CIE AS Level Physics - Definitions

Accuracy

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

Precision

Determined by the range of measurements.

Systematic Error

A constant error in all of the readings and cannot be eliminated by averaging. Usually an error in the instrument.

Random Error

A scatter of readings about the true value that can be eliminated by averaging. Usually an error by the observer.

Displacement

Distance in a specified direction from a point.

Velocity

Change in displacement per unit time.

Scalar

Only has magnitude component.

Vector

Has magnitude and direction component.

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.

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 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.

Kinetic Energy

Energy of an object due to motion.

Power

Work done per unit time.

Conservation of (Linear) Momentum

Total momentum is constant; Sum of momentum before is equal to the sum of momentum after where there is no external force.

Density

Mass per unit volume.

Pressure / Stress

Force per unit area.

Strain

Extension per original length.

Young Modulus

Stress by Strain

Elastic Deformation / Extends Elastically

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

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

Region of space where a charge experiences a force.

Electric Field Strength

Force per unit positive charge.

Field Line

Path in which positive charge will move.

Charge

Product of current and time.

Coulomb

One ampere second or product of current and time.

Volt

Joule per Coulomb

Electric Current

Flow of charge carriers

Potential Difference

Work done per unit charge or Energy transferred from electrical to thermal

Electromotive Force

Energy transferred from chemical to electrical.

Resistance

Potential difference per unit current.

Internal Resistance

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

Ohm

Volt per unit Amperes.

I = nAve

n = Number density of free electrons

A = Cross-sectional area

v = Drift velocity

e = Charge of an electron

Kirchhoff's First Law

Sum of currents entering a junction is equal to the sum of currents out of a junction.

Kirchhoff's Second Law

Sum of electromotive force is equal to the sum of potential difference.

Wavelength of Progressive Waves

Distance between two adjacent wave fronts.

Displacement of Waves

Distance from position of equilibrium.

Amplitude

Maximum displacement of a particle.

Period

Time taken to complete one cycle or oscillation of a vibrating object.

Frequency

Number of vibrations per unit time.

Energy Transfer in Progressive Waves

Energy is transferred.

Phase of two adjacent particles in Progressive Waves

Particles are out of Phase.

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.

Interference

Sum of the displacements of the overlapping waves.

Coherent Waves

Constant phase difference.

Conditions to Form Stationary Waves

When two waves, of the same frequency and wavelength, overlap while travelling in opposite directions.

Energy Transfer in Stationary Waves

Energy is not transferred.

Phase of two adjacent particles in Stationary Waves

Particles are in phase.

Node

Position of zero amplitude

Antinodes

Position of maximum amplitude.

Radioactive Decay of a Nucleus

Nucleus emits alpha or beta particles and/or gamma rays.

Alpha Particle

Helium nucleus, higher ionizing power, slower than Beta.

Properties of Alpha Particle

Range is a sheet of thin paper, causes dense ionization in air, positively charged, deflected in magnetic or electric fields.

Beta Particle

Electron, lower ionizing power, faster speed.

Isotope

Atoms with the same proton number but different number of neutrons.