Physics AS Level (Chp 1 -15) Keywords

PHYSICS KEYWORD LIST:

Average Speed: The total distance travelled by an object divided by the total time taken.

Instantaneous Speed: The speed of an object measured over a very short time.

Displacement: The distance travelled in a particular direction; it is a vector quantity.

Vector Quantity: A quantity with both magnitude and direction.

Scalar Quantity: A quantity with magnitude only.

Velocity: An object’s speed in a particular direction or the rate of change of its displacement; it is a vector quantity.

Vector Triangle: A triangle drawn to determine the resultant of 2 forces.

Resultant Vector: The single vector formed by adding together 2 or more vectors.

Uniform Acceleration: When the change in velocity of an object is the same at the same time.

Non-Uniform Acceleration: When the velocity of an object changes by different amounts in the same period.

Tangent: A straight line that touches a curve but does not cross it at a point.

Free Fall: When an object accelerates due to gravity in the absence of any other forces, such as air resistance.

Component: The effect of a vector along a particular direction.

Weight: Force on an object caused by a gravitational field acting on its mass.

Friction: Name for a resistive force when 2 surfaces are in contact and tending to slide over one another.

Centre of Gravity: The Point where the entire weight of an object appears to act.

Uniform motion: Natural state of motion of an object-uniform velocity, constant speed and direction.

Resultant Force: A single force that has the same effect as all of the forces acting on an object.

Terminal Velocity: Maximum velocity reached by an object falling under gravity or accelerated by a constant force.

Resistive Force: Backwards force in the opposite direction to movement caused by friction or some other viscous force.

Drag: Force that resists the movement of a body through a fluid.

Contact Force: Force at right angles to a surface when 2 objects are in contact.

Upthrust: Force upwards in a liquid or gas caused by the pressure in the gas or liquid.

Homogeneous: Equations with the same base units on each side are homogeneous.

Base Units: Defined units of the SI system from which all units are derived.

Derived Units: Units that are combinations of the base units of the SI system.

Newton: 1 N is the force that will give a 1 kg mass an acceleration of 1 m/s^2 in the direction of the force.

Resultant Force: A single force that has the same effect as all of the forces acting on an object.

Triangle of forces: A closed triangle drawn for an object in equilibrium. The sides of the triangle represent the forces in both magnitude and direction.

Equilibrium: An object in equilibrium is either at rest or travelling with a constant velocity because the resultant force on it is zero.

Components: Magnitudes of a vector quantity in 2 perpendicular directions.

Resolving: Splitting a vector into 2 vectors at right angles.

Free-body force diagram: Diagram showing all the forces acting on an object.

Moment of a force: The moment of a force about a point is the product of the force and the perpendicular distance from the line of action of the force to the point.

Couple: A pair of equal and opposite forces that act on an object at different points and produce rotation only.

Torque (of a couple): Product of one of the forces and the perpendicular distance between the forces.

Energy: Calculated quantity that is conserved during any change; that which is transferred when a force does work.

Gravitational Potential Energy (GPE): Energy a body has due to its position in a gravitational field.

Closed system: A system of interacting objects in which there are no external forces.

Perfectly Elastic: The total kinetic energy of all the bodies remains constant.

Inelastic: Kinetic energy is not conserved; some is transferred to other forms, such as heat.

Compressive: Force that squeezes and shortens an object.

Tensile: Associated with tension or pulling; ie, a tensile force.

Extension: Increase in the length of a material from its original length.

Spring Constant: Force per unit extension for a spring; unit is N/m.

Elastic Deformation: An object that returns to its initial length when the force is removed has deformed elastically.

Plastic Deformation: An object that does not return to its initial length when the force is removed is deformed permanently.

Limit of Proportionality: The point beyond which extension is no longer proportional to the force.

Elastic Limit: Value of stress beyond which an object will not return to its original dimensions.

Elastic Potential Energy (Strain Energy): Energy stored in a body due to a change in its shape.

Work done: Product of the force and the distance moved in the direction of the force; the area under a force-extension graph.

Charge carrier: A charged particle that contributes to an electric current; these may be electrons, protons, or ions.

Quantised: Quantity is said to be quantised when it has a definite minimum magnitude and always comes in multiples of that magnitude.

Current: Rate of flow of electric charge past a point.

Ampere: SI unit of electric current.

Coulomb: 1C is the charge that flows past a point in a circuit in a time of 1s when the current is 1A.

Elementary Charge: e = 1.6 x 10^-19 C.

Number Density: Number of charge carriers, such as free electrons, per unit volume in a material.

Mean Drift Velocity: Average speed of a collection of charged particles when there is a current in a conductor.

Homogeneous: For an equation to be valid, the units must be homogeneous, which means that units, when reduced to the base units, are the same for each term in the equation.

Ohm: Resistance of a component when a potential difference of 1V drives a current of 1A through it.

Conservation of charge: Electric charge can neither be created nor destroyed.

I-V Characteristic: Graph of current against voltage for a particular component of an electrical circuit.

Resistor: An electrical component whose resistance in a circuit remains constant and is independent of current or potential difference.

NTC Thermistor: A device whose resistance decreases rapidly when the temperature increases.

Threshold Voltage: Minimum forward potential difference across a diode at which it starts to conduct.

Light-Dependent Resistor (LDR): A component whose resistance decreases with light intensity.

Delocalised Electron: An electron that is not attached to a specific ion, but is free to move throughout the crystal lattice.

Resistivity: Property of a material; it measures its electrical resistance, defined by p = (RA)/L. Unit: Ω m

Internal Resistance: Internal resistance of a source of EMF is the resistance inherent in the source itself; some energy is transferred into other forms as work is done in driving charge through the source itself.

