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Physics A2 > All definitions > Flashcards

All definitions Flashcards

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1
Q

Angular displacement

A

The angle through which an onbject moves in a circle

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2
Q

Radian

A

One radian is the angle subtended at the centre of a circle by an arc of length equal to the radius of the circle

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3
Q

Angular velocity

A

The rate of the change of the angular position of an object as it moves along a curved path

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4
Q

Newtons first law

A

An object will remain at rest or keep travelling at constant velocity unless it is acted on by a resultant force

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5
Q

Centripetal force

A

The resultant force acting on an object moving in a circle it is always derected towards the centre of the circle

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6
Q

Newtons secound law

A

The resultant force acting on an object is equal to the rate of change of its mommentum. The resultant force and the change in momentum are in the same direction.

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7
Q

Absolute scale

A

A scale of temperature

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8
Q

Absoulte zero

A

The temperature at which a system has minimum internal energy:equivalent to -273.14 degress c

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9
Q

Absorpution line spectrum

A

A dark line of a unique wavelength seen in a contunuous spectrum

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10
Q

Acoustic impendance

A

Acoustic impendance is the product of the density of a substace and the speed of sound in that substance

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11
Q

Activity

A

The rate of decay o disinitergration of nuclei in a radioactive sample

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12
Q

Amplitude

A

The maximum displacement of a particle from its equilibrium position

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13
Q

amplitude modulation

A

A form of modulation in which the signal causes variations in the amplitude of a carrier wave.

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14
Q

Analogue signal

A

A signal that is continuously variable, having a continuum of possible values.

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15
Q

analogue-to-digital conversion (ADC)

A

Conversion of a continuous analogue signal to discrete digital numbers.

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16
Q

angular frequency

A

The frequency of a sinusoidal oscillation expressed in radians per secound.

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17
Q

Atomic mass unit

A

A unit of mass approcimately equal to 1.6661x10-27 kg. The mass of an atom of carbon 12 is 12atomic uni mass exactly

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18
Q

attenuation

A

The gradual loss in strength or intenstiy of a signal

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19
Q

Avogadro constance

A

The number of particles in one mole of any substance, denoted NA (the A is subscript)

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20
Q

Band theory

A

The idea that electrons in solid or liquid can have energies within certain ranges or bands, between whicha re forbidden values.

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21
Q

Bandwidth (communication)

A

A measure of the width of a range of frequencies being transmitted.

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22
Q

Binding energy

A

The minimum external energy required to seperate all the neutrons and protons of a nucleus.

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23
Q

bit

A

A basic unit of informatino storage, the amount of information stored by a device that exsists in only two distinct states, ususally given as the binary digits 0 and 1

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24
Q

Boltzmann constant

A

A fundamental constant, which is equal to the ideal gas divided by avagadro constant

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25
Q

Boyle’s law

A

The pressure exerted by a fixed mass of gas is inversely proportional to its volume, provided the temperature of the gas remiains the same.

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26
Q

braking radiation

A

X-Rays produced when electrons are decelerated (also clled bremsstrahlung radiation)

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27
Q

carrier wave

A

A waveform (usually sinusoidal) which is modulated by an input signal to carry information

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28
Q

characeteristic radiation

A

very intense X-rays produced in an X-ray tube, having specific wavelengths that depends on the target metal.

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29
Q

Charge carrier

A

Any charge particle sucha as an electron responsible for a current

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30
Q

Charles’s law

A

The vloume occupied by a gas at constant pressure is directly proportional to its thermodynamic (absolute) temperature

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31
Q

closed system

A

A system of interacting objects in which there are no external forces.

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32
Q

coaxial cable

A

an electrical cable with an inner conductor surrounding by a tubular inisulating layer and an outside conducting layer.

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33
Q

coherent

A

Two sources are coherent when they emit waves with a constant phase difference.

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34
Q

collimated beam

A

A paralled-sided beam of radiation.

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35
Q

compression

A

A region in a sound wave where the air pressure is greater than its mean value.

