AS Level Physics 9702: Physical quantities, units and measurements

A set of vocabulary-style flashcards covering key terms from the AS Level Physics 9702 notes on quantities, units, measurements, dynamics, waves, and modern physics.

Systematic error

An error that causes readings to be consistently larger or smaller than the true value by a constant amount (or vary by a constant offset).

Random error

An error that causes readings to scatter around the true value and is not constant.

Precision

The smallest division on a measuring instrument or the fineness of a set of measurements.

Accuracy

How close a measurement is to the true value.

Scalar

A physical quantity with magnitude only, no direction.

Vector

A physical quantity with both magnitude and direction.

Displacement

Distance from a reference point in a specified direction; a vector quantity; also describes the change in position of a point on a wave.

Speed

Distance travelled per unit time.

Velocity

Rate of change of displacement; speed with a direction.

Acceleration

Rate of change of velocity.

Mass

Property of an object that resists changes in motion (amount of matter).

Linear Momentum

The product of an object’s mass and its velocity.

Force

The push or pull that causes a change in motion; rate of change of momentum.

Newton

The unit of force; 1 N = 1 kg m s−2.

Newton’s 1st law

An object at rest or moving with constant velocity stays so unless acted on by a resultant force.

Newton’s 2nd law

Resultant force equals the rate of change of momentum (F = dp/dt); for constant mass, acceleration is proportional to force.

Newton’s 3rd law

For every action, there is an equal and opposite reaction.

Conservation of linear momentum

In a closed system, total momentum in any specified direction remains constant.

Perfectly Elastic collision

A collision in which kinetic energy (and momentum) is conserved.

Inelastic collision

A collision where kinetic energy is not conserved; energy may transfer to heat or deformation.

Centre of gravity

The point at which the entire weight of an object appears to act.

Moment

The moment of a force about a point = force × perpendicular distance to the point.

Principle of moments

For rotational equilibrium, sum of clockwise moments equals sum of anticlockwise moments about the same point.

Conditions of equilibrium

(1) Resultant force in any direction is zero; (2) resultant torque about any point is zero.

Density

Mass per unit volume.

Pressure

Force acting normally per unit area of a surface.

Elastic limit

Stress beyond which an object will not return to its original dimensions when the force is removed.

Limit of proportionality

Stress beyond which force and extension are no longer proportional.

Hooke’s law

Extension or compression is proportional to the applied force, provided the limit of proportionality is not exceeded.

Spring constant

The ratio of force to extension for a spring or wire.

Stress

Force per unit cross-sectional area.

Strain

Extension per unit original length produced by tensile or compressive forces.

Young’s modulus

Ratio of stress to strain for a material (within the limit of proportionality).

Strain energy / elastic potential energy

Energy stored in an object due to extension/compression or change of shape.

Work

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

Energy

A conserved quantity; the ability to do work or be transferred when forces act.

Power

Rate at which energy is transferred or work is done.

Efficiency

Ratio of useful output energy to total input energy, expressed as a percentage.

Gravitational potential energy

Energy due to height in a gravitational field.

Kinetic energy

Energy due to an object’s motion.

Conservation of energy

In a closed system, total energy in all forms remains unchanged during any change.

Transverse wave

A wave in which particle displacement is perpendicular to the direction of energy propagation.

Longitudinal wave

A wave in which particle displacement is parallel to the direction of energy propagation.

Progressive wave

A wave that carries energy from one place to another without transferring the medium.

Stationary/standing wave

A wave pattern from two progressive waves of the same frequency traveling in opposite directions; has nodes and antinodes; energy is trapped.

Displacement (waves)

Distance from the equilibrium position of a particle/point on a wave.

Amplitude

Maximum displacement of a particle or point on a wave.

Frequency

Number of oscillations per unit time (or number of wavefronts passing a point per unit time).

Period

Time for one oscillation or cycle; interval between successive wavefronts in phase.

Wavelength

Distance moved by a wavefront during one cycle; distance between adjacent points in phase.

Doppler effect

Change in observed frequency or wavelength when the source or observer is moving relative to the other.

Unpolarised wave

A transverse wave with vibrations in all planes.

Plane polarised wave

A transverse wave with vibrations in a single plane.

Malus’s law

I = I0 cos^2(θ); intensity after passing through a polarisation filter depends on the angle θ.

Principle of superposition

When two waves meet, the resultant displacement is the sum of their displacements.

Interference

The combination (sum) of displacements from overlapping waves.

Diffraction

The spreading of a wave as it passes through a gap or around an edge.

Coherence

Two sources are coherent if they emit waves with a constant phase difference.

Conditions for stationary wave formation

Two waves traveling at the same speed in opposite directions overlap and have the same frequency/wavelength.

Nodes

Points on a stationary wave with zero amplitude.

Antinodes

Points on a stationary wave with maximum amplitude.

Current

Rate of flow of electric charge.

Ampere

Unit of current; 1 A = 1 C s−1.

Coulomb

Unit of electric charge; 1 C = 1 A·s.

Number density of charge carriers

Number of charge carriers per unit volume in a material.

Mean drift velocity

Average velocity of charge carriers when a current flows.

Electromotive force (emf)

Work done or energy transformed per unit charge when moving around a complete circuit.

Potential difference (p.d)

Work done or energy transformed per unit charge.

Volt

Unit of potential difference; 1 V = 1 J C−1.

Resistance

Ratio of potential difference to current.

Ohm

Unit of resistance; 1 Ω = 1 V A−1.

Ohm’s law

Current is directly proportional to potential difference at constant temperature.

Kirchhoff’s 1st law

Sum of currents entering a junction equals the sum leaving; conservation of charge.

Kirchhoff’s 2nd law

Sum of emfs around a closed loop equals the sum of the p.d.s; conservation of energy.

Isotopes

Nuclei of the same element with different numbers of neutrons but the same number of protons.

Antimatter

An antiparticle has the same mass as its matter counterpart but opposite charge; they annihilate and mass converts to energy.

Fundamental particles

Particles not made up of any smaller constituents (elementary particles).

Hadrons

Particles affected by the strong nuclear force.

Baryons

Hadrons made up of three quarks.

Mesons

Hadrons made of a quark and an antiquark.

Leptons

Particles not affected by the strong nuclear force.