COLOURSSPECTRA

PhysicsLevel 4th ESO (10th grade)

Institut La Sénia

Coloured liquids Coloured Lights Optical fiber

Console Visible Spectrophotometer Cuvette

EQUIPMENT

Solutions of water and food colouring

Spectra of coloured liquids

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

Spectra of coloured liquids

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

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

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

Coloured light collected by the optical fiber and analysed in the spectrophotometer

Spectra of coloured light

The input light is dispersed inside the spectrophotometerThe spectra show the INTENSITY of each colour which is measured by the detector

Spectra of coloured light

Results for 1-colour lightsBLUE 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

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

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

THANKS