A Level Physics - A2

All the definitions you need to know for your A2 theory exam

Angular Displacement

the angle through which the object has moved

Radian

The angle subtended at the centre of a circle by an arc of equal length to its radius.

Angular velocity

rate of change of angular displacement

Angular acceleration

the rate of change of angular velocity.

Gravitational field strength, g.

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

Newton’s law of gravitation

The gravitational force between two point masses is proportional to the product of the masses and inversely proportional to the square of their separation

Field of a force

a region of space where a force acts

Gravitational potential

The work done per unit mass in bringing a mass from infinity to that point.

Geostationary orbit

The orbit in which a satellite is positioned so that it orbits the Earth at the same rate as its rotation

Mole

Amount of substance that contains the same amount of particles as there are in Carbon-12

Avogadro’s Constant

Amount of Carbon-12 atoms in 12 atoms of Carbon-12

Boyle’s Law

Pressure exerted by a fixed mass of gas is inversely proportional to its volume, provided the temperature of gas remains constant.

Pressure Law

The pressure of a gas is directly proportional to its absolute temperature, when the volume remains constant.

Charles’ Law

Temperature acting on a fixed mass of gas is directly proportional to its volume, provided the pressure of gas remains constant.

Ideal Gas

Gas that behaves and obeys all laws

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

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

Temperature

Amount of average kinetic energy of particles, and shows direction of net heat flow between two bodies in contact.

Fixed points

Standard reference temperatures that are used when calibrating thermometers

Absolute Zero

Temperature at which atoms have minimum or zero energy

Calibration

Uses fixed points as upper/lower points and assumes a linear change of property with temperature

Thermodynamic / Absolute Scale

Scale does not depend on the property of a substance

Internal Energy

Sum of the random distribution of kinetic and potential energies of its atoms or molecules

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

Thermal Energy

Energy transferred from one object to another because of temperature difference. Increases internal energy

Specific Heat Capacity

Energy required per unit mass of the substance per unit °C to raise the temperature by 1 K or 1°C

Specific Latent Heat

Energy required per kilogram of the substance to change its state without any change in temperature

Specific Latent Heat of Fusion

Energy required per kilogram of a substance to change it from solid to liquid without a change in temperature

Specific Heat of Vapourisation

Energy required per kilogram of a substance to change it from liquid to gas without a change in temperature

Boiling

The process by which a liquid changes into its gaseous state at a constant specific temperature, known as boiling point.

Brownian Motion

The haphazard or random movement of tiny suspended particles (such as smoke, pollen etc.) in a fluid

Evaporation

the process by which molecules on the surface of a liquid with sufficient K.E break from the attractive intermolecular forces of the liquid & escape as gas particles

Kinetic Theory

assumes that ideal gas molecules:
- are constantly moving
- have negligible volume
- have negligible intermolecular forces
- undergo perfectly elastic collisions
- have an average kinetic energy proportional to the ideal gas's absolute temperature.

Melting

The process by which a solid changes into its liquid state at a constant specific temperature (P.E increases, K.E is constant)

Amplitude

maximum displacement from the equilibrium position

Period

time taken to complete one complete cycle

Simple Harmonic Motion

acceleration is directly proportional to its negative displacement from its equilibrium position

Damping

oscillations decrease through time due to the loss of energy to surrounding

Light Damping

amplitude decreases gradually with time

Critical Damping

oscillations die away more quickly

Heavy Damping

the displacement decreases to zero in the shortest time, (0 oscillations)

Fundamental Frequency

the lowest frequency stationary wave for a particular system

Natural Frequency

the unforced frequency of oscillation of a freely oscillating object

Forced Oscillation

oscillation caused by an external driving force whose frequency equal to that of the driving force

Free Oscillation

oscillation whose frequency is the natural frequency of the oscillator

Resonance

driving force = natural force, which causes a decrease in amplitude

Acoustic Impendence

product of the density of a substance and the speed of sound in that substance

Impedance Matching

reduction in intensity of reflected ultrasound at the boundary between two substances

Transducer

a device which converts energy

Attenuation

reduction in wave intensity as it travels through a medium

Reflection Coefficient

fraction/percentage of wave intensity reflected at a boundary between mediums of different impedance

Modulation

process of using one waveform to alter the frequency, amplitude or phase of another waveform

Tracer

a substance that consists of radioactive material attached to the natural material (FDG)

Annihilation

when a particle (e-) hits an antiparticle (e+)

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.

