Definitions

A combination of markscheme answers and textbook definitions.

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AS Level Physics Terms & Concepts

Here's a useful set of flashcards for AS revision:

• https://quizlet.com/356145378/as-level-physics-definitions-cie-flash-cards/
• https://quizlet.com/527383170/cie-as-level-physics-definitions-flash-cards/

Lvl	Ch	Term	Definition
AS	1	Derived Units	Some combination of the base units. The base units may be multiplied together or divided by one another, but never added or subtracted.
AS	1	Homogeneous Units	When each term has the same base units, the equation is said to be homogeneous or ‘balanced’.
AS	1	Scalar	A quantity that has magnitude/size
AS	1	Vector	A quantity that has magnitude/size and direction
AS	1	Accuracy	How close a reading is to its true value. When readings are accurate, the peak / average value moves towards the true value
AS	1	Precision	Smallest change in value that can be measured by an instrument. OR Spread of values / measurements (scatter between each data is relatively small/ lines are closer together / sharper peak)
AS	1	Random errors	Readings have positive and negative values around the peak value / values are scattered / wide range. To reduce errors, take several readings to get an average value.
AS	1	Systematic Error	The average / peak is not the true value / the readings are not centred around the true value. Look/check for zero error to avoid systematic error.
AS	1	Uncertainty	The range of value within which a measurement is likely to be in.
AS	2	Acceleration (vector)	Rate of change of velocity.
AS	2	Displacement (vector)	is the straight line distance between start and finish points (in that direction) / minimum distance
AS	2	Distance (scalar)	is the actual path travelled
AS	2	Free Fall	The downward motion of an object under the influence of force of gravity with a constant acceleration (g = 9.81 ms-2).
AS	2	Projectile motion	Objects acted upon by a force with vector at perpendicular to its horizontal velocity. Asume zero frictional forces. Tracjectory of the object will result in a parabola.
AS	2	Speed (scalar)	Distance travelled per unit time taken
AS	2	Terminal velocity	Constant speed of object when resultant force is zero due to large air resistance.
AS	2	Velocity (vector)	Rate of change of displacement
AS	3	Conservation Of Momentum	Total momentum of (an isolated) system (of interacting bodies) remains constant, provided there are no resultant external forces (e.g. friction)
AS	3	Elastic Collisions	Total momentum and total Kinetic Energy of a system is conserved. Relative speed of approach is equal to the relative speed of separation
AS	3	Force	Rate of change of momentum
AS	3	Force	It is defined as the rate of change of momentum of a body
AS	3	Impulse	It is the product of a force & the time during which the force is applied.
AS	3	Inelastic Collisions	Total momentum of a system is conserved, but the total Kinetic Energy is not conserved. Speed before impact is not equal to speed
AS	3	Linear Momentum	Product of an object's mass & velocity, with its direction always being the same as the direction of velocity.
AS	3	Mass	It is a measure of inertia of a body or the property of a body that resists change in motion
AS	3	Newton’s 1st Law	A body remains at rest or constant velocity unless acted on by a resultant (external) force
AS	3	Newton’s 2nd Law	The (resultant) force is proportional to the rate of change of momentum
AS	3	Newton’s 3rd Law	If one body exerts a force on another, it will experience a force by the other body, which is equal in magnitude & opposite in direction. Both forces are the of the same kind.
AS	3	Weight	Weight is the force due to the gravitational field
AS	4	Centre Of Gravity	The point on an object at which the entire weight of the body seemingly acts. It is the point at which the Earth actually applies the pull of gravity.
AS	4	Density	Amount of mass per unit volume of a substance.
AS	4	Equilibrium	Net / resultant force and moment is zero (OR sum of clockwise moments = sum of anticlockwise moments). If the triangle of forces is ‘closed’ then there is no resultant force and the object is in equilibrium.
AS	4	Moment / Torque	Product of the force and the perpendicular distance to the pivot
AS	4	Pressure	The perpendicular/normal force applied per unit area
AS	4	Principle Of Moments	The sum of the clockwise moments about a point equals the sum of the anticlockwise moments (about the same point)
AS	4	Torque Of A Couple	Product of one of the forces and perpendicular distance between forces. (The turning effect caused by two equal & opposite forces when their line of actions are different.)
