Which of the following experimental observations provides direct evidence for the existence of discrete electron energy levels in isolated atoms?
The continuous spectrum of electromagnetic radiation emitted by a blackbody at high temperature.
The emission of photons of only specific, discrete wavelengths from a low-pressure gas in a discharge tube.
The release of electrons from a metal surface only when the incident radiation exceeds a specific threshold frequency.
The diffraction pattern produced when a collimated beam of electrons passes through a thin metal foil.
31 exam-style questions on AQA A Level Physics Electromagnetic radiation and quantum phenomena, covering The photoelectric effect, Collisions of electrons with atoms, Energy levels and photon emission, and Wave-particle duality. Each one has a worked solution and a mark scheme showing where the marks go.