Physics 9702 A2 Level Definitions

Absolute Zero

The theoretical temperature at which the molecules of a substance have the lowest energy and hence the substance has minimum internal energy and no kinetic energy

acoustic impedance

product of density of medium and speed of sound in medium

Activity

The number of atoms of a radioactive substance that decay per unit time.

amplitude modulation

amplitude of carrier wave varies in synchrony with the displacement of the information signal

Analogue signal

data varies continuously with time and can have any value between two limits

Angular Velocity

the rate of change of angular displacement with respect to time swept out by the radius

Attenuation

gradual reduction or loss in signal power or energy

Avogadro constant

number of atoms of carbon-12 in 0.012 kg of carbon-12

Bandwidth

the range of frequencies that can be amplified by the same amount of an operational amplifier

Binding Energy

The amount of energy needed to split a nucleus completely into its individual nucleons.

Binding Energy per Nucleon

Binding energy divided by the mass or nucleon number of the nucleus.

capacitance

ratio of charge on body and its potential

Centripetal Acceleration

Acceleration which is always perpendicular to the velocity and always acts towards the centre of the circular motion.

Centripetal Force

The resultant perpendicular force acting on an object moving in circular motion

Coaxial cables

a pair of wires arranged so that one wire is shrouded by the other

contrast

difference blackening in different regions due to different absorption coefficient

Coulomb's Law

The force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between the charges.

cross-talk

picking up of signal in one cable from a second nearby cable

damping

continuous loss in energy from the oscillating system due to force always acting in opposite direction to the motion

de Broglie wavelength

wavelength of wave that is associated with a particle that is moving

decay constant

probability of decay of a nucleus per unit time

digital signal

consists of a series of pulses of highs and lows between two discrete levels and has no intermediate values

Electric Field Strength

force per unit positive charge acting on a small stationary positive test charge placed at that point

Electric Potential

work done per unit charge in bringing a positive test charge from infinity to the point (without a change in kinetic energy).

Electronvolt

energy gained by an electron when it is accelerated through a p.d. of one volt.

Faraday's Law

Whenever there is a change in magnetic flux linkage of a circuit or coil, an e.m.f. is induced in the circuit and the magnitude is directly proportional to the rate of change of magnetic flux linkage of the circuit or coil.

fibre-optic transmission

signal is in the form of a series of pulses of light which pass along a glass fibre as a result of total internal reflection

field of force

region (of space) where a body experiences a force

First Law of Thermodynamics

The First Law of Thermodynamics states that the internal energy of a system depends only on the thermodynamic state of the system; the increase in the internal energy of a system is equal to the sum of the heat supplied to the system and the work done on the system.

Forced Oscillation

When the system is forced to oscillate at a frequency other than the natural frequency by a periodic external force.

free oscillations

oscillations with no external forces acting

frequency modulation

frequency of carrier wave varies in synchrony with displacement of information signal

geostationary orbit

an equatorial orbit which stays on the same point on the Earth with a period of 24 hours and moves from west to east

gravitational field

region of space in which a mass experiences a force

Gravitational Field Strength

gravitational force per unit mass experienced by a mass placed at that point

Gravitational Potential

work done per unit mass by an external agent in bringing a mass from infinity to that point without a change in kinetic energy.

Gravitational Potential Energy

the work done by an external agent in bringing the mass from infinity to present location without any change in kinetic energy

Half life

Half life of a radioactive element is the time taken for a sample of atoms to decay to half their initial number.

Half-value thickness

thickness needed to reduce the intensity to half the initial value

Hardness of an X-ray

penetration of X-ray

Heat Capacity T

The quantity of heat required to raise the temperature of the body by 1K.

ideal gas

a gas which obeys Boyle's Law Charles' Law and Pressure Law

Intensity of an X-ray

the rate of arrival of electrons at target

Internal Energy

The sum of the microscopic kinetic and potential energies of the molecules that make up the system due to random motion

isotopes

nuclei having same number of protons but different number of neutrons

Kelvin

The Kelvin is defined as 1/273.16 of the temperature difference between absolute zero and the triple point of water.

Latent Heat

It is the thermal energy required by matter for a change in phase.

Lenz's Law

Lenz's Law states that the direction of the induced current is such as to oppose the change in flux which causes it.

Light emitting diode

a diode which emits light when forward biased

magnetic field

region of space in which a force is experienced current-carrying conductor, moving charge or magnetic poles

Magnetic Flux

Magnetic flux through a plane surface is the product of the area and the magnetic flux density that passes through the area perpendicularly.