AS	4	Upthrust	It is the resultant force on a submerged object due to pressure difference between the higher pressure at the bottom of the object and the lower pressure at the top of the object immersed in a fluid.
AS	5	Energy	It is the stored ability to do work.
AS	5	Work Done	Product of a force & the distance moved in the direction of the force.
AS	5	Gravitational Potential Energy	Energy stored due to height/position of mass
AS	5	Internal Energy	It is the total of the microscopic Kinetic & Potential energies of particles of a material.
AS	5	Kinetic Energy	Energy of an object due to its motion.
AS	5	Potential Energy	Energy stored by an object to do work
AS	5	Elastic Potential Energy	Energy stored due to deformation or change in shape of an object
AS	5	Electric potential energy	Potential energy (stored) when charge moved due to work done in electric field
AS	5	Power	Rate of work done
AS	5	Efficiency	The fraction of the useful power output obtained from the total power input.
AS	6	Brittle Materials	Materials which do not undergo plastic deformation. Force proportional to extension until it breaks
AS	6	Ductile Materials	Materials which undergo plastic deformation after a considerable elastic deformation. Initially force proportional to extension then a large extension for small change in force
AS	6	Elastic Deformation	Object returns to its original length (zero extension) when load is removed
AS	6	Force-Extension Graph	The area under such a graph is the work done in stretching a material. For the straight-line portion of the graph, it is a measure of the elastic potential energy stored by the material, provided that the graph for decreasing loads is the same as that for increasing loads. It is also known as strain energy.
AS	6	Hooke's Law	Force/load is proportional to extension/compression if proportionality limit is not exceeded.
AS	6	Necking	When a sufficiently large force is applied, localized narrowing occurs at weak points, & the wire eventually breaks at one of these points.
AS	6	Plastic Deformation	Wire/body object does not return to its original shape / length when load is removed
AS	6	Polymeric Materials	Materials which can undergo great strain, & deform to a very great degree. E.g. rubber, glass, cement
AS	6	Strain	Extension over original length (ratio). Stress is the cause & strain is the effect.
AS	6	Stress	It is the force per unit cross-section area required to stretch a material.
AS	6	Ultimate Tensile Strength	The maximum force / original cross-sectional area the wire is able to support before it breaks
AS	6	Ultimate Tensile Stress	The maximum value of stress that an object can sustain before it breaks.
AS	6	Young’s Modulus	Ratio of stress to strain.
AS	7	Progressive wave	The transfer or propagation of energy as a result of oscillations / vibrations
AS	7	Transverse Waves	A wave in which displacement of particles is perpendicular to the direction of wave propagation, resulting in crests & troughs. Transverse waves have vibrations that are perpendicular / normal to the direction of energy travel
AS	7	Longitudinal Waves	A wave in which displacement of particles is parallel to the direction of wave propagation. Longitudinal waves have vibrations that are parallel to the direction of energy travel
AS	7	Wavelength	Distance moved by wave energy / wavefront during one cycle of the source or minimum distance between two points with the same phase or between adjacent crests or troughs.
AS	7	Frequency (Hz)	Number of oscillations per unit time (not per second)
AS	7	Period	The time taken to complete one oscillation/cycle. Or time between adjacent wavefonts.
AS	7	Amplitude	Maximum displacement of a particle in the wave
AS	7	Displacement	Distance (of point on wave) from rest / equilibrium position
AS	7	Phase Difference	The difference in the relative positions of the crests or troughs of two waves of the same frequency expressed in radians or degrees.
AS	7	(Wave) Intensity	The intensity of a wave is the energy passing through unit area per unit time.
AS	7	(Wave) Speed	Speed at which energy is transferred / speed of wavefront. It is NOT the speed with which particles in the wave move.
