Download Visible Light - Eyemouth High School

Visible Light
Visible light is the only part of the electromagnetic spectrum that we are able
to detect with the naked eye. It allows us to form an image of the world around
us. The wavelength of visible light ranges from 390 nm (red) to Violet (700nm).
Each colour has its own wavelength (frequency). White light consists of all the
visible colours. When white light passes through a prism it slows down, if the
light enters at an angle it causes the light to change direction, this is called
refraction. Each colour refracts by a different amount. Higher frequency light
(shorter wavelengths) refract more than lower frequency signals (longer
wavelengths). This is evident in nature in the form of a rainbow.
Using a ray box, prism and screen (paper), pass light through the prism.
Copy the diagram above and list the colours displayed on the screen.
Colour Mixing
Seven colours can be clearly seen from prism, but in everyday life there are lots
of colours in all different shades. These can be produced by colour mixing. TV
sets use only 3 colours, red, green and blue to form all the colours displayed on
the screen.
Using the tri-coloured LED and the display box, copy and complete the table
below.
Primary Colours
Red + Blue
Red + Green
Green + Blue
Red + Green + Blue
Colour Produced
Emission Spectra
When a gaseous element is excited it gives out light. Each element gives out
light of specific frequencies (colours). By carefully examining the spectrum
produced from the source, each element present can be identified. This is how
astronomers can identify which elements are found in a star.
Using the spectrometer, look at spectra produced from sunlight. Now, dim the
light and look at spectra produced from a gas discharge lamp. Using, the
Spectrum reference sheets, can you identify the element?
Answer the following questions in sentences,
1. What colour in the visible spectrum has the highest frequency?
2. What colour has longest wavelength?
3. How is spectrum of light produced?
4. In a TV only 3 colours of light are used, how can we see numerous colour
when watching it?
5. How would you produce different shades of a specific colour?
6. What is a line emission spectra and why is it used by astronomers?
7. National 5 Only: Using the range of wavelengths for visible light
calculate the frequency range. n=nano (1x10-9).