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36
Q

Compressive

A

Describes a force that squeezes an object

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37
Q

computerised axial tomography

A

A technique in whihc X-rays are used to image the human body in order to produce a computerised 3-D image.

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38
Q

conduction band

A

A range of electrons energies in a solid; electrons in the conduction band are free to move throughout the material.

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39
Q

Conservation of momentum

A

In a closed system, when bodies interact, the total momentum in any specified direction remains constant.

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40
Q

constructive interference

A

when two waves reinforce to give increased amplitude

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41
Q

contact force

A

the force a object exerts on another with which it is in contact

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42
Q

contrast

A

In a high-constrast image, there is a big difference in brightness between bright and dark areas.

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43
Q

Contrast media

A

Materials such as barium that easily absorb X-Rays. A contrast medium is used to reveal te outlnes or edges of soft tissues in an X-Ray image.

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44
Q

coulomb

A

The SI unit of electrical charge (abbreviated to C)

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45
Q

coulomb’s law

A

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.

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46
Q

count rate

A

the number of particles (alpha or beta) or gamma-ray photons decteded per unit time by a Geiger-Muller tube. Count rate is always a fractino of the activity of a sample

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47
Q

couple

A

A pair of equal and antiparallel forces having a turning effect but no resultant force

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48
Q

Damped

A

Describes an oscillatory motion in which the amplitude decreases with time due to energy losses

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49
Q

de Brogli wavelength

A

The wavelength associated with a moving particle

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50
Q

Decay constant

A

It is the probability of an individual nucleus decaying per unit time interval

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51
Q

descibel

A

A logarithmic unit of measurements that expresses the realtive size of two powers.

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52
Q

density

A

The mass per unit volume of a material

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53
Q

destructive interference

A

When two waves cancel to give reduced amplitude

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54
Q

diffraction

A

the spreading of a wave when it passes through a gap or past the edge of an object

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55
Q

digital signal

A

a signal that has only a few possible values, often onyl two

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56
Q

digital-to-analogue conversino (DAC)

A

conversion of a series of digital numbers into a contiuous analogue signal.

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57
Q

dispersion

A

the splitting of light into its different wavelengths

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58
Q

doppler effect

A

The change in frequency or wavelength of a wave observed when the source of the wave is moving towards or away from the observer (or the observer is moving realtive to the sourcce))

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59
Q

e.m.f

A

The total work done when unit charge is moved round a complete circuit

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60
Q

Einstein relation

A

This refers to the eqatuion for the energy of a photon E=hf

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61
Q

Elastic limit

A

The values of stress beyound which an object will not return to its original dimensions

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62
Q

Elastic potential energy

A

Energy stored in a stretch or compressed material

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63
Q

Electrical charge

A

A property of a body that gives rise to a force on the body when it is within an electric field

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64
Q

electric field

A

A region in which a charged body experiences a force

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65
Q

Electric field strength

A

the force per unit positive charge at a point

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66
Q

electrical potential

A

The erngy per unit charge due to a charged body’s position in an electic field

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67
Q

electrical resistance

A

The ratio of potential difference to current

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68
Q

Electrolyte

A

An electrically conducting solution. The conductino is due to positive and negative ions in the solution

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69
Q

Electromagnetic spectrum

A

The family of waves that travel through a vacuum at speed of 3x10^8

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70
Q

electronvolt

A

The erngy gained by an electron travelling trhough a p.d. of 1 volt

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71
Q

Elementary charge

A

The smallest unit of charge that a particle or an object can have.

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72
Q

emission line spectrum

A

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

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73
Q

energy band

A

A range of permutted electron energies in a solid

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74
Q

energy level

A

A quantised energy state of an electron in an atom

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75
Q

evaporation

A

the process by which a liquid becomes a gas at a temperature below its boiling point

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76
Q

exponetial decay

A

describes the decrease of a quantity where the rate of decrease is proportional to the value of the quanity

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77
Q

farad

A

the unit of capacitance

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78
Q

Faraday’s law of electromagnetic induction

A

THe induced e.m.f is propotional to the rate of change of magnetic flux linkage

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79
Q

field line

A

lines drawn to represent the strength and direction of a field of a force

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80
Q

first law of thermodynamic

A

The increase in internal energy of a body is equal to the thermal energy transferred to it by heating plus the mechaniacl work done on it.