AS	7	Doppler Effect	Change in observed frequency when source moves relative to the observer
AS	7	Electromagnetic Waves	electromagnetic waves (a transverse wave) can travel through a vacuum / free space. The displacement in the case of electromagnetic waves is a variation in the electric & magnetic fields perpendicular to each other.
AS	7	Polarisation	Oscillations or vibrations are in one direction, perpendicular to direction of propagation.
AS	8	Transfer of Energy	The transfer of energy is due to a progressive wave, NOT a standing/stationary wave.
AS	8	Coherence	Two waves with a constant phase difference are said to be coherent.
AS	8	Principle of Superposition	When two waves of the with similar frequency &amp meet/overlap, the resultant displacement is the sum of the individual displacement of each wave.
AS	8	Node	Position along wave with no motion / zero amplitude
AS	8	Antinode	Position along wave with maximum amplitude.
AS	8	Constructive Interference	Two waves' path difference is either λ or nλ, OR phase difference is 360°or n ×360° or n2π
AS	8	Destructive Interference	Two waves' path difference is either λ/2 or (n+ ½) λ OR phase difference is odd multiple of either 180° or π rad
AS	8	Stationary Waves	Two waves of same frequency/wavelength travelling (along the same line) in opposite directions overlap/meet. The resultant displacement is the sum of displacements of each wave / produces nodes and antinodes
AS	8	Stationary Wave Properties	Does not transfer energy (no energy transfer). The amplitude of standing wave varies along its length/nodes and antinodes.Neighboring points (in inter-nodal loop) vibrate in phase
AS	8	Fringe Width/Separation	The separation between one bright fringe & the next bright fringe.
AS	8	Interference	When two waves superpose/overlap, the resultant displacement is the sum of individual displacements of overlapping waves, forming alternating maxima and minima.
AS	8	Diffraction	When a wave (front) passes by/incident on an edge/slit, the wave spreads into the geometrical shadow
AS	8	Diffraction Grating	When waves pass through the gaps / slits in the grating, the wave bends/spreads (into the geometrical shadow)
AS	8	Refraction	The change in direction of a wave due to change in speed.
AS	9	Ampere	If a charge of 1 Coulomb passes through an electrical component per second, then the current maintained is 1 Ampere
AS	9	Charge	Charge = current x time
AS	9	Coulomb	The SI unit of electrical charge. A charge of 1C passes a point when a current of 1A flows for 1s.
AS	9	Electric Current	It is the amount of charge flowing pass a point per unit time.Or rate of flow of charged particles.
AS	9	Ohm	volt/ampere
AS	9	Ohm’s Law	The current through a metallic conductor is proportional to the P.D across it provided that its temperature remains constant.
AS	9	Potential Difference	Energy converted from electrical to other forms of energy per unit charge that passes through it.
AS	9	Quantised	Charge only exists in discrete amounts. Charge on carriers is quantised.
AS	9	Resistance	The ratio of P.D over the current for an electrical component
AS	9	Resistivity	The resistivity of a wire of a particular material is its resistance for unit length.
AS	9	Thermistor	A specific type of resistor, in which, as temperature increases, the magnitude of the resistor’s resistance decreases, & vice versa.
AS	9	Volt	P.D between two points in a circuit in which 1J of energy is converted when 1C of charge passes from one point to the other.
AS	10	E.m.f & P.D	While e.m.f refers to the amount of energy converted into electrical energy per unit charge supplied, P.D refers to the amount of electrical energy converted into other forms of energy per unit charge supplied. The e.m.f of a source is equal to the potential difference across its terminals as the current approaches zero.
AS	10	Electromotive Force	Energy converted from chemical into electrical energy per unit charge.
AS	10	Internal Resistance	(resistance of the cell) causing loss of voltage or energy loss in cell
AS	10	Kirchhoff’s 1st Law	The sum of currents into a junction = sum of currents out of junction, Because charge cannot be created or destroyed (conservation of charge).
AS	10	Kirchhoff’s 2nd Law	Sum of e.m.f.’s = sum of p.d.’s around a loop/circuit. Because any gains in electrical energy of a charge must be balanced by corresponding losses of energy (conservation of energy).
