Fundamentals
The core facts every aspirant should own — each a titled nugget with a real-world story, the concept in plain words, and a memory trick. Works even when the internet doesn't.
300 fundamentals
“Every power plant on Earth spins a magnet to make your electricity — Faraday's idea, scaled up.”
It is always perpendicular to velocity, so it can never change a charge's speed or energy.
“The solar panel and the smoke detector both run on Einstein-era quantum physics.”
A frequent error is thinking very bright low-frequency light can eject electrons. In reality, light ejects electrons from a metal only if its frequency exceeds a threshold, regardless of intensity.
Memory trick: frequency decides IF electrons come out; intensity only decides HOW MANY.
“The solar panel and the smoke detector both run on Einstein-era quantum physics.”
A frequent error is treating light purely as a wave when explaining the photoelectric effect. In reality, light comes in packets of energy E = hf = hc/λ.
Memory trick: higher frequency (bluer light) means more energetic photons.
“The solar panel and the smoke detector both run on Einstein-era quantum physics.”
A frequent error is using a positive energy for a bound electron — bound states are negative. In reality, electrons occupy quantised orbits; for hydrogen E_n = −13.6/n² eV.
Memory trick: the electron is most tightly bound (most negative) in n=1.
“The solar panel and the smoke detector both run on Einstein-era quantum physics.”
A nucleus weighs less than its parts; the missing mass becomes binding energy via E = Δmc².
Memory trick: fusion and fission both release the difference in binding energy.
“The solar panel and the smoke detector both run on Einstein-era quantum physics.”
A frequent error is ignoring the mass defect when computing nuclear energy. In reality, a nucleus weighs less than its parts; the missing mass becomes binding energy via E = Δmc².
Memory trick: fusion and fission both release the difference in binding energy.
“The solar panel and the smoke detector both run on Einstein-era quantum physics.”
A frequent error is expecting everyday objects to show wave behaviour (their λ is unimaginably small). In reality, every particle has a wavelength λ = h/p, significant only for tiny masses.
Memory trick: matter waves matter only at the electron/atom scale.
“The solar panel and the smoke detector both run on Einstein-era quantum physics.”
Energy of a photon. Use it when electromagnetic radiation of frequency f.
E = hf = hc/λ
“The solar panel and the smoke detector both run on Einstein-era quantum physics.”
Energy of the nth hydrogen level. Use it when hydrogen atom (Bohr model).
E_n = −13.6/n² eV
“The solar panel and the smoke detector both run on Einstein-era quantum physics.”
Energy equivalent of a mass defect. Use it when nuclear reactions.
E = Δmc²
“The solar panel and the smoke detector both run on Einstein-era quantum physics.”
De Broglie wavelength of a particle. Use it when particle with momentum p.
λ = h/p
“The solar panel and the smoke detector both run on Einstein-era quantum physics.”
Fission splits a heavy nucleus into lighter ones (reactors); fusion joins light nuclei into a heavier one (the Sun) — both release energy.