A-Level Physics Flashcards

What is the strong nuclear force?

Answer: The short-range force that holds protons and neutrons together in the nucleus, overcoming electrostatic repulsion between protons

The strong nuclear force (strong interaction) acts between quarks and holds nucleons (protons and neutrons) together in the nucleus. It is very short-range (< ~3 fm) but extremely powerful, overcoming the electrostatic repulsion between protons.

What is the difference between alpha, beta, and gamma radiation?

Answer: Alpha (α) is a helium nucleus (stopped by paper); beta (β) is an electron (stopped by aluminium); gamma (γ) is a high-energy EM wave (reduced by thick lead/concrete)

Alpha particles (⁴₂He) are heavily ionising but have low penetration (stopped by paper or a few cm of air). Beta particles (electrons) have medium penetration (stopped by aluminium). Gamma rays are EM radiation, deeply penetrating, reduced by dense materials.

What is the Bohr model of the hydrogen atom?

Answer: Electrons orbit in fixed energy levels; when they transition between levels, they emit or absorb photons of specific frequencies

Bohr's model (1913) proposed electrons occupy fixed circular orbits (energy levels). When an electron drops to a lower level, it emits a photon with energy E = hf = E₂ − E₁. This explained the discrete line spectrum of hydrogen.

What is Faraday's Law of Electromagnetic Induction?

Answer: The induced EMF in a circuit is proportional to the rate of change of magnetic flux linkage through the circuit

Faraday's Law: EMF = −dΦ/dt (the negative sign comes from Lenz's Law). The induced EMF (and hence current) is proportional to how quickly the magnetic flux through a circuit changes. This is the basis of generators and transformers.

What is the principle of superposition of waves?

Answer: When two waves meet at a point, the resultant displacement is the algebraic sum of the individual displacements

The principle of superposition states that when two or more waves overlap, the total displacement at any point is the vector (algebraic) sum of individual displacements. This produces constructive interference (crests align) or destructive interference (crest meets trough).

What is the relationship between energy and mass in Einstein's special relativity?

Answer: E = mc²

Einstein's famous equation E = mc² shows that mass and energy are equivalent and interconvertible. A small mass corresponds to an enormous amount of energy (c ≈ 3 × 10⁸ m/s, so c² ≈ 9 × 10¹⁶). This underpins nuclear energy and particle physics.