AS	10	Law of Conservation of Charge	Kirchhoff’s First & Second Laws are in correspondence & actually are an appreciation of the Law of Conservation of Charge & the Law of Conservation of Energy respectively.
	10	Output Power (Circuit)	A battery delivers the maximum power to a circuit when the load resistance of the circuit is equal to the internal resistance of the battery. When load resistance is zero, power dissipated by load is zero because P=I^2R. When load resistance is very large, power dissipated gets very small as the current through the load is reduced significantly.
AS	10	Potentiometer	When a potential divider arrangement is used to compare e.m.fs of two sources, it is known a potentiometer.
AS	11	Alpha particle	Either helium nucleus OR particle containing two protons and two neutrons with mass 4u. Radiation can be deflected in electric/magnetic fields, and absorbed by thin paper or few cm of air. Radiation is highly ionizing.
	11	Baryon	A type of hadron particle that is made up of three quarks (e.g. proton and neutron).
AS	11	Beta Particle	Produced due to weak nuclear force/interaction. β-particles are fast moving electrons with a range of speeds up to 0.99c. This radiation can be deflected by electric and magnetic fields or negatively charged, and absorbed by few (1 – 4) mm of aluminum. 0.5 to 2m for range in air.
AS	11	Gamma Radiation	γ- radiation is part of the electromagnetic spectrum with wavelengths between 10^(-11) m and 10^(-13) m.
	11	Hadron	Class of heavy particles made up of quarks held together by strong nuclear force. Hadron is not a fundamental particle.
AS	11	Isotopes	Atoms (same element) which have the same proton number, but a different nucleon number / number of neutrons.
	11	Meson	A type of hadron particle that is made up of two quarks.
AS	11	Nucleon (mass) Number	The number of protons together with the number of neutrons in the nucleus is called the nucleon number (or mass number) A
AS	11	Proton Number	The number of protons in the nucleus of an atom ( aka atomic number) Z
AS	11	The Atom	The simple model of the atom is made up of three sub-atomic particles: The proton (which is positively charged), the neutron (which is uncharged but equal in mass to the proton), & the electron (which is negatively charged & equal to the charge on the proton, but much smaller in size & mass).

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A2 Level Physics Terms & Concepts

Useful set of flashcards for A2 revision

• https://quizlet.com/392317817/cie-physics-a-level-definitions-flash-cards/ 

 

Lvl	Ch	Term	Definition
A2	12	Angular displacement	the angle through which the object has moved
A2	12	Radian	angle subtended at the centre of a circle by an arc of length equal to the radius of the circle
A2	12	Angular velocity	rate of change of angular displacement
A2	12	Angular acceleration	rate of change of angular velocity
A2	13	Newton’s Law of Gravitation	any two point masses attract each other a force that is directly proportional to the product of their masses and inversely proportional to the square of the separation
A2	13	Gravitational field strength, g	gravitational force exerted per unit mass on a small object placed at that point
A2	13	Field of force	A region of space where a force acts (on a particle of certain property)
A2	13	Gravitational potential	work done per unit mass in bringing unit mass from infinity to the point
A2	13	Geostationary orbits	Orbit in which a satellite is positioned so that it orbits the Earth the same rate as the Earth’s rotation. Satellite remains above a fixed point on the Earth’s surface
A2	15	Mole	amount of that substance which contains the same number of particles as there are in 0.012 kg of carbon-12
A2	15	Avogadro's constant	amoung of carbon-12 atoms in 12g of Carbon-12
A2	15	Boyle’s law	pressure exerted by a fixed mass of gas is inversely proportional to its volume, provided the temperature of gas remains constant
A2	15	Charles’ Law	temperature acting on a fixed mass of gas is directly proportional to its volume, provided the pressure of gas remains constant
A2	15	Ideal gas	Gas that behaves and obeys all law
A2	14	Thermal Equilibrium	a condition when two or more objects in contact have the same temperature so that there is no net flow of thermal energy
A2	14	Thermocouple	device consisting of wires of two different metals across which an emf is produced when the two junctions of the wires are at different temperature
A2	14	Temperature	Amount of average kinetic energy of particles, and shows direction of net heat flow between two bodies in contact.