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81
Q

Fleming’s left-hand (motor) rule

A

This rule is used to predict the force experienced by a current-carrying conductor placed in an external magnetic field: Thumb–> motion
First finger –> magnetic field
Secound finger –> conventional current

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82
Q

Flemming right hand (generator) rule

A

This rule is used to predict the direction of the induced current or e.m.f. in a conductor moved at right angles to a magnetic field:
Thumb–> motion
First finger –> magnetic field
Secound finger –> conventional current

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83
Q

forbidden gap

A

A range of energy values which an electron in a solid cannot have

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84
Q

Force constant

A

THe ratio of force to extension for a spring or a wire

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85
Q

forced oscilation

A

An oscillation caused by an external driving force; the frequency is determined by the driving force, and is no the natural frequency of the oscillator

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86
Q

Free oscillation

A

An oscillation that is at its natural frequency of the oscilation

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87
Q

Frequency

A

the number of oscillations per unit time

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88
Q

frequency modulation

A

A form of modulation in which the signal causes variations in the frequency of a carrier wave.

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89
Q

Fundamental frequency

A

The lowest-frequency stationary wave for a particular system

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90
Q

gain

A

the voltage gain of an amplifier is the ratio of the output voltage to the input voltage

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91
Q

geostationary orbit

A

The orbit of an artifiial satellite which has a period equal to one day so that the satellite remains above the same point on the Earth’s equator. From earth the satellite appears to be stationary.

92
Q

Gravitational field

A

A region where any object with mass experiences a force.

93
Q

gravitational field strength

A

The gravitational force experienced by an object per unit mass

94
Q

gravitational potential

A

The gravitational potential energy per unit mass at a point in a gravitational field

95
Q

gravitational potential energy

A

The energy a body has due to its position in a gravitational field.

96
Q

ground state

A

the lowerst energy state that can be occupied by an electron in an atom

97
Q

half-life

A

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

98
Q

half-thickness

A

The mean thickness of an absorbing material required to reduce the intensity of radiation by half

99
Q

hall effect

A

THe production of a voltage across a conductor when a current flows through the conductor at right angles to a magnetic field

100
Q

Hall voltage

A

The voltage produced across a conductor when a current flows through the conductor at right angles to a magnetic fiels; used ni a hall probe to measuer B

101
Q

harmonic

A

a wave of frequency n times the fundamental frequency, where n is an interger

102
Q

Hooke’s Law

A

The extension produced in an object is proportional to the force producing it.

103
Q

idea gas

A

a gas that behaves according to the ideal gas equation Pv=nRT

104
Q

image intensifier

A

A device used to change a low-intensity X-ray image into a bright visual image.

105
Q

impedance matching

A

The reduction in intensity of ultrasound reflected at the boundary between two substances, achived when two substances have similar acoustic impedances

106
Q

inelastic

A

A collision is inelastic when kinetic energy is not conserved; some is transferred to other forms such as heat. Momentum and total energy are always conserved.

107
Q

inertia

A

A measure of the mass of an object. A massive object has a large inertia

108
Q

instantaneous speed

A

The speed of an object measured over a very short period of time

109
Q

intensity

A

The power transimitted normally through a surface per unit area

110
Q

interference

A

The formation of points of cancellation and reinforcement where two coheret waves pass though each other.

111
Q

internal energy

A

The sum of the random distibution of kinetic and potential enegies of the atoms or molecules in a system

112
Q

internal resistance

A

The resistance of an e.m.f. source. The internal resistance of a battery is due to the cheicmals within it.

113
Q

intrinsic semiconductor

A

A pure substance whose resistivity is inetermediate between that of a conductor and an insulator.

114
Q

inverting amplifier

A

A circuit, involving the use of an amplifier, where the output is 180 degress out of phase with the input.

