Q 01/05

Roughly how fast does light travel through empty space?

A) About 300 km per second

B) About 3,000 km per second

C) About 300,000 km per second

D) About 30 million km per second

Answer · why

C) About 300,000 km per second

The exact figure is 299,792,458 metres per second, and the metre itself is now defined from it. That works out to about one billion kilometres per hou...

Q 02/05

Whose three laws of motion were first published in the Principia in 1687?

A) Johannes Kepler

B) Galileo Galilei

C) René Descartes

D) Isaac Newton

Answer · why

D) Isaac Newton

The Principia's full title is Philosophiae Naturalis Principia Mathematica, and it also set out universal gravitation. It was written in Latin.

Q 03/05

Which SI unit, symbolised by the Greek letter omega, measures electrical resistance?

A) Volt

B) Farad

C) Ampere

D) Ohm

Answer · why

D) Ohm

It honours the German physicist Georg Ohm, whose law links voltage, current and resistance. Omega was chosen because the letter O was easily confused ...

Q 04/05

What phenomenon makes the daytime sky look blue?

A) Rayleigh scattering

B) Refraction by water vapour

C) Fluorescence of ozone

D) Total internal reflection

Answer · why

A) Rayleigh scattering

Air molecules scatter short blue wavelengths far more than long red ones. The same effect leaves the low Sun looking orange at twilight once the blue ...

Q 05/05

At 20 °C, how fast does sound travel through air?

A) About 143 metres per second

B) About 343 metres per second

C) About 743 metres per second

D) About 1,043 metres per second

Answer · why

B) About 343 metres per second

That is roughly a kilometre every three seconds, which is why you count the seconds between lightning and thunder. In fresh water sound moves more tha...