A2	14	Fixed points	Standard reference temperatures that are used when calibrating thermometers.
A2	14	Absolute zero	Temperature at which atoms have minimum or zero energy.
A2	14	Calibration	Uses fixed points as upper/lower points and assumes a linear change of property with temperature.
A2	14	Thermodynamic / Absolute Scale	Scale does not depend on the property of a substance
A2	16	Internal energy	sum of the random distribution of kinetic and potential energies of its atoms or molecules
A2	16	First Law of Thermodynamics	the increase in internal energy of a body is equal to the thermal energy transferred to it by heating plus the mechanical work done on it
A2	14	Heat / Thermal Energy	energy transferred from one object to another because of temperature difference. Increases internal energy.
A2	14	Specific heat capacity	energy required per unit mass of the substance per unit °C to raise the temperature by 1 K or 1°C.
A2	14	Specific latent heat	energy required per kilogram of the substance to change its state without any change in temperature
A2	14	Specific latent heat of fusion	energy required per kilogram of a substance to change it from solid to liquid without a change in temperature
A2	14	Specific latent heat of vaporisation	energy required per kilogram of a substance to change it from liquid to gas without a change in temperature
A2	14	Boiling	The process by which a liquid changes into its gaseous state at a constant specific temperature, known as boiling point. Heat energy goes towards overcoming intermolecular forces to move the atoms far enough so that interatomic forces and potential energy are negligible.
A2	16	Brownian Motion	The haphazard or random movement of tiny suspended particles (such as smoke, pollen etc.) in a fluid is known as Brownian Motion.
A2	14	Evaporation	The process by which molecules on the surface of a liquid with sufficient Kinetic Energy break from the attractive intermolecular forces of the liquid & escape as gas particles. This process occurs below the boiling point of a liquid.
A2	16	Kinetic Theory Of Gases:	The molecules are in rapid, random motion. Collisions between gas molecules/container wall are elastic. Intermolecular forces of repulsion only act during collisions between the molecules. The duration of collisions as compared to the time interval between collisions is negligible. The volume that the molecules themselves take up is negligible in comparison to the volume of the container itself.
A2	14	Melting	The process by which a solid changes into its liquid state at a constant specific temperature, known as melting point. Heat energy is used to overcome rigid forces between atoms. Potential energy increases, but kinetic energy is constants.
A2	17	Amplitude	maximum displacement from the equilibrium position
A2	17	Period	time taken to complete one complete cycle
A2	17	Simple Harmonic motion	Acceleration is directly proportional to its displacement from its equilibrium position, and always directed towards equilibrium position. Acceleration and displacement are both in opposite directions.
A2	17	Damping	oscillations/amplitude/energy decreases through time due to friction/external forces/loose to surrounding
A2	17	Fundamental frequency	the lowest frequency stationary wave for a particular system
A2	17	Natural frequency	the unforced frequency of oscillation of a freely oscillating object
A2	17	Forced oscillation	oscillation caused by an external driving force whose frequency equal to that of the driving force
A2	17	Free oscillation	oscillation whose frequency is the natural frequency of the oscillator.
A2	17	Resonance	System forced to vibrate close to its natural frequency, the amplitude of vibration increases rapidly. Frequency of external force equals to the natural frequency, and amplitude is maximum.
A2	24	Acoustic impedance	product of the density of a substance and the speed of sound in that substance
A2	24	Impedance matching	reduction in intensity of reflected ultrasound at the boundary between two substances
A2	24	Transducer	device that changes one form of energy into another
A2	24	Attenuation	Exponential decrease of wave intensity/power/amplitude as it travels a distance in a medium due to energy absorption by medium
A2	24	Reflection coefficient	Fraction/percentage of wave intensity reflected at a boundary between mediums of different impedance
A2		Modulation	process of using one waveform to alter the frequency, amplitude or phase of another waveform
A2		Carrier wave	a waveform that is modulated with an input signal to carry information
A2		Amplitude modulation (AM)	Amplitude of a carrier wave is made to vary in synchrony with the displacement of the information signal.
