This clip takes apart a coin sorter and explains how the inside of it works. It uses electromagnets, currents, and disturbances in magnetic fields to determine the amount of metal in the coin.
Phil introduces the concept of electromagnets and explains the difference between them and regular magnets. He then demonstrates how to create a DIY electromagnet.
The Doctor hides himself in an elementary school to investigate an alien attack. As the teacher, he asks his students various physics questions to understand how much they know. One student, Milo, proves he's unusually smart and triggers the Doctor's interest.