interference.
- Describe optic fibre as guiding light by total internal reflection, with advantages such as low attenuation, high bandwidth and immunity to electromagnetic interference.
- Describe radio waves as free-space electromagnetic radiation that can diffract around obstacles and travel long distances, and microwaves as higher-frequency radiation suited to line-of-sight, high-bandwidth links.
- Compare media using criteria such as attenuation, bandwidth, interference, security, cost and installation requirements.
Common mistakes and how to put them right
Saying optic fibre carries an electrical current.
Put it right by stating that it guides light by total internal reflection.
Claiming radio waves cannot carry digital data.
Put it right by stating that radio links carry modulated signals, including digital information.
Treating microwaves as a different physical phenomenon from radio waves.
Put it right by stating that both are electromagnetic waves and differ mainly in frequency and propagation behaviour.
Exam tips
- When comparing media, name the criterion first and then apply it, for example attenuation: optic fibre has lower attenuation than metal wire.
- Link each medium to a realistic context, such as fibre for long-haul high-bandwidth links and radio for mobile or broadcast links.
- Use correct terminology such as total internal reflection, attenuation, bandwidth and electromagnetic interference.
Try the lesson
The start of the Transmission media (A-level only): Transmission-path media: metal wire, optic fibre, electromagnetic (radio, microwave). lesson, made from checked teaching notes for this specification point.
Have a go first
Which transmission-path medium carries information as infrared or visible light along a glass or plastic core?
Listen
A transmission medium carries a signal from transmitter to receiver. Metal wire, such as a coaxial cable, guides an electrical signal along conductors and is cheap and easy to connect, but suffers attenuation and can pick up interference. Optic fibre guides infrared or visible light by total internal reflection; it has very low attenuation and is immune to electromagnetic interference, but needs electro-optical converters and careful installation. Free-space electromagnetic links use radio waves, which diffract around obstacles and pass through walls, or microwaves, which need line of sight but support high bandwidth. Compare media by attenuation, bandwidth, interference immunity, cost and suitability for a given link. A strong answer earns marks for these points. Identify metal wire, optic fibre and free-space electromagnetic waves as transmission media and state that each guides or carries a signal between transmitter and receiver. Describe metal wire as guiding an electrical signal, with advantages such as low cost and simple connection, and disadvantages such as attenuation and susceptibility to electromagnetic interference. Describe optic fibre as guiding light by total internal reflection, with advantages such as low attenuation, high bandwidth and immunity to electromagnetic interference. Describe radio waves as free-space electromagnetic radiation that can diffract around obstacles and travel long distances, and microwaves as higher-frequency radiation suited to line-of-sight, high-bandwidth links. A common slip: Saying optic fibre carries an electrical current. Instead, stating that it guides light by total internal reflection. Exam tip: When comparing media, name the criterion first and then apply it, for example attenuation: optic fibre has lower attenuation than metal wire.
See it
Key words
Say what each word means before you turn the card.
Metal wire
Try answering aloud or in your head before turning the card.
Optic fibre
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Radio waves
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Microwaves
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See every definition
- Metal wire
- Guides an electrical signal along conductors, is cheap and easy to connect, but suffers attenuation and can pick up interference.
- Optic fibre
- Guides infrared or visible light by total internal reflection, with very low attenuation and immunity to electromagnetic interference, but needs electro-optical converters and careful installation.
- Radio waves
- Free-space electromagnetic radiation that diffracts around obstacles and passes through walls.
- Microwaves
- Free-space electromagnetic radiation that needs line of sight but supports high bandwidth.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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