AL Physics Paper 1 Definitions

Hadron

A particle that experience the strong (nuclear) force/interaction..

Baryon

A particle composed of three quarks.

Meson

A particle composed of a quark and antiquark.

Work function

The minimum energy required by an electron to escape from a metal surface.

Ionisation Energy

The minimum energy to remove an electron from the ground state of an atom.

Excited atom / Excitation

An electron has moved to a higher energy level/orbital/state

Isotopes

Isotopes are variations of an element that have the same proton/atomic number but different number of neutrons.

Atomic number

The number of protons in the atom.

Nucleon number

The number of protons and neutrons.

Annihilate

Particle and antiparticle meet and convert into two or more photons.

Ground state

When electrons/atoms are in their lowest/minimum energy state.

Threshold frequency

The frequency of radiation/photons below which no electrons are emitted from the surface of the metal.

Wave particle duality

Show properties that are both wavelike and like particles.

Progressive wave

A wave transfers energy from one point to another without transferring material

Longitudinal wave

Direction of oscillations of particles is parallel to direction of energy propagation. Requires a medium.

Transverse wave

Direction of oscillations (or movement of particles) perpendicular to direction of energy propagation. Can be polarised.

Monochromatic

Single wavelength (or frequency)

Coherent

Waves/source have constant phase difference (and must also be monochromatic - same wavelength/frequency)

Amplitude

Maximum displacement from the equilibrium position.

Frequency

Number of waves/complete cycles/wavelengths passing a point/produced per second.

Potential Divider

A combination of resistors in series connected across a voltage source.

Current

The rate of flow of charge

Resistance

The resistance of a device is defined by R = V/I where R is the resistance of the device, V is the potential difference across it and I is the current through it.

EMF

Emf is the workdone or energy transferred by a a battery/voltage source per unit charge

Superconductor

A material which has zero resistivity below the critical temperature.

Critical Temperature

The temperature below which a material has zero resistivity.

Non-Ohmic

Resistance is not constant.

Internal resistance of a battery

The resistance of the materials within the battery

Hooke's Law

The force needed to stretch a spring is directly proportional to the extension of the spring (from its natural length) up to the limit of proportionality.

Elastic behaviour

Returns to its original length/shape/zero extension when the force is removed. No permanent extension.

Plastic behaviour

Permanent deformation / permanent extension.

Brittle

Fractures before any permanent deformation has taken place.

Strain

Extension divided by its original length.

Tensile Stress

Force exerted per cross-sectional area.

Limit of proportionality

Point beyond which the graph is no longer linear.

Newton's 1st Law

An object moves in a straight line at constant speed unless there is a resultant force acting on it.

Vector

A quantity which has both size and direction

Principle of moments

The sum of the clockwise moments (about a point) is equal to the sum of the anticlockwise moments for a system in equilibrium.

Turning moment

Force x perpendicular distance between the line of action of the force and the pivot.

Couple

Force x perpendicular distance between the lines of action of the forces.

Centre of Mass

Point at which all the mass of the object appears to be concentrated at OR point at which all the objects weight acts

Law of Conservation of Energy

Energy cannot be created or destroyed. It can only be transferred from one form to another.

Relationship between force and momentum

Force is equal to rate of change of momentum

Condition for conservation of momentum

No external forces act on the system.