A2		Frequency modulation (FM)	Frequency of a carrier wave is made to vary in synchrony with the displacement of the information signal.
A2		Bandwidth	measure of the width of a range of frequencies being transmitted
A2		Sidebands	band of frequencies above or below the carrier frequency produced as a result of modulation
A2		Analogue signal	signal that is continuously variable, having a continuum of possible values
A2		Digital signal	signal that has only a few possible values, often two
A2		ADC	conversion of a continuous analogue signal to discrete digital numbers
A2		DAC	conversion of a series of digital numbers into a continuous analogue signal
A2		Bit	basic unit of information storage stored by a device that exists in only two distinct states
A2		Noise	Unwanted power on signal that is random
A2		Regeneration	restoring a signal to its original form/ removing noise/ increasing signal strength
A2		Attenuation	Loss in power or intensity of a signal
A2		Base station	receiver and transmitter used to maintain contact with a number if mobile phones in a local area
A2		Cellular exchange	a switching centre connecting all the base stations in an area
A2		Coaxial cable	electrical cable with an inner conductor surrounded by a tubular insulating layer and an outside conducting layer
A2		Decibel	logarithmic unit of measurement that expresses the relative sizes of two powers
AS		Electric Field	Area / region of space where a charge experiences an electric force.
		Electric Field lines	Line spacing represents electric field strength. The lines of force start on a positive charge, and end on a negative charge, and never touch or cross.
A2	18	Coulomb’s law	any two point charges exert an electrical force on each other that is proportional to the product of their charges and inversely proportional to the square of the distance between them
A2	18	Coulomb	a charge of 1 C passes a point when a current of 1 A flows for 1 s.
A2	18	Electric potential	work done per unit positive test charge in bringing it from infinity to that point
A2	18	Field of force	A region of space where a force acts on a charged particle
A2	18	Electric field strength	Electric force per unit positive test charge
A2	19	Capacitance	Ratio of charge stored in one plate of a capacitor to the potential difference across capacitor
AS	9	Sensing Device	Detects or monitor physical properties and converts it into an electrical property
A2		Processing Unit	Operates on signal from sensing devices and gives an output votlage signal
A2		Comparator	A circuit to compare the inverting and non-inverting input of op-amp
A2		Negative Feedback	Process where a fraction of output is combined to the input. This output fraction is subtracted from the input (because output is 180° out-of-phase with input)
A2		Inverting Amplifier	A circuit to produce an output signal that is proportional to the input signal where the output signal has the OPPOSITE sign/polarity as input signal.
A2		Non-inverting Amplifier	A circuit to produce an output signal that is proportional to the input signal where the output signal has the SAME sign/polarity as input signal.
A2		Virtual earth	A point in the circuit where potential is zero. If non-inverting input (V+) is grounded, so inverting input (V-) must also be 0V so that the op-amp does not saturate. Gain of op-amp is infinite, so any difference between the inputs saturates the output.
A2	20	Magnetic field	A region of space where a magnetic pole, current-carrying conductor, or moving charge experiences a magnetic force
A2	20	Magnetic flux density	Force per unit length of a straight conductor carrying 1A current normal to a uniform magnetic field. Or force per unit charge travelling at right-angles to a uniform magnetic field.
A2	20	Tesla	when a wire carrying a current of 1 A placed at right angles to the magnetic field experiences a force of 1 N per metre of its length
A2		Precession	Rotation of nuclei about the direction of magnetic field due to its spin.
A2		Larmor frequency	Angular frequency along the nuclear spin axis that rotates in a horizontal circle.
A2		Nuclear resonance	Pulse of radio frequency at Larmor frequency that causes protons to absorb energy and flip into a high energy state temporarily.
A2		Relaxation time	time taken for the nuclei to fall back to their lower energy state
A2	20	Faraday’s law	the induced emf is proportional to the rate of change of magnetic flux linkage
A2	20	Lenz’s Law	Direction of induced current creates a magnetic field that opposes the change causing it
A2	20	Magnetic flux linkage	product of magnetic flux and the number of turns
A2	20	Magnetic flux	product of magnetic flux density normal to a circuit and the cross-sectional area of the circuit
A2	20	Eddy currents	Induced currents in large conductors (e.g. iron cores) that dissipate electrical energy as thermal energy (heat). Reduced by laminating the conductor.
