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COLOURPhysicsLevel 4th ESO (10th grade)Institut La Snia

NEWTONS EXPERIMENTWe used a head light (with a narrow slit)

A shine a ray of white light through a glass prism and on to a white screen

We could see the seven colours of the spectrum

2

NEWTONS COLOUR WHEEL

Spin a colour wheel quickly so that the colours appear to be mixed together

How does a prism disperse white light into a spectrum?Different colours of light have different wavelengths.All colours of light travel at the same speed in a vacuum. When they enter a transparent substance like glass, they all slow down but by different amounts.Because they slow down by different amounts, different colours are refracted through different angles.

For example: Violet: have the shortest wavelength, is refracted through the largest angle. Red: have a longer wavelength, is deviated through a smaller angle.

The electromagnetic spectrum

Properties of all electromagnetic waves:They transfer energy from one place to another.They are all transverse waves.They can all be reflected, refracted, diffracted.They can all travel through a vacuum (space).They all travel at 300 000 000 m/s in a vacuum.Wave speed = frequency x wavelength.The shorter the wavelength (the higher the frequency), the more dangerous they are.

Subtraction of colour 1What happens when white light shines on coloured objects?

Blue objects absorb ROYGV and leave B to be reflected to our eyes. Red leave R reflected.Black objects absorb all the colours and white absorb none.

Subtraction of colour 2Some experiments. We put FILTERS in front of a white light.

WITHOUT FILTERSRED FILTER

GREEN FILTERRED AND GREEN FILTERSALL THE FILTERS

Subtraction of colour 3More experiments, we looked at coloured objects in coloured lights. Our results were:

COLOUR OBJECTFILTERED LIGHTAPPEARANCEWhiteRedRedBlueRedLight red/violetWhiteYellowYellowBlueYellowLight yellow

Pictures of the experiments:

In practice most filters are not perfect

Addition of colour We did an experiment. We had green, blue and red lights. And we made some variations. For example, we put together two different filters or all of them together.

BLUE + REDGREEN + REDBLUE + GREEN

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