Magnetic Flux Density

force per unit length on a straight conductor carrying unit current placed perpendicularly to the field.

Magnetic Flux Linkage

the magnetic flux passing through each turn of the coil multiplied by the number of turns of the coil.

Mass Defect

The difference between the sum of the individual masses of protons and neutrons and the mass of a nucleus.

Mobile phone

a long-range portable electronic device used for mobile communication

Modulation

process of varying either the amplitude or frequency of a carrier wave in synchrony with the displacement of information signal in order to carry information

mole

amount of substance containing same number of particles as in 0.012 kg of carbon-12 isotope

Natural Frequency

The frequency of oscillation when a system oscillates freely without any external force applied.

negative feedback

the process of taking some or all of the output and returned to the inverting input and is out of phase by 180 degrees with the input

Newton's Law of Gravitation/Gravitational Force

Newton's law of gravitation states that the force of attraction between two point masses is directly proportional to the product of their masses and inversely proportional to the square of their distance apart.

noise

unwanted random signal power that distorts the transmitted signal

nuclear fission

splitting of heavy nucleus into two lighter nuclei having approximately the equal mass which are more stable

Nuclear Fusion

Process by which nuclei with mass numbers lower than 56 combine to form nuclei of higher mass numbers which are more stable.

oscillations

backward and forward motion between two limits

Photoelectric Effect

The emission of electrons from a metal as a result of light with sufficiently short wavelength falling on it.

photon

discrete amount of quantum energy of electromagnetic radiation

Piezo-electric effect

the process by which ultrasonic transducer produce ultrasonic waves

potential energy

ability to do work as a result of position or shape of an object

radian

angle subtended at centre of circle by an arc is equal in length to the radius of the circle

Radioactivity

The spontaneous emission of ? or ? radiation by a parent nucleus which results in itself being transformed into a completely different daughter nucleus.

Relay

an electromagnetic switch that uses a small current to switch on or off a larger current

resonance

tendency of a system to oscillate at maximum amplitude of vibration when impressed frequency is equal to the natural frequency of vibration

Retention time

the time taken between time when end of pulse and time when emission of r.f. radiation occurs

RMS value of an Alternating current

It is the value of the steady direct current which would dissipate heat at the same rate in a given resistance as the alternating current.

root-mean-square (r.m.s.) value of alternating current

the value of direct current that provides the same mean power in a resistor as the alternating current

root-mean-square (r.m.s.) value of alternating voltage

the steady voltage which produces the same power in a resistor as the alternating voltage

sharpness

the ease with which the edges can be clearly distinguished

Simple Harmonic Motion

The motion of the body whose acceleration is directly proportional to its displacement from a fixed point (equilibrium position) and is always directed towards that fixed point.

Specific acoustic impedance

product of the density of medium and the speed of the wave in the medium

Specific Heat Capacity

It is the quantity of heat required to raise the temperature of 1kg of the body by 1K.

specific latent heat

thermal energy needed to change the state of a unit mass of a substance without change in temperature

specific latent heat of fusion

thermal energy needed to change the state of a unit mass of a substance from solid to liquid without any change in temperature

Specific Latent Heat of Vaporisation

It is the thermal energy required for 1kg of substance to change from the liquid phase to the gaseous phase without a change in temperature.

Summing amplifier

when two or more are fed into input with negative feedback

tesla

the unit of magnetic flux density in which a uniform field normal to a long straight conductor carrying a current of one ampere exerts a force of one Newton per metre on the conductor

Thermal Equilibrium

When two objects in thermal contact cease to have any exchange of heat.

threshold frequency

minimum frequency for electron to be emitted from a cold metal surface of electromagnetic radiation

Triple Point of Water T

The particular temperature and pressure at which the three states of water can co-exist in equilibrium.

Uniform Circular Motion

The motion of an object moving in circular path at constant speed with constant angular velocity.

Uniform Electric Field

Electric field strength is equal in magnitude and has the same direction at all points in the region.

virtual earth

op-amp has a very large gain non-inverting input is earthed so if the amplifier is not to saturate, the inverting input must be almost equal to zero volts

Weber

One Weber is the magnetic flux if a field of flux density one tesla exists at right angles to an area of one metre square.

Wire pairs

a pair of insulated copper wires

Work function

minimum amount of photon energy required to remove a free electron from the surface of a cold metal