A2	21	rms current	Value of direct current that produces same mean power or heating as the alternating current in a resistor
A2	21	smoothing	reduction in the range/variation of output voltage or current so that output does not fall to zero
A2	21	Ideal transformer	Changes the magnitude of potential difference (by mutual inductance of two coils) with no power loss in transformer
A2	21	Soft iron core	Easily magnetized and demagnetized material to concentrate the magnetic flux and imncrease flux linkage. Can be laminated to reduce energy loss due to eddy currents
A2	22	Photons	little packets of energy of electromagnetic wave/energy
A2	22	Absorption line spectrum	a dark line of a unique wavelength seen in a continuous spectrum
A2	22	Emission line spectrum	a sharp and bright line of a unique wavelength seen in a spectrum
A2	22	Electronvolt	the energy gained by an electron travelling through a p.d. of 1 V.
A2	22	Elementary charge	the smallest unit of charge that a particle can have
A2	22	Photoelectric effect	Emission of electrons from a surface when electromagnetic radiation is incident on the surface.
A2	22	Threshold frequency	minimum frequency required to release electrons from the surface of a metal
A2	22	Work function	minimum amount of energy required by an electron to escape its surface
A2	22	DeBroglie wavelength	wavelength of a particle that is moving
A2		Energy band	Atoms close together causes discrete energy levels in each isolated atom to spread out and form an energy band in a solid.
A2		Conductor	Substance where the valence band overlaps with conduction band, and electrons inside conduction bad are available charge carriers. Lattice vibration due to higher temperatures hinders the movement of charge carriers and causes resistance to increase.
A2		Semiconductor	Substance where the empty conduction band and valence band (fully occupied by electrons) are separate by a narrow forbidden band. A higher temperature or light intensity gives energy to electrons to jump into the conduction band. Increase of charge carriers (electons in CB and holes in VB) causes decrease in resistance.
A2	24	Braking radiation	X-rays produced when electrons are decelerated
A2	24	Characteristic radiation	very intense X-rays produced in an X-ray tube having specific wavelengths that depend on the target metal
A2	24	Collimated beam	parallel-sided beam of radiation where area of beam is constant
A2	24	Contrast media	Used to review the outlines or edges of soft tissues in an X-ray image. Materials that easily absorb X-rays
A2	24	Attenuation	Exponential decrease of wave intensity/power/amplitude as it travels a distance in a medium due to energy absorption by medium
A2	24	Voxel	small cube in a 3D picture, the equivalent of a pixel in a 2D picture
A2	23	Isotopes	Same atomic number but different nucleon number. Same number of proton but different number of neutron
A2	23	Nuclide	One type of nucleus with a particular nucleon number and a particular proton number
A2	23	Nucleus	tiny central region of the atom that contains most of the mass of the atom and all of its positive charge
A2	23	Rest mass	mass when it is stationary
A2	23	Einstein’s Equation	mass of system increases when energy is supplied to it
A2	23	Mass defect	difference between total mass of the individual, separate nucleons and the mass of the nucleus
A2	23	Binding energy	minimum energy needed to pull a nucleus apart into its separate nucleons
A2	23	Radioactive decay	Random and spontaneous emission of particles (alpha/beta) and electromagnetic radiation (gamma) by an unstable nucleus
A2	23	Random	difficult to predict which nuclei would decay
A2	23	Spontaneous	nuclei will decay without any external factors
A2	23	Half-life	mean time taken for half the number of active nuclei in a radioactive sample to decay
A2	23	Decay constant	probability of an isotope decaying per unit time interval
A2	23	Nuclear fission	the splitting of a nucleus into two large fragments and a small number of neutrons
A2	23	Nuclear fusion	a nuclear reaction where two light nuclei join together to form a heavier but more stable nucleus

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