AQA · GCSE · Combined Science

    Course version: 8464 · Version from Sept 2018

    Visible light – fibre optic communications

    Full specification wording

    Uses and applications of electromagnetic waves: visible light – fibre optic communications

    Visible light is the narrow band of the electromagnetic spectrum detected by the human eye.

    Checked against the AQA 8464 specification (opens in a new tab) on .

    • Point 5 of 8
    • 2 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    Visible light is the narrow band of the electromagnetic spectrum detected by the human eye. In fibre optic communication, light carrying a signal travels along a thin glass or plastic fibre. The light rays bounce back and forth off the inside walls of the fibre, reflecting completely so that the light stays inside the core, even around bends. Pulses of light encode digital information, allowing signals to travel long distances with little loss for telephone and internet networks.

    What earns the marks

    • Visible light is the part of the electromagnetic spectrum detected by the human eye.
    • Optical fibres are thin strands of glass or plastic used to transmit pulses of light over long distances.
    • Light rays travel along the fibre by reflecting completely off the inside surface of the fibre.
    • (HT only) Visible light is suitable for optical fibres because its high frequency allows it to carry a large amount of information per second.
    • (HT only) Visible light is also suitable because it undergoes total internal reflection with low signal loss in glass or plastic.

    Common mistakes and how to put them right

    • Saying light reflects off the outside of the fibre.

      Put it right by stating that light reflects off the inside surface of the fibre.

    • Thinking light travels in a perfectly straight line through a bent fibre.

      Put it right by explaining that light travels in straight lines but bounces off the internal walls to navigate bends.

    • Confusing the use of visible light in fibres with radio waves in aerials.

      Put it right: Visible light is contained within the fibre, whereas radio waves are broadcast through the air.

    • (HT only) Stating visible light has a longer wavelength than microwaves.

      Put it right by remembering visible light has a shorter wavelength and higher frequency, which increases its data capacity.

    Exam tips

    • State that light reflects off the inside walls of the optical fibre to travel along it.
    • Remember that optical fibres use pulses of light to transmit digital information.
    • (HT only) When asked to explain suitability, link the high frequency and short wavelength of visible light to the large amount of information it can carry.

    Try the lesson

    The start of the Uses and applications of electromagnetic waves: visible light – fibre optic communications lesson, made from checked teaching notes for this specification point.

    Have a go first

    Which type of electromagnetic wave is carried along a fibre optic cable to send telephone and internet signals?

    Listen

    Visible light is the narrow band of the electromagnetic spectrum detected by the human eye. In fibre optic communication, light carrying a signal travels along a thin glass or plastic fibre. The light rays bounce back and forth off the inside walls of the fibre, reflecting completely so that the light stays inside the core, even around bends. Pulses of light encode digital information, allowing signals to travel long distances with little loss for telephone and internet networks. A strong answer earns marks for these points. Visible light is the part of the electromagnetic spectrum detected by the human eye. Optical fibres are thin strands of glass or plastic used to transmit pulses of light over long distances. Light rays travel along the fibre by reflecting completely off the inside surface of the fibre. HT only) Visible light is suitable for optical fibres because its high frequency allows it to carry a large amount of information per second. A common slip: Saying light reflects off the outside of the fibre. Instead, stating that light reflects off the inside surface of the fibre. Exam tip: State that light reflects off the inside walls of the optical fibre to travel along it.

    See it

    A vertical flowchart with seven boxes connected by downward arrows. The top box reads 'Pulses of light encode digital information' and points to 'Light enters thin glass or plastic fibre'. That points to 'Light rays bounce back and forth off the inside walls of the fibre', which points to 'Light reflects completely so it stays inside the core'. That points to 'Light stays inside the core even around bends', which points to 'Signals travel long distances with little loss'. The final box reads 'Telephone and internet networks'.
    It shows how pulses of light travel along an optical fibre by reflecting off the inside walls, allowing signals to travel long distances with little loss for telephone and internet networks.

    Put it in order

    Put these steps in the order they happen.

    1. 1. Telephone and internet networks
    2. 2. Signals travel long distances with little loss
    3. 3. Light rays bounce back and forth off the inside walls of the fibre
    4. 4. Light stays inside the core even around bends
    5. 5. Pulses of light encode digital information
    6. 6. Light enters thin glass or plastic fibre
    7. 7. Light reflects completely so it stays inside the core

    Key words

    Say what each word means before you turn the card.

    Visible light

    Try answering aloud or in your head before turning the card.

    Optical fibres

    Try answering aloud or in your head before turning the card.

    See every definition
    Visible light
    The narrow band of the electromagnetic spectrum detected by the human eye.
    Optical fibres
    Thin strands of glass or plastic used to transmit pulses of light over long distances.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A vertical flowchart with seven boxes connected by downward arrows. The top box reads 'Pulses of light encode digital information' and points to 'Light enters thin glass or plastic fibre'. That points to 'Light rays bounce back and forth off the inside walls of the fibre', which points to 'Light reflects completely so it stays inside the core'. That points to 'Light stays inside the core even around bends', which points to 'Signals travel long distances with little loss'. The final box reads 'Telephone and internet networks'.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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