Colour Spectra 4t ESO Physics

1. Physics
Level 4th ESO (10th grade)
Institut La Sénia

2. Coloured liquids Coloured Lights Optical fiber
Console Visible Spectrophotometer Cuvette
EQUIPMENT

3. Solutions of water and food colouring
Spectra of coloured liquids

4. Visible spectrophotometers produce white light which is
dispersed to form the visible spectrum
The dispersed light passes through the cuvette where the
solution to be measured is placed
The solution absorbs part of the spectrum except its colour.
This is called ABSORBANCE and it is measured by the detector
Spectra of coloured liquids

5. Results for 1-colour solutions
RED SOLUTION absorbs all the
spectrum except red
BLUE SOLUTION violet and green
slight absorption, blue no absorption
YELLOW SOLUTION yellow, orange
and red register the least absorbance
WATER: colourless, no absorption

6. Results for 2-colour mixtures
We obtain a green colour which is where we see the least absorbance
The result is an orange colour with minor absorption at yellow, orange and
red wavelengths
Yellow + blue
Yellow + red

7. Results for 2-colour mixtures
We obtain kind of a violet solution. The least absorbance is
detected both violet and red part of the visible spectrum
Red + Blue

8. Coloured light collected by the optical fiber and analysed in
the spectrophotometer
Spectra of coloured light

9. The input light is dispersed inside the spectrophotometer
The spectra show the INTENSITY of each colour which is
measured by the detector
Spectra of coloured light

10. Results for 1-colour lights
BLUE LIGHT
RED LIGHT
GREEN LIGHT
Mainly blue intensity and some green
The highest intensity for orange but some
blue it is also included
Green is clearly spotted

11. Results for white light
BICYCLE FRONT
LIGHT
MOBILE PHONE
FLASH LIGHT
Observing the two lights before getting the spectra: the bicycle
light has got an orange tonality and the flash light is bright white
Therefore, we see that the red colour is present in the bike light
spectrum and gives this noticed tonality, while the flash light has a
high intensity band in blue colour

12. Results for more-colours light
RED, BLUE AND GREEN LIGHT
RED AND GREEN LIGHT
The two primary light colours together produce yellow and the spectrum shows it
The result is white light. The spectrum shows one band for each colour

13. THANKS