Definitions Flashcards
Absorption spectrum
A spectrum of dark lines across the pattern of spectral colours produced when light passes through a gas and the gas absorbs certain frequencies.
Acceleration
The rate of change of velocity, measured in meters per second
Acceleration of free fall
The acceleration of a body falling under gravity
Ammeter
A device used to measure electric current, connected in series with the components
Ampere
SI quantity for electric current
Amplitude
The maximum displacement of a wave from its mean position, measured in meters.
Antinode
A point of maximum amplitude along a stationary wave caused by constructive interference.
Average speed
A measure of the total distance travelled in a certain time.
Braking distance
The distance a vehicle travels while decelerating to a stop.
Brittle
A material that distorts very little and doesn’t exhibit any plastic deformation e.g concrete
Centre of gravity
The point at which the entire weight of an object can be considered to act.
Coherence
Two waves with a constant phase relationship
Conductor
A material with a high number density of conduction electrons and therefore a low resistance.
Conservation of energy
Energy can’t be created or destroyed, just transformed from one form into another or transferred to another place.
Conventional current
A model used to describe the movement of charge in a circuit. from + to -
Coulomb
Unit of electric charge
Couple
Two forces that are equal and opposite to each other but not in the same straight line.
Crumple zone
An area of a vehicle designed to increase the distance over which the vehicle decelerates and so reduce the average force acting
Density
The mass per unit volume, measured in kilograms per cubic meter; a scalar quantity
Diffraction
When a wave spreads out after passing around an obstacle or through a gap.
Displacement
The distance traveled in a particular direction, measured in meters
Drag
The resistive force that acts on a body when it moves through a fluid
Ductile
Materials that have a large plastic region for example, copper.
Elastic deformation
The object will return to its original shape when the deforming force is removed.
Elastic limit
The point at which elastic deformation becomes plastic deformation.
Elastic potential energy
The energy stored in a stretched or compressed object, measured in joules
Electric current
A flow of charge. An SI quantity, measure in Amperes (A); a vector quantity.
Electromagnetic wave
A self-propagating transverse wave that does not require a medium to travel through.
Electron diffraction
The process of diffracting an electron through a gap.
Electron flow
The movement of electrons from - to +.
Electronvolt
One electronvolt is the energy change of an electron when it moves through a potential difference of one volt.
Emission spectrum
A pattern of colours of light, each colour having a specific wavelength.
Energy
The stored ability to do work, measured in joules (J); a scalar quantity.
Extension (x)
The change in length of an object when a force is applied to it, measured in metres (m).
Force (F)
A push or a pull on an object, measured in newtons (N); a vector quantity.
Spring constant (k)
The constant of proportionality in Hooke’s law, measured in newtons per metre (N m-1).
Frequency (f)
The number of oscillations per unit time, measured in hertz
Fundamental frequency
The lowest frequency in a harmonic series where a stationary wave forms.
Fuse
An electrical component designed to heat up, melt and break the circuit when a specified amount of electric current passes through it. Used as a safety device.
Gravitional potential energy
The energy stored in an object by virtue of the object being in a gravitational field.
Harmonics
Whole-number multiples of the fundamental frequency of a stationary wave.
Hooke’s law
Harmonics
Whole-number multiples of the fundamental frequency of a stationary wave.
Hooke’s law
The extension of an elastic body is proportional to the force that causes it.
Infrared
A form of electromagnetic wave with wavelengths between 7.4x10-7 and 10-3 m. Used in remote controls.
Insulator
A material with a small number density of conduction electrons and therefore a very high resistance.
Instantaneous speed
The speed of an object at a given moment in time.
Intensity
The energy incident per square metre of a surface per second, measured in watts per metre squared.
Interference
The addition of two or more waves that results in a new wave pattern.
Joule
Unit of energy (J), e.g. 1200 J. 1 J is the work done when a force of 1 N moves an object 1m in the direction of the force.
Kinetic energy
The work an object can do by virtue of its speed, measured in joules ; a scalar quantity.
Kirchhoff’s first law
The sum of the currents entering any junction is always equal to the sum of the currents leaving the junction.
Kirchhoff’s second law
The sum of the e.m.f.s is equal to the sum of the p.d.s in a closed loop.
LDR
A component that changes its resistance with changes in the light intensity (dark = high resistance, light = low resistance).
Line spectrum
A spectrum produced by a material that contains only certain frequencies due to electron transitions between energy levels.
Longitudinal wave
A wave where the oscillations are parallel to the direction of wave propagation.
