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Study Notes: Colours - Reflection and Transmission

We see some objects by the light they reflect and others by the light they transmit.

The colour of an opaque object depends on the wavelengths of the light that it reflects to your eye.

A white piece of paper reflects all wavelengths. White light striking white paper with white light being reflected at varying angles.

A red piece of paper only reflects red wavelengths.

It will absorb the orange, yellow, green, blue and violet wavelengths.

White light striking red paper with red light being reflected in varying directions.

A blue piece of paper only reflects the blue wavelengths.

It will absorb the red, orange, yellow, green and violet wavelengths.

White light striking blue paper with blue light being reflected in varying directions.

The colour of a transparent object depends on the wavelengths of the light that it transmits to your eye.

The visible light passing through a clear piece of glass or plastic is unchanged.

White light striking a block of clear glass and passing through fully transmitted.

When white light shines on a piece of red glass, only the red wavelengths are allowed to pass through. The glass absorbs the other wavelengths.

White light striking a block of red glass with red light only being transmitted.

A blue piece of glass will absorb all colours except blue.

White light striking a block of blue glass with blue light only being transmitted.

Coloured glass or plastic can be used to change a beam of white light into a beam of the desired colour. The coloured glass or plastic is called a filter.

Filters are used in optical instruments to remove unwanted light.

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