Mock Physics ALL definitions

angle of incidence

The angle between the direction of travel of an incident wave and the normal at a boundary between two media

angle of reflection

The angle between the direction of travel of a reflected wave and the normal at a boundary between two media

breaking distance

Distance travelled by a vehicle from the time the brakes are applied until the vehicle stops

breaking strength

The stress value at the point of fracture, calculated by dividing the breaking force by the cross-sectional area

brittle

Polymer material that does not show plastic deformation and deforms very little (if at all) under high stress

Brownian motion

The continuous random motion of small particles suspended in a fluid, visible under a microscope

anion

A negatively charged ion, one which is attracted to an anode

anode

A positively charged electrode

cathode

A negatively charged electrode

cation

A positively charged ion, one which is attracted to a cathode

cell

A device that transfers chemical energy into electrical energy

acceleration

The rate of change of velocity, a vector quantity

acceleration of free fall

The rate of change of velocity of an object falling in a gravitational field; symbol g

antiphase

Particles oscillating completely out of step with each other (one reaches its maximum positive displacement as the other reaches its maximum negative displacement) are in antiphase

Archimedes' principle

The upthrust on an object in a fluid is equal to the weight of fluid it displaces

centre of gravity

An imaginary point at which the entire weight of an object appears to act

centre of mass

A point through which any externally applied force produces straight-line motion but no rotation

air resistance

The drag or resistive force experienced by objects moving through air

ammeter

A device used to measure electric current – it must be placed in series and ideally have zero resistance

ampere

The base SI unit of electric current; symbol A, defined as the current flowing in two parallel wires in a vacuum 1 m apart such that there is an attractive force of 2.0×10

amplitude (waves)

The maximum displacement from the equilibrium position (can be positive or negative)

average speed

The rate of change in distance calculated over a complete journey

average velocity

The change in displacement Δs for a journey divided by the time taken Δt, Δs/Δt

charge carrier

A particle with charge that moves through a material to form an electric current – for example, an electron in a metal wire

closed system

An isolated system that has no interaction with its surroundings

coherence

Two waves, or sources, that are coherent have a constant phase difference

diffraction

The phenomenon by which waves spreading through a gap or around an obstacle spread out

diffraction grating

A glass or plastic slide on which as many as 1000 lines to a millimetre are ruled; at a spacing that deflects visible wavelengths of light

diode

A semiconductor component that allows current only in one particular direction

displacement

The distance travelled in a particular direction – it is a vector with magnitude and a direction

displacement (motion)

The distance from the equilibrium position in a particular direction – displacement is a vector, it has a positive or a negative value

drag

The net resistive force exerted by a fluid on an object moving through it

coulomb

The derived SI unit of electrical charge; symbol C; 1 Coulomb of electric charge passes a point in one second when there is an electric current of one ampere. 1 C=1 As

compression

The decrease in length of an object when a compressive force is exerted on it

compression (material)

A region in a longitudinal wave which the medium is denser or has higher pressure than the surrounding medium

compressive deformation

A change in the shape of an object due to a compressive force

compressive force

Two or more forces together that reduce the length or volume of an object

electrolyte

A liquid containing ions that are free to move and so to conduct electricity

electromagnetic spectrum

The full range of frequencies of electromagnetic waves, both gamma rays to radio waves

electromotive force (e.m.f.)

Defined as the energy transferred from chemical to electrical energy per unit charge

critical angle

The angle of incidence at the boundary between two media that will produce an angle of refraction of 90∘

conservation of charge

A conservation law which states that electric charge can neither be created nor destroyed – the total charge in any interaction must be the same before and after the interaction

constant speed

Motion in which the distance travelled per unit time stays the same

constant velocity

Motion in which the change in displacement per unit time stays the same

constructive interference

Superposition of two waves in phase such that the resultant wave has a larger amplitude than the original waves

continuous spectrum

A spectrum in which all visible frequencies or wavelengths are present (a heated solid metal such as a lamp filament will produce this type of spectrum)

ductile

Property of a material that has a large plastic region in a stress-strain graph, so can be drawn into wires

efficiency

The ratio of useful output energy to total input energy when expressed as a percentage

elastic deformation

A reversible change in the shape of an object due to a compressive or tensile force – removal of stress or force will return the object to its original shape and size (no permanent strain)

elastic limit

The value of stress or force beyond which plastic deformation becomes plastic deformation, and the material or object will no longer return to its original shape and size when the stress or force is removed

elastic potential energy

The energy stored in an object due to its elastic deformation

electric current

The rate of flow of charge, symbol I, measured in Amperes, A, normally a flow of electrons in metals or a flow of ions in electrolytes

electron gun

A device that uses a large accelerating potential difference to produce a narrow beam of electrons

electronvolt

A derived unit of energy used for subatomic particles and photons, defined as the energy transferred to an electron when it moves through a potential difference of 1 V; 1 eV is equivalent to 1.6×10−19 J

elementary charge

The electric charge equivalent to the charge on a proton. 1 unit=1.6×10−19 C; symbol e

conventional current

A model used to describe electric current in a circuit – conventional current travels from positive to negative – it is the direction in which positive charges would travel

