Physics 9702 AS Level Notes - Definitions

Measurements
Derived quantities	Physical quantities that are defined in terms of based quantities.
Systematic error	Error in measurement that shifts all readings away from the true value by a constant amount.
Random error	Error in measurement that cause readings to scatter around the true value.
Accuracy	The degree of closeness of measurements to the true value.
Precision	The range of measurements.
Mechanics
Distance	Length of route covered by an object.
Displacement	The distance moved in a particular direction.
Speed	The distance travelled per unit time.
Velocity	The displacement per unit time.
Acceleration	The rate of change of velocity.
Acceleration of Free Fall	The acceleration on an object when the only force acting on it is gravitational pull of the Earth.
Free Fall	The downward motion of an object under the influence of gravitational force only with a constant acceleration. (g=9.81ms^-2)
Newton’s First Law of Motion	An object will maintain uniform velocity or remain stationary unless acted upon by a resultant force. / Momentum of a body remains constant unless acted by a resultant force.
Newton’s Second Law of Motion	The rate of change of momentum is directly proportional to the resultant force.
Newton’s Third Law Motion	Every action there is a reaction of equal magnitude, but in the opposite direction.
Mass	Amount of matter. / Measure of inertia of a body.
Weight	The gravitational force exerted on an object’s mass.
Momentum	The product of mass and velocity.
Impulse	Change of momentum. / The product of a force & the time during which the force is applied.
Force	Rate of change of momentum.
Principle of Conservation of Momentum	The total momentum of a system remains constant before and after a collision, provided that no external force acts upon the system.
Elastic Collision	A collision where the total kinetic energy is constant before and after the collision.
Inelastic Collision	A collision where the total kinetic energy is not conserved.
Upthrust / Buoyant Force	The resultant force on a submerged object due to the difference in pressure.
Centre of Gravity	The point on an object at which the entire weight of the object may be considered to act from.
Moment	The product of force and the perpendicular distance between the pivot and the line of action of the force.
Torque of a Couple	The product of magnitude of any one force and the perpendicular distance between the couple of force.
Principle of Moment	The sum of clockwise moments taken about any point is equal to the sum of anti-clockwise moments taken about the same point when a system is in equilibrium.
Energy	The ability to do work.
Kinetic Energy	The energy possessed by an object due to its motion.
Potential Energy	The energy possessed by an object due to its condition.
Gravitational Potential Energy	The energy stored by an object with mass due to its position in a gravitational field.
Elastic Potential Energy / Strain Energy	The energy possessed by an elastic object when compressed of stretched.
Internal Energy	The total microscopic kinetic energy and potential energy of particles of a material.
Work	The product of force and distance moved in the direction of the force.
Power	Work done per unit time.
Efficiency	The fraction of useful output power/energy from the total power/energy input.
Matter
Density	Mass per unit volume.
Pressure	Force per unit area.
Stress	Force per unit area required to deform a material.
Strain	Extension per unit length.
Young’s Modulus	The ratio of stress to strain.
Elastic Deformation	Deformation of an elastic object when force applied within elastic limit and the object can return to its original shape/length when force is removed.
Plastic Deformation	Deformation of an elastic object when the force applied exceeds the elastic limit and the object can no longer return to its original shape/length when the force is removed.
Elastic limit	Point beyond which an elastic object experiences plastic deformation. (Elastic limit not exceeded if object could return to its original length or shape when force is removed.)
Waves
Displacement of wave	The change in position of an oscillating particle from its equilibrium position in a particular direction.
Amplitude	The magnitude of maximum value of displacement of a particle from its equilibrium position.
Phase Difference	The amount by which one oscillating system leads or lags behind another oscillation.
Period	The time taken to complete one oscillation.
Frequency	The number of complete oscillations per unit time.
Wavelength	Distance between the adjacent wavefronts. / Distance travelled by the wave in one period.
Speed of Wave	The distance travelled per unit time of a crest / at which energy is transferred. (Not the speed at which particles in a wave move.)
Transverse Wave	A wave in which displacement of particles is perpendicular to the direction of wave propagation. (E.g. light waves)
Longitudinal Wave	A wave in which the displacement of particles is parallel to the direction of wave propagation. (E.g. sound wave)
Mechanical Wave	Wave that require a medium to transfer energy.
Electromagnetic Wave	Transverse wave which are formed in combination of electric and magnetic fields oscillating perpendicular to each other.
Stationary Wave	Formed by the overlapping of two waves with equal frequency and wavelength travelling at the same speed but in opposite directions.
Diffraction	Spreading of a wave when it passes through a slit or an edge.
Diffraction Grating	A series of narrow parallel slits design to spread monochromatic light waves over 180 degrees after passing the slits perpendicularly.
Principle of Superposition	When two or more waves of the same type overlap, the resultant displacement of the resultant wave is the sum of displacements of each individual overlapping wave.
Interference	It occurs when two waves overlap and produce a resultant wave with displacement equal to the sum of displacements of each overlapping wave.
Coherence	It is shown when two waves maintain a constant phase difference.
Fringe Separation	The separation between one bright fringe and the next bright fringe.
Doppler Effect	Change in observed frequency when the source of wave moves relative to observer.
Electricity
Electric Field	Region of space where a stationary charge experiences electric force.
Electric Field Strength	Force per unit positive charge of an electric field.
Electric Current	Rate of flow of charge carriers. (When there is no current, electrons move randomly in all directions in a conductor.)
The charge on charge carriers is quantised	Charge exist only in discrete amounts.
Ampere	Coulombs of charge passing through an electric component per second.
Potential Difference	Electrical energy transferred to other forms of energy per unit charge as the charge moves from one point to another in a circuit.
Volt	Joules per column of charge.
Resistivity	The resistivity of a wire of a particular material is its resistance for unit length.
Coulomb	The product of ampere and second.
Ohm’s Law	The current through a metallic conductor is proportional to the potential difference across it provided that its temperature remains constant.
Thermistor (NTC)	A specific type of resistor, in which, as temperature increases, the magnitude of the resistor’s resistance decreases, & vice versa.
Electromotive Force / E.m.f.	Energy transformed from chemical energy to electrical energy per unit charge when a charge flows around a complete circuit.
Potentiometer	When a potential divider arrangement is used to compare e.m.f.s of two sources.
Kirchhoff’s First Law	The algebraic sum of the currents at a junction is zero. (Conservation of Charge.)
Kirchhoff’s Second Law	Around any closed loop in a circuit, the algebraic sum of the e.m.f.s is equal to the algebraic sum of the P.Ds. (Conservation of Energy.)
Nuclear Physics
Mass Number / Nucleon number	The sum of number of protons and neutrons within the nucleus of an atom.
Proton number	Number of protons within the nucleus of an atom.
Isotopes	Atoms of the same element which have the same proton number, but a different nucleon number, due to a change in number of neutrons in their nuclei.
Radioactive Decay	This spontaneous & random process refers to the decay of unstable isotopes of elements until they gain a stable atomic configuration, with the emission of either Alpha, Beta or Gamma radiation.
Electronvolt (eV)	The energy transferred when an electron is accelerated through a potential difference of 1 volt. (1eV=1.60x10^-19J )