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Pluto is officially no longer classed as a planet, and here's why. The International Astronomical Union defined three rules in 2005 that a celestial body (an object observable within space) must follow...

Einstein introduced the equivalence principle by saying "We ... assume the complete physical equivalence of gravitational field and a corresponding acceleration of the reference system".

We can understand this using an idea called the Kinetic Model of Gases. Basically, let's assume that every molecule in the gas is a tiny, tiny snooker ball whizzing around the containe...

This is a common IB question- fairly tricky the first time you com across it!

A typical transformer consists of an iron core with two coils wound around it - the primary and the secondary. Any current-carrying wire produces a magnetic field around it, but because the primar...