CIE AS Level Physics Definitions

Comprehensive vocabulary definitions for CIE AS Level Physics covering measurements, dynamics, materials, electricity, waves, and nuclear physics.

Accuracy

Determined by the closeness of the measurements to the true value.

Precision

Determined by the range of measurements or a measure of how close a series of measurements are to one another.

Systematic Error

A constant error in all of the readings that cannot be eliminated by averaging, usually arising from faulty instruments or experimental flaws.

Random Error

A scatter of readings about the true value resulting from uncontrollable factors that can be eliminated by averaging.

Displacement

Distance in a specified direction from a point.

Velocity

Change in displacement per unit time.

Scalar

A quality that only has a magnitude component.

Vector

A quality that has both magnitude and direction components.

Acceleration

Rate of change of velocity.

Newton's First Law

An object will remain at rest or constant velocity unless acted upon by a resultant force.

Newton's Second Law

The resultant force is equal to the rate of change of momentum.

Newton's Third Law

Force on one body is equal in magnitude, but opposite in direction to the other force.

Force

$Rate\ of\ change\ of\ momentum$ or measured in SI units as $\text{kg\,m\,s}^{-2}$ (Newtons).

Mass

Measure of the quantity of matter in a body.

Weight

Force due to the gravitational field.

Conditions for Equilibrium

Resultant force and resultant moment (or torque) in any direction are zero.

Center of Gravity

The point where the entire weight of the body appears to act.

Moment of a Force

Product of force and perpendicular distance from a point.

Principle of Moments

For a body in equilibrium, the sum of clockwise moments about a point is equal to the sum of anticlockwise moments about the same point.

Torque of a Couple

Product of one of the forces of a couple and the perpendicular distance between them.

Work Done

Product of force and distance moved in the direction of the force.

Gravitational Potential Energy

Energy of a mass due to its position in a gravitational field, calculated as $\text{GPE} = mgh$.

Kinetic Energy

Energy of an object due to motion.

Power

Work done per unit time or the rate at which work is done; SI unit is $\text{kg\,m}^2\text{\,s}^{-3}$ (Watt).

Conservation of (Linear) Momentum

Total momentum is constant; sum of momentum before equals sum of momentum after in an isolated system where there is no external force.

Density

Mass per unit volume.

Pressure / Stress

Force per unit area.

Strain

Extension per original length.

Young Modulus

$\text{Stress} / \text{Strain}$.

Elastic Deformation

Object changes shape when force is applied and returns back to the original shape when force is removed.

Hooke's Law

Force is proportional to extension.

Elastic Potential Energy

Ability to do work as a result of the change of shape of an object.

Elastic Limit

Point beyond which the string does not return to the original length after the load is removed.

Plastic Deformation

When the load is removed, the object does not return to original shape.

Ultimate Tensile Stress

The stress at which the material breaks.

Electric Field Strength

Force per unit positive charge.

Coulomb

One ampere second or product of current and time.

Volt

$\text{Joule\,per\,Coulomb}$ or energy transferred per unit charge passing between two points.

Potential Difference

Work done per unit charge or energy transferred from electrical to thermal.

Electromotive Force (EMF)

Energy transferred from chemical to electrical.

Internal Resistance

Resistance of the cell causing a loss of voltage or energy loss in the cell.

Kirchhoff's First Law

Sum of currents entering a junction is equal to the sum of currents out of a junction (Conservation of Charge).

Kirchhoff's Second Law

Sum of electromotive force is equal to the sum of potential difference around any closed network (Conservation of Energy).

Wavelength

Distance between two adjacent wave fronts or two adjacent points in phase.

Amplitude

Maximum displacement of a particle from the position of equilibrium.

Frequency

Number of vibrations or oscillations per unit time.

Longitudinal Waves

Vibration of particles is parallel to the direction of propagation of energy.

Transverse Waves

Vibration of particles is perpendicular to the direction of propagation of energy.

Doppler Effect

Change in observed frequency when source moves relative to the observer.

Superposition

When two waves meet, the resultant displacement is the sum of the individual displacements of each wave.

Diffraction

Spreading of a wave when it passes through a gap or slit.

Coherent Waves

Waves with a constant phase difference.

Stationary Waves

Formed when two waves of the same frequency and wavelength overlap while travelling in opposite directions; energy is stored, not transferred.

Node

Position of zero amplitude on a stationary wave.

Antinode

Position of maximum amplitude on a stationary wave.

Alpha Particle

Helium nucleus with high ionizing power and a range of a few millimeters (sheet of thin paper); positively charged/deflected in fields.

Beta Particle

Electron ($\beta^-$) or Positron ($\beta^+$) with lower ionizing power than Alpha; range of several meters.

Isotopes

Atoms with the same proton number but different number of neutrons (or nucleon number).

Quark Charges

Up quark = $+2/3$, Down quark = $-1/3$.

Baryons

Hadrons made up of 3 quarks, such as protons ($uud$) and neutrons ($udd$).

Mesons

Hadrons made up of 2 quarks.

Leptons

Particles including electrons, neutrinos ($\nu$), and muons.

Red Shift

An observed increase in the wavelength of light from distant galaxies.