Скачать или смотреть Quantum Physics | LEC-71 | A2-Level Physics 9702 | Basics to Brilliance | Sir Talha | 19th feb 2026

In A2 Physics, quantum physics describes the behaviour of matter and radiation at very small scales, such as atoms, electrons and photons. It shows that energy is not continuous but is transferred in discrete packets called quanta. For electromagnetic radiation, these packets are called photons. The energy of a photon depends on the frequency of the radiation, meaning higher-frequency radiation carries more energy.
One key idea in quantum physics is the photoelectric effect, which demonstrates that light can behave like particles. When light shines on a metal surface, electrons are emitted only if the light has a minimum frequency known as the threshold frequency. Increasing the intensity increases the number of emitted electrons but does not increase their maximum energy, showing that energy depends on frequency, not intensity.
Quantum physics also explains wave–particle duality, the idea that particles such as electrons can show both wave-like and particle-like behaviour. This is supported by electron diffraction experiments. Another important concept is the existence of discrete energy levels in atoms. Electrons can only occupy specific energy levels, and when they move between levels, they absorb or emit photons with specific energies, producing line spectra. These ideas form the basis of modern atomic theory and many technologies such as lasers and semiconductors.