Coulomb's Law

the electrical force between two point charges is proportional to the product of the charges and inversely proportional to the square their separation

Coulomb

a charge of 1 C passes a point when a current of 1 A flows for 1 s (product of current and time)

Electric Potential

the work done per unit mass in bringing a unit positive charge from infinity to that point

Field of Force

a region of space where a force acts on a charged particle

Electric Field Strength

electric force per unit positive test charge

Capacitance

ratio of charge stored in one plate of a capacitor to the potential difference across capacitor

Magnetic Field

region of space where a magnetic pole, current-carrying conductor, or moving charge experiences a magnetic force

Magnetic Flux Density

force per unit length of a straight conductor carrying 1A current normal to a uniform magnetic field

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

Faraday's Law

the induced emf is proportional to the rate of change of magnetic flux linkage

Lenz's Law

direction of induced current creates a magnetic field that opposes the change causing it

Magnetic Flux

product of magnetic flux and the number of turns

Magnetic Flux Linkage

product of magnetic flux density normal (perpendicular) to a circuit and the cross-sectional area of the circuit

Eddy Currents

induced currents in large conductors (e.g. iron cores) that dissipate electrical energy as thermal energy (heat). (reduced by laminating the conductor)

rms current

value of direct current that produces same mean power or heating as the alternating current in a resistor

smoothing

reduction in the variation of output voltage/current so that output does not fall to zero

Soft Iron Core

easily magnetized and demagnetized material to concentrate the magnetic flux and increase flux linkage

Photons

little packets of energy of electromagnetic wave/energy

Absorption Line Spectrum

a dark line of a unique wavelength seen in a continuous spectrum

Emission Line Spectrum

a sharp and bright line of a unique wavelength seen in a spectrum

Electronvolt

the energy gained by an electron travelling through a p.d. of 1 V

Elementary Charge

the smallest unit of charge that a particle can have

Photoelectric Effect

emission of electrons from a surface when electromagnetic radiation is incident on the surface

Threshold Frequency

minimum frequency required to release electrons from the surface of a metal

Work Function

minimum amount of energy required by an electron to escape its surface

De Broglie Wavelength

wavelength of a particle that is moving

Collimated Beam

parallel-sided beam of radiation where area of beam is constant

Contrast Media

used to review the outlines or edges of soft tissues in an X-ray image. Materials that easily absorb X-rays

Attenuation

reduction in wave intensity as it

Voxel

small cube in a 3D picture, the equivalent of a pixel in a 2D picture

Isotope

same number of proton but different number of neutron

Nuclide

one type of nucleus with a particular nucleon number and a particular proton number

Nucleus

tiny central region of the atom that contains most of the mass of the atom and all of its positive charge

Rest Mass

mass when it is stationary

Einstein's Equation

mass of system increases when energy is supplied to it

Mass Defect

difference between total mass of the individual, separate nucleons and the mass of the nucleus

Binding Energy

minimum energy needed to pull a nucleus apart into its separate nucleons

Radioactive Decay

random and spontaneous emission of particles (alpha/beta) and electromagnetic radiation (gamma) by an unstable nucleus

Random

difficult to predict which nuclei would decay

Spontaneous

nuclei will decay without any external factors

Half-Life

mean time taken for half the number of active nuclei in a radioactive sample to decay

Decay Constant

probability of an isotope decaying per unit time interval

Fission

the splitting of a nucleus into two large fragments and a small number of neutrons

Fusion

a nuclear reaction where two light nuclei join together to form a heavier but more stable nucleus