Physics Paper 2 Definitions

State what is meant by the photoelectric effect

The emission of electrons from the surface of a metal when electromagnetic waves (of a frequency greater than the threshold frequency) are incident on the metal

State the meaning of coherence

Waves/sources with constant phase difference

State what is meant by induced nuclear fission

A nucleus absorbs a slow-moving neutron, and splits into two smaller fragment nuclei and fast-moving neutrons

Explain the role of the moderator and control rods in a nuclear reactor

Moderator slows down fast-moving neutrons. They lose a significant amount of their kinetic energy colliding with the moderators. Control rods absorb the neutrons.

Describe the nature of the strong nuclear force

Acts between quarks/nucleons/hadrons

‘Short range’ force

Repulsive below 0.5fm

Attractive up to about 3fm

State the principle of superposition of waves

When two or more waves meet at a point in space, the resultant displacement is equal to the sum of the individual displacements of waves

Define electric potential at a point in space

Work done per unit charge in bringing a positive charge from infinity to that point

State Kirchhoff’s second law

Sum of e.m.f.is equal to the sum of p.d. in a loop, energy is conserved

State Faraday’s law of electromagnetic induction

Induced e.m.f. is equal to the rate of change of magnetic flux linkage

Define the work function of a metal

The minimum energy needed to remove an electron from the surface of a metal