Quantum Duality: 16 MCQs with answers

Double-slit experiment

The double-slit experiment shows interference and diffraction, which are wave phenomena. The photoelectric effect and Compton scattering demonstrate particle nature.

Light behaves as discrete packets of energy (photons)

The photoelectric effect showed that light energy comes in quantized packets (photons), each with energy proportional to frequency (E = hf).

Albert Einstein

Einstein explained the photoelectric effect in 1905 by proposing light quanta (photons), for which he later won the Nobel Prize.

Everything exhibits both wave and particle properties depending on the experiment

Wave-particle duality means that quantum objects (like light and electrons) show wave-like or particle-like behavior depending on how they are observed.

Light exhibits interference, proving it is a wave

Young's experiment showed interference fringes, which only occur for waves, establishing the wave nature of light.

False

De Broglie's hypothesis and experiments like Davisson-Germer show that matter (electrons, etc.) also exhibits wave-particle duality.

They form an interference pattern over time

Even single electrons build up an interference pattern over time, showing that each electron interferes with itself—demonstrating wave behavior for matter.

All matter has a wavelength given by λ = h/p

De Broglie proposed that every particle has a wavelength inversely proportional to its momentum, extending wave-particle duality to matter.

Davisson-Germer experiment

Davisson and Germer observed electron diffraction from a nickel crystal, confirming de Broglie's matter waves.

E = hf

The photon energy is directly proportional to its frequency, with Planck's constant h as the proportionality constant: E = hf.

Photoelectric effect

The photoelectric effect requires the concept of photons—discrete energy packets—to explain why electrons are emitted only above a threshold frequency.

λ = h/p

De Broglie's relation is λ = h/p, where h is Planck's constant and p is momentum. This gives the wavelength for any matter particle.

It sets the scale for quantization of energy

Planck's constant (6.626×10⁻³⁴ J·s) is the fundamental quantum of action; it appears in E=hf and λ=h/p, determining the graininess of nature.

False

Measurement collapses the wavefunction, destroying the superposition and thus the interference pattern—this is the observer effect.

The interference pattern disappears

Measurement collapses the wavefunction, destroying the superposition and thus the interference pattern—this is the observer effect.

Its square gives the probability density of finding a particle

The wave function (ψ) is a mathematical description; |ψ|² gives the probability of finding the particle at a location—it's not a physical wave.