If all wavelengths are absorbed the objects appears black.

The idea

A black surface absorbs all, or nearly all, of the visible wavelengths that land on it, so almost no light is reflected back to your eye and you see black. Black is the absence of reflected light, not a colour being sent out. Because a black object has nothing to reflect whatever colour you shine on it, it stays black under red, green or blue light, unlike a white or coloured object. The absorbed energy is transferred to the internal energy store of the surface, so black objects warm quickly: in the AQA cube experiment matt black gave the largest temperature rise, 6.5 °C, against 2.0 °C for shiny white. Surface texture matters as well as colour, so matt black absorbs more than shiny black.

What earns the marks

• Stating that a black surface absorbs all, or nearly all, of the visible wavelengths.
• Stating that almost no light is reflected to the eye.
• Stating that a black object appears black under any colour of light.
• Concluding from data that the matt black surface absorbs the most and so shows the greatest temperature increase.

Common mistakes and how to put them right

• Writing that a black object reflects black.

• Giving a conclusion such as 'black absorbs infrared' without saying more than what.

• Comparing a matt surface with a shiny surface of a different colour, so changing two variables at once.

• Naming shiny black as the best absorber when the data show matt black is.

Exam tips

• Quote the figures from the table when you are asked for a conclusion.
• Compare like with like: matt against shiny of the same colour, black against white of the same finish.
• Say 'almost no light is reflected' rather than 'it has no colour'.