SI units derived unit

A unit used to represent a derived quantity, such as N for force

destructive interference

Superposition of two waves out of phase so that the waves cancel each other out and the resultant wave has smaller amplitude than the original waves

equilibrium

A body is in equilibrium when the net force and net moment acting on it are zero

hysteresis loop

A loop-shaped plot obtained when, for example, heating and unloading a material produce different deformations

free electron

An electron in a metal that is not bound to an atom and is free to move – effectively, a delocalised electron

free fall

The motion of an object undergoing under gravity with no other force acting on it

free-body diagram

A diagram that represents the forces acting on a single object

frequency

(oscillations) The number of complete oscillations per unit time; unit Hertz (Hz)

frequency (waves)

The number of wavelengths passing a given point per unit time

fundamental frequency

The lowest frequency at which an object1 (e.g. air in a column in a pipe or a string) has a bell (when it has been)

fundamental mode of vibration

A vibration at the fundamental frequency

fundamental particle

A particle that has no internal structure and hence cannot be split into smaller particles

gravitational field strength, g

The gravitational force exerted per unit mass at a point within a gravitational field

gravitational potential

The work done per unit mass to bring an object from infinity to a point in the gravitational field – unit 1 Jkg−1

gravitational potential energy

The capacity for doing work as a result of an object's position in a gravitational field

impulse

The area under a force-time graph – the product of force and the time for which the force acts

in phase

Particles oscillating perfectly in time with each other (reaching their maximum positive displacement at the same time) are in phase

inelastic collision

A collision in which kinetic energy2 is transferred to other forms, e.g. heat

extension

The increase in length of an object when a tensile force is exerted on it

infrared waves

Electromagnetic waves, with wavelengths from 10−3 m to 7×10−7 m

instantaneous speed

The speed at the moment it is measured – speed over an infinitesimal interval of time

intensity (waves)

The radiant power passing through a surface per unit area – unit Wm−2

harmonic

A whole-number multiple of the fundamental frequency

Interference

Superposition of two progressive waves from coherent sources to produce a resultant wave with a displacement equal to the sum of the individual displacements of the two waves

interference pattern

A pattern of constructive and destructive interference formed as waves overlap

force

A push or pull on an object, measured in newtons, N

force constant

A quantity determined by dividing force by extension or compression, for an object obeying Hooke's Law – independent of its proportionality it in Hooke's law, measured in Nm−1

force-extension graph

A graph of force against extension (or compression), with the area under the graph equal to the work done on the material

force-time graph

A graph of net force against time, with the area under the graph equal to the impulse

Hooke's law

The force applied is directly proportional to the extension if the spring unless the limit of proportionality is exceeded

internal resistance

The resistance of a source of e.m.f. (e.g. a cell) due to its construction, which causes a loss in energy/voltage as the charge passes through the source; symbol r; SI unit Ohm, Ω

ion

An atom that has lost or gained electrons and so has a net charge

light-emitting diode

A type of diode that emits light when it conducts electricity

Newton's second law of motion

The rate of change of momentum of an object is directly proportional to the resultant force and takes place in the direction of the force

Newton's third law of motion

When two objects interact, each exert an equal but opposite force on the other during the interaction

I-V characteristic

A description of the relationship between the electric current in a component and the potential difference across it – in most cases this is usually in the form of a simple graph of I against V

limit of proportionality

The value of stress or force beyond which stress is no longer directly proportional to strain

linear momentum

The product of the mass and velocity of a particle, measured in kg m s−1 or Ns

loading (electrical circuits)

Connecting a component or a device across the terminals of a source of e.m.f. or across another component

longitudinal wave

A wave in which the medium is displaced in the same line as the direction of energy transfer – oscillations of the medium particles are parallel to the direction of the wave travel

lost volts

The potential difference across the internal resistor of a source of e.m.f.

microwaves1

Long-wavelength electromagnetic waves, with wavelengths from 10−3 m to 10−1 m

minimum (waves)

The point of least amplitude in an interference pattern, produced by destructive interference

node

For a stationary wave, a point where the amplitude is always zero