A-Level Physics Flashcards

What is the photoelectric effect and what does it prove?

Answer: When light of sufficient frequency hits a metal surface, electrons are emitted, proving light behaves as particles (photons)

The photoelectric effect: photons must have energy ≥ the work function to eject electrons. The emission depends on frequency, not intensity, proving light has particle-like properties (photons with E = hf). This challenged classical wave theory.

What is the difference between elastic and inelastic collisions?

Answer: Elastic collisions conserve both momentum and kinetic energy; inelastic collisions conserve momentum but not kinetic energy (some KE is lost as heat or sound)

In elastic collisions, kinetic energy and momentum are both conserved (e.g., billiard balls). In inelastic collisions, momentum is conserved but kinetic energy is not — some is converted to heat, sound, or deformation.

What does the de Broglie equation describe?

Answer: The wave-like behaviour of matter: λ = h/mv (wavelength of a particle)

The de Broglie equation λ = h/p = h/mv links the wavelength of a particle to its momentum. It demonstrates wave-particle duality: all matter has associated wavelength. At low mass/high speed (electrons), the wavelength is measurable.

What is Ohm's Law?

Answer: Voltage = current × resistance (V = IR), for ohmic conductors at constant temperature

Ohm's Law states V = IR: the potential difference across a conductor is directly proportional to the current through it, provided temperature and other physical conditions remain constant. Materials that obey this are 'ohmic conductors'.

What is a standing wave and what conditions are needed to form one?

Answer: A stationary pattern formed by superposition of two identical waves travelling in opposite directions, forming nodes and antinodes

Standing waves form when two waves of equal frequency and amplitude travel in opposite directions and superpose. They have fixed nodes (zero displacement) and antinodes (maximum displacement). They form in resonating systems like strings, pipes, and cavities.

What is the significance of the Hubble constant?

Answer: It relates the recession velocity of galaxies to their distance (v = H₀d), showing the universe is expanding

The Hubble constant H₀ relates the recession velocity of galaxies to their distance: v = H₀d. Hubble's observation (1929) that more distant galaxies recede faster demonstrated that the universe is expanding, supporting the Big Bang theory.