GCSE Physics revision

Visible light (physics only)

Electromagnetic waves

AQA 4.6.2.6

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AQA student objectives

Learning pathway

All · Most · Some

ALL 🎯

Explain how absorption, transmission and reflection of different light wavelengths determine an object’s colour, including the effects of filters and opacity.

MOST 🎯🎯

Apply the scientific explanation of visible light to a relevant example.

SOME 🎯🎯🎯

Analyse a new situation involving visible light and explain the scientific reasoning.

Revision summary

Key knowledge

Read on screen, then print for Cornell-style active revision.

The Visible Light Spectrum

Visible light is the range of electromagnetic waves that our eyes can detect, and it forms a continuous spectrum of colours.
The colours of the spectrum, in order, can be remembered using the acronym ROY G BIV: Red, Orange, Yellow, Green, Blue, Indigo, Violet.
Red light has the longest wavelength and lowest frequency, whilst violet light has the shortest wavelength and highest frequency.

1. The Visible Light SpectrumAQA

Notes

Visible light is the range of electromagnetic waves that our eyes can detect, and it forms a continuous spectrum of colours.
The colours of the spectrum, in order, can be remembered using the acronym ROY G BIV: Red, Orange, Yellow, Green, Blue, Indigo, Violet.
Red light has the longest wavelength and lowest frequency, whilst violet light has the shortest wavelength and highest frequency.

White Light and Black

White light is not a single colour but a mixture of all the wavelengths in the visible spectrum combined.
Black is not a colour on the spectrum — it is simply the absence of light.
When white light passes through a glass prism, it splits into all the colours of the spectrum, producing a rainbow effect — this is called dispersion.

2. White Light and BlackAQA

Notes

White light is not a single colour but a mixture of all the wavelengths in the visible spectrum combined.
Black is not a colour on the spectrum — it is simply the absence of light.
When white light passes through a glass prism, it splits into all the colours of the spectrum, producing a rainbow effect — this is called dispersion.

How Opaque Objects Get Their Colour

Opaque objects do not transmit light; instead, they either absorb or reflect the wavelengths that hit them.
The colour we see is determined by the wavelengths of light that are reflected into our eyes.
A red apple appears red because it reflects red wavelengths and absorbs all other wavelengths.
An object that reflects both red and green wavelengths appears yellow, because red and green light combine to produce yellow.

3. How Opaque Objects Get Their ColourAQA

Notes

Opaque objects do not transmit light; instead, they either absorb or reflect the wavelengths that hit them.
The colour we see is determined by the wavelengths of light that are reflected into our eyes.
A red apple appears red because it reflects red wavelengths and absorbs all other wavelengths.
An object that reflects both red and green wavelengths appears yellow, because red and green light combine to produce yellow.

Transparent Objects and Colour

Transparent objects transmit most of the light that hits them, allowing us to see through them clearly.
The colour of a transparent object is determined by the wavelengths of light it transmits.
A green glass bottle appears green because it transmits green light whilst absorbing all other wavelengths.

Translucent Objects and Colour

Translucent objects transmit some light but scatter it in different directions, making objects viewed through them appear blurry.
The colour of a translucent object is determined by the combination of wavelengths it transmits and reflects.
A frosted glass bottle appears white and blurry because it scatters all wavelengths of light equally.
A green translucent bottle appears green and blurry because green wavelengths are transmitted and scattered whilst others are absorbed.

5. Translucent Objects and ColourAQA

Notes

Translucent objects transmit some light but scatter it in different directions, making objects viewed through them appear blurry.
The colour of a translucent object is determined by the combination of wavelengths it transmits and reflects.
A frosted glass bottle appears white and blurry because it scatters all wavelengths of light equally.
A green translucent bottle appears green and blurry because green wavelengths are transmitted and scattered whilst others are absorbed.

How Colour Filters Work

A colour filter is a material that only transmits certain wavelengths of light whilst absorbing or reflecting all others.
The primary colours of light in physics are red, green, and blue.
A primary colour filter only transmits light of one primary colour; for example, a green filter only allows green light to pass through.
If white light passes through a green filter and hits a white object, the object appears green because only green light reaches the eye.
If blue light hits a green filter, no light is transmitted and the object appears black, because the filter blocks the only wavelength the object reflects.

6. How Colour Filters WorkAQA

Notes

A colour filter is a material that only transmits certain wavelengths of light whilst absorbing or reflecting all others.
The primary colours of light in physics are red, green, and blue.
A primary colour filter only transmits light of one primary colour; for example, a green filter only allows green light to pass through.
If white light passes through a green filter and hits a white object, the object appears green because only green light reaches the eye.
If blue light hits a green filter, no light is transmitted and the object appears black, because the filter blocks the only wavelength the object reflects.

Non-Primary Colour Filters

Filters that are not primary colours transmit a specific range of wavelengths, including the primary colour wavelengths that combine to make that colour.
A yellow filter transmits red and green wavelengths (as well as yellow), because red and green light add together to produce yellow.
A violet filter transmits red and blue wavelengths (as well as violet), because red and blue are the primary colours that combine to make violet.

7. Non-Primary Colour FiltersAQA

Notes

Filters that are not primary colours transmit a specific range of wavelengths, including the primary colour wavelengths that combine to make that colour.
A yellow filter transmits red and green wavelengths (as well as yellow), because red and green light add together to produce yellow.
A violet filter transmits red and blue wavelengths (as well as violet), because red and blue are the primary colours that combine to make violet.

Absorption, Reflection, and Transmission — A Summary

Absorption occurs when an object takes in a wavelength of light, converting its energy so that colour is not seen by the observer.
Reflection occurs when a wavelength of light bounces off an object's surface and travels to the observer's eye, producing the perceived colour.
Transmission occurs when light passes through an object, and the transmitted wavelengths determine the colour seen through or from that object.

8. Absorption, Reflection, and Transmission — A SummaryAQA

Notes

Absorption occurs when an object takes in a wavelength of light, converting its energy so that colour is not seen by the observer.
Reflection occurs when a wavelength of light bounces off an object's surface and travels to the observer's eye, producing the perceived colour.
Transmission occurs when light passes through an object, and the transmitted wavelengths determine the colour seen through or from that object.