Terminal p.d: Potential difference across the terminals of a source, and is dependent on the current that is taken from the source.

Potential Divider: Circuit that splits the potential difference (V) from a source into 2 parts, so that the p.d. across one section is V₁ and the p.d. across the other is V₂, where V₁ + V₂ = V.

Potentiometer: A device used to compare potential differences.

Sensor or transducer: An electronic component with a property that changes when a physical quantity, such as temperature or light intensity, alters.

Galvanometer: An instrument used to measure or detect small electric currents. It is often not calibrated. By adding resistors in series or parallel with it, and with suitable calibration, it can act as a voltmeter or an ammeter, respectively.

Null Method: Experimental technique where a zero reading is sought. The word ‘null’ comes from the Latin ‘nullus’, meaning ‘not any more’ or ‘nothing’.

Wave: A periodic disturbance travelling through space, characterised by a vibrating medium.

Progressive Wave: A wave that carries energy from 1 place to another.

Displacement: Distance of a point on the wave from its undisturbed or equilibrium position.

Amplitude: Maximum displacement of a wave.

Wavelength: Distance between 2 adjacent points on a wave oscillating in step with each other.

Period: Time taken for 1 complete oscillation of a point in a wave.

Frequency: Number of oscillations per unit time of a point in a wave.

Longitudinal Wave: A wave in which the particles of the medium oscillate along the direction in which the wave travels.

Transverse Wave: A wave in which the particles of the medium oscillate at right angles to the direction in which the wave travels.

Compression: Point in a sound wave at which the air pressure is at maximum.

Rarefaction: Region in a sound wave where the air pressure is less than its mean value.

Phase Difference: Fraction of a cycle between 2 oscillating particles, expressed in either degrees or radians.

Intensity: Intensity is the rate of energy transmitted (power) per unit area at right angles to the wave velocity.

Doppler Effect: Change in frequency or wavelength of a wave observed when the source of the wave is moving towards or away from the observer (or the observer is moving relative to the source).

Electromagnetic Spectrum: A family of waves that travel through a vacuum at a speed of 3 x 10⁸ m/s.

Magnetic Field: A force field in which a magnet, a wire carrying a current, or a moving charge experiences a force.

Electromagnetic Wave: Transverse waves travel through space as electric and magnetic field vibrations.

Electric Field: A force field in which an electrically charged particle experiences a force.

Plane Polarised: Describes a transverse wave with oscillation in just 1 plane. Only transverse waves can be polarised.

Diffraction: Spreading of a wave when it passes through a gap or past the edge of an object.

Interference: Superposition of 2 or more waves from coherent sources.

Constructive Interference: When 2 waves reinforce to give increased amplitude at a point in space.

Destructive Interference: When 2 waves cancel to give reduced (or zero) amplitude at a point in space.

Coherent Sources: 2 sources with exactly the same frequency, and have 0 or a constant phase difference.

Path Difference: Extra distance travelled by one of the waves compared with the other. Path difference is often given in terms of the wavelength of the waves.

Interference Maxima: Regions where light waves from 2 slits arrive in phase with each other; in other words, there is constructive interference.

Coherence: 2 waves emitted from 2 sources that have a constant phase difference. The sources emitting such waves are referred to as coherent sources.

Dispersion: Splitting of light into its component wavelengths.

Stationary wave/standing wave: A stable wave pattern produced from the superposition of 2 progressive waves of the same frequency and travelling in opposite directions. A stationary wave has nodes and antinodes.

Node: Point on a stationary wave with 0 amplitude.

Antinode: Point on a stationary wave with maximum amplitude.

Resonance: When a system oscillates with maximum amplitude by absorbing energy from a vibrating source. Resonance in an air column of a tube is demonstrated by the loud sound from the tube.

Plum Pudding Model of the atom: A model that pictured the atom as a positive sphere of pudding with small negatively charged plums embedded in it.

Nuclear Model of the atom: A model that pictures the atom having a tiny positively charged nucleus that carries almost all of the atom's mass, surrounded by the much smaller, negatively charged electrons.

Nucleus (of an atom): Tiny, but very dense, positively charged centre of an atom.

Nucleon: A general term to describe protons and neutrons.

Nucleon number: Total number of neutrons and protons in the nucleus of an atom.

Neutron number: Number of neutrons in the nucleus of an atom.

Proton number: Number of protons in the nucleus of an atom.

Nuclide: Specific combinations of protons and neutrons in a nucleus.

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

Ion: An atom that has lost or gained one or more electrons, so that it is electrically charged.

Strong nuclear force: Fundamental force that acts between particles such as protons and neutrons, but which does not affect particles like electrons.

Positron: Antiparticle of the electron. It has the same mass as the electron but has a charge +e.

Beta minus decay: Emission of an electron as a neutron decays into a proton.’

Beta plus decay: Emission of a positron as a proton decays into a neutron.

Antimatter: Material made up of antiparticles of the corresponding particles of ordinary matter.

Electron neutrino: A particle that is emitted with beta plus decay with virtually no rest mass and no charge.

Electron antineutrino: Antiparticle that is given off with beta minus decay with virtually no rest mass and no charge. (-ve)

Leptons: Subatomic particles that are not affected by the strong nuclear force and are believed to be fundamental.

Hadrons: Subatomic particles made up of quarks that are affected by the strong nuclear force.

Quarks: Fundamental particles that make up hadrons.

Baryon: Hadron made up of 3 quarks.

Meson: A hadron is made up of a quark and an antiquark.