Moment of a force
The turning effect due to a single force, measured in newton meters.
Monochromatic light
Light waves with a single frequency (or wavelength).
Newton
Unit of force (N). 1 N is the force which gives a mass of 1 kg an acceleration of 1 m s-2.
Node
A point that always has zero amplitude along a stationary wave caused by destructive interference.
Ohm’s law
The electric current through a conductor is proportional to the potential difference across it, provided physical conditions, such as temperature, remain constant.
Parallel circuit
A type of circuit where the components are connected in two or more branches and therefore provide more than one path for the electric current.
Period
The time taken for one complete pattern of oscillation, measured in seconds (s).
Photoelectric effect
The emission of electrons from the surface of material when electromagnetic radiation is incident on the surface.
Photon
A quantum of light, often described as a particle of light.
Planck’s constant
Constant used in quantum physics; 6.63 × 10-34 J s.
Plane polarised wave
A transverse wave oscillating in only one plane.
Plastic deformation
The object will not return to its original shape when the deforming force is removed, it becomes permanently distorted.
Polarisation
The process of turning an unpolarised wave into a plane polarised wave.
Power
The rate of doing work, measured in watts (W); a scalar quantity.
Pressure
Force per unit area, measured in pascals
Principle of moments
For a body in rotational equilibrium the sum of the clockwise moments equals the sum of the anticlockwise moments.
Progressive wave
A wave that travels from one place to another.
Reflection
When waves rebound from a barrier, changing direction but remaining in the same medium.
Refraction
When waves change direction when they travel from one medium to another due to a difference in the wave speed in each medium.
Resistance
A property of a component that regulates the electric current through it. Measured in ohms (Ω), e.g. 24 Ω.
Resistivity
The ratio of the product of resistance and cross-sectional area of a component and its length.
Scalar
A physical property with magnitude (size) but not direction; for example, speed, distance, pressure, potential difference, etc.
Semiconductor
A material with a lower number density of conduction electrons than a conductor and therefore a higher resistance.
Series circuit
A type of circuit where the components are connected end to end and therefore provide only one path for the electric current.
Spectral line
A line relating to a specific frequency either missing from an absorption spectrum or present in an emission spectrum.
Spectrum
A collection of waves with a range of frequencies, for example, visible spectrum and electromagnetic spectrum.
Speed
The distance travelled per unit time, measured in metres per second , e.g. 12 m s-1; a scalar quantity.
Stationary wave
A wave formed by the interference of two waves travelling in opposite directions.
Stopping distance
Stopping distance = Braking distance + Thinking distance
Strain
The extension per unit length.
Stress
The force per unit cross-sectional area, measured in pascals (Pa).
Superposition
The principle that states that when two or more waves of the same type exist at the same place the resultant wave will be found by adding the displacements of each individual wave.
Tensile force
Usually two equal and opposite forces acting on a wire in order to stretch it. When both forces have the value T, the tensile force is also T, not 2T.
Tensile stress
The tensile force per unit cross-sectional area.
Terminal velocity
The velocity at which an object’s drag equals its accelerating force. Therefore there is no resultant force and zero acceleration.
Thermistor
A component that changes its resistance depending on its temperature. An NTC thermistor’s resistance reduces as the temperature increases.
Thinking distance
The distance travelled from seeing the need to stop to applying the brakes.
Torque
The turning effect due to a couple, measured in newton metres (N m).
Transverse wave
A wave where the oscillations are perpendicular to the direction of wave propagation, e.g. water waves, electromagnetic waves, etc.
Vector
A physical quantity that has both magnitude (size) and direction. For example, velocity, force, acceleration, electric current, etc.
Velocity
The displacement per unit time, measured in metres per second ;a vector quantity.
Volt
Unit of potential difference and e.m.f (V),
Voltmeter
Device used to measure the p.d. across a component. It is connected in parallel across a component.
Watt
Unit of power (W),
Wave
A series of vibrations that transfer energy from one place to another.
Wavelength
The smallest distance between one point on a wave and the identical point on the next wave, measured in metres (m).
Weight
The gravitational force on a body, measured in newtons.
Work
The product of force and the distance moved in the direction of the force, it can also be considered as the energy converted from one form into another, measured in joules (J); a scalar quantity
Work function energy
The minimum energy required to release an electron from a material, measured in joules
Young’s double slit
An experiment to demonstrate the wave nature of light via superposition and interference
Young modulus
The ratio of tensile stress to tensile strain, measured in pascals.
