Q 01/05

A rainbow caused by sunlight always appears in which part of the sky?

A) Directly opposite the Sun

B) Directly around the Sun

C) Due north of the observer

D) Wherever the rain is heaviest

Answer · why

A) Directly opposite the Sun

Directly opposite the Sun: the arc is centred on the point where the shadow of your own head falls, so you only ever see one with the Sun at your back...

Q 02/05

In a primary rainbow, which colour is on the outer edge of the arc?

A) Violet

B) Red

C) Green

D) Yellow

Answer · why

B) Red

Red light leaves the raindrop at the widest angle, so it forms the outside of the bow.

Q 03/05

From flat ground, no rainbow can appear when the Sun is where?

A) Near the horizon

B) Due east

C) High overhead

D) Due west

Answer · why

C) High overhead

High overhead: once the Sun climbs more than about 42° above the horizon the whole arc drops out of sight, which is why early morning and late afterno...

Q 04/05

Which three things happen to sunlight inside a raindrop to make a rainbow?

A) Reflection, ionisation and refraction

B) Diffraction, absorption and emission

C) Polarisation, Rayleigh scattering and fluorescence

D) Refraction, internal reflection and dispersion

Answer · why

D) Refraction, internal reflection and dispersion

Refraction, internal reflection and dispersion: light bends as it enters the drop, bounces off the back and bends again on leaving, and because each c...

Q 05/05

What happens to a rainbow when someone walks towards it?

A) It grows larger

B) It moves away

C) It fades to white

D) It splits in two

Answer · why

B) It moves away

It moves away: the bow is made by whichever drops sit at the right angle from the viewer's eye, so it shifts with every step, and no two people see qu...