Which of the following phenomena supports the theory that waves have a particle nature?

Analyze the question: We need the phenomenon that shows waves behaving like particles. Light and other electromagnetic radiation are normally treated as waves, so we look for the effect that only makes sense if they come in particle-like packets (photons).

Concept: Wave-particle duality works in two directions:

• Wave nature is shown by diffraction and interference. These are things waves do.
• Particle nature is shown when radiation behaves as discrete packets of energy (quanta or photons), with E = hf.

Check each option:

• A. Electron diffraction: Electrons are particles, and diffraction shows they behave like waves (de Broglie). This supports the wave nature of particles, which is the opposite of what the question asks.
• B. Photoelectric effect: When light shines on a metal surface, electrons are emitted only if the frequency is above the threshold frequency, no matter how intense the light is. Emission is instantaneous. Wave theory cannot explain this, but the photon idea can: each photon has energy E = hf, and hf = φ + ½mv²max (φ is the work function). This shows light behaving as particles, so it supports the particle nature of waves.
• C. Diffraction of light: This shows the wave nature of light.
• D. X-ray interference: Interference of X-rays also shows wave nature.

Answer: The photoelectric effect (B) is the phenomenon that supports the particle nature of waves.

Exam tip: Remember it this way: diffraction and interference = wave; photoelectric effect and Compton effect = particle. If the question asks about the particle nature of light, think "photoelectric."