Q 01/05

Which optical effect makes the clear daytime sky look blue?

A) Refraction

B) Total internal reflection

C) The Doppler effect

D) Rayleigh scattering

Answer · why

D) Rayleigh scattering

Rayleigh scattering. Air molecules scatter short blue wavelengths far more than long red ones, and at sunset the light crosses so much air that the bl...

Q 02/05

Which colour of visible light has a shorter wavelength than blue?

A) Green

B) Violet

C) Yellow

D) Red

Answer · why

B) Violet

Violet. Blue light runs from roughly 450 to 495 nanometres and violet is shorter still, so the 405-nanometre 'blue' laser that reads a Blu-ray disc re...

Q 03/05

What was the first artificial pigment, made more than 4,000 years ago by heating sand with ground minerals?

A) Prussian blue

B) Ultramarine

C) Egyptian blue

D) Cobalt blue

Answer · why

C) Egyptian blue

Egyptian blue. It glows strongly in infrared when lit, so museums can now photograph traces of it on ancient statues that look bare to the naked eye.

Q 04/05

Which organisation's flag shows a world map wreathed in olive branches on a light blue field?

A) NATO

B) The United Nations

C) The European Union

D) The Council of Europe

Answer · why

B) The United Nations

The United Nations. Its designers in 1945 chose blue to stand for peace, as the opposite of red, which they called the colour of war.

Q 05/05

Ultramarine, the most expensive Renaissance pigment, was ground from which stone?

A) Turquoise

B) Lapis lazuli

C) Sapphire

D) Azurite

Answer · why

B) Lapis lazuli

Lapis lazuli. Ground and washed into ultramarine, it could cost as much as gold, so Renaissance painters often saved it for the robes of the Virgin Ma...