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Properties of Visible Light
Properties of Visible Light Revision
Properties of Visible Light
Visible light is all of the wavelengths of electromagnetic radiation that we can see. The appearance of colours is determined by the wavelength of light.
Spectrum of Visible Light
The visible light spectrum is a section of the electromagnetic spectrum. Each colour has its own narrow band of wavelength and frequency. The visible light spectrum covers the wavelength range of \bold{380}\textbf{ - } \bold{700}\textbf{ nm}.
White light occurs when all of the colours of light are combined.
Colours
Objects that transmit light through them are either transparent or translucent. Transparent objects transmit all the the incident light through. Translucent objects transmit only some of the light through.
Objects that transmit none of the incident light are called opaque.
Colour filters only transmit certain wavelengths. They absorb the other wavelengths.
For example, a red colour filter will only transmit wavelengths of light between 625 \text{ nm} and 740 \text{ nm}. All other wavelengths of light will be absorbed by the filter.
Similarly, an object of a certain colour only reflects that colour. All other colours of light are absorbed by the object. We only see the reflected wavelengths and hence the object appears that colour.
For example, a red cube absorbs all wavelengths of light except wavelengths in the range 625 \text{ nm} to 740 \text{ nm}. We only see this reflected light so the object appears red.
Properties of Visible Light Example Questions
Question 1: Does a red light ray or a blue light ray have a longer wavelength?
[1 mark]
The red light ray has the longer wavelength.
For red light, wavelengths range from 625 \text{ nm} to 740 \text{ nm}.
For blue light, wavelengths range from 440 \text{ nm} to 510 \text{ nm}.
Question 2: Define each of the following words in terms of the amount of light that can pass through them:
a. Opaque
b. Translucent
c. Transparent
[3 marks]
a. Opaque objects do not transmit any light through them.
b. Translucent objects transmit some light through them.
c. Transparent objects transmit all light through them.
Question 3: Explain how a blue colour filter turns white light into blue light.
[3 marks]
White light contains all colours of visible light.
The blue filter only transmits blue wavelengths.
All other wavelengths are absorbed by the filter.
Question 4: Why does grass appear green? In your answer, refer to the interactions between different wavelengths of visible light and the grass.
[3 marks]
The grass reflects green wavelengths of light.
All other wavelengths of light are absorbed by the grass.
We only see the reflected green light.
