Vacuum tubes were first called 'valves' because they act analogously to valves on water pipes.

Low-frequency radio waves travel better than high-frequency waves through salt water.

Covalent bonds form when two atoms share one or more pairs of electrons.

Charles Steinmetz (1865 - 1923) introduced the use of complex numbers in analyzing AC circuits.

Oddo–Harkins rule: elements with an even atomic number are more common than those with odd atomic number

Jupiter's Great Red Spot is twice the size of Earth.

FM radio is analogous to sending messages with a flashlight by varying the color of the light.

Physical constants and factorials johndcook.com/blog/2011/10/1…

AM radio is analogous to sending messages with a flashlight by varying the brightness of the light.

Differential equation for LRC circuit has exact same form as a mass-dashpot-spring mechanical system.

'Water continually dropping will wear hard rocks hollow.' -- Plutarch, c. 100 AD

Faraday discovered in 1831 that changing magnetic fields generate electric currents.

Stigler's law and Avogadro's number johndcook.com/blog/2012/01/0…

Oersted discovered in 1820 that electric currents generate magnetic fields.

'It's not so easy to free oneself from the idea that coordinates must have an immediate metrical meaning.' -- Albert Einstein

There were several competing theories of E&M during Maxwell's lifetime. Maxwell's theory triumphed a decade after he died.

Kinetic energy = 1/2 mass * velocity²

Maxwell published the laws of E&M as 20 equations. Now in modern notation they are four equations.

Technicium is mostly man-made, though traces have been found in nature.