115
Q

kinetic theory of gases

A

A model based on the microscopic motion of atoms or molecules of a gas

116
Q

Kirchoff’s first law

A

The sum of the currents entering any point (or junction) in a circuit is equal to the sum of the currents leaving that same pont. This law represents the conservation of charge

117
Q

Kirchhoff’s secound law

A

The sum of the e.m.f.s round a closed loop in a circuit is equal to the sum of p.d.s in that same loop

118
Q

Larmor frequency

A

The frequncy of precession of nucleus in an external magnetic field

119
Q

Lenz’s law

A

An induced current or e.m.f is in a direction so as to produce effects which oppose the change producing it.

120
Q

light-depending resistor (LDR)

A

A resistor whose resistance decreases as the intensity of light falling on it increases.

121
Q

light-emitting diode (LED)

A

A semiconductor component that emits light when it conducts electricity.

122
Q

linear momentum

A

THe product of an object’s mass and its velocity

123
Q

longitudinal wave

A

A wave in which the particles of the meium oscillate along the direction in which the wave travels.

124
Q

lost volts

A

the difference between the e.m.f. and the terminal p.d. in a circuit. It is equal to the voltage across the internal resistance.

125
Q

magnetic field

A

A force field in which a magnet, a wire carrying a current, r a moving charge experiences a force

126
Q

magnetic flux

A

The product of magnetic flux density normal to a circuit and the cross-sectionaal area of the circuit.

127
Q

magnetic flux density

A

The strength of a magnetic field. defined by the equation F/IL where;
F= force exsperiance by a conducto in the magnetic field
I= the current in the conductor
L= the length of the conductor in the magnetic field (the conductor is at a right angle to the field)

128
Q

magnetic flux linkage

A

the product of magntic flux and the number of turns

129
Q

magnetic resonance imaging

A

A medical imaging techinque which uses nuclear magnetic resonace.

130
Q

mass

A

A measure of the amount of matter within an object

131
Q

mass defect

A

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

132
Q

mass excess

A

the difference between the mass of a nucleide and its mass number

133
Q

microwave link

A

a communications system that uses a beam of radio wave in the microwave frequency range to transmit audio, data or video informtion.

134
Q

modulation

A

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

135
Q

mole

A

THe amount of matter which contains 6.02 x10^23 particles.

136
Q

monochromatic

A

describes light of a single frequency

137
Q

natural frequency

A

The unforced frequency of oscillation of a freely oscillating object

138
Q

negative feedback

A

The output of a system is used to oppose changes to the input of the system, with the result that the changes are reduced.

139
Q

newtons first law of motion

A

An object will remain at rest or keep ttravelling at constant velocity unless it is acted on by a resultatn force.

140
Q

newtons’s law of gravitation

A

any two point masses attract each other with a force that is directly proportional to the product of their masses and invercely propotional to the square of the sepreation

141
Q

newtons’s secoud law of motion

A

the resultant force acting on an object is equal to the rate of change of its momentum. the resutant force and the change in the momentum are in the same direction.

142
Q

newtons third law of motion

A

when two bodies inreact, the forces they exert on eachother are equal and opposite.

143
Q

node

A

A point on a statinoary wave with zero amplitude

144
Q

noise

A

An unwanted random addition to a transmitted signal

145
Q

non-inverting amplifier

A

a citcuit, involving the use of an amplifier, in which the output is in phase with the input.

146
Q

nuclear fission

A

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

147
Q

nuclear fusion

A

A nuclear reaction in which two light nuclei join together to form a heavier but more stable nucleus.

148
Q

nuclear magneti resonance

A

A process in which radio wave absorbed or emitted by nuclei spinning in a magnetic field

149
Q

nuclear model of the atom

A

a model of the atom in which negative charges are distributed outside a tiny nucleus of positive charge

150
Q

nucleon number

A

the number of neutrons and protons in the nucelus of an atom

151
Q

nucleon

A

A particle found in an atomic nucleus

152
Q

nucleus

A

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

153
Q

nuclide

A

a specific combination of protons and neutrons in a nucleus

154
Q

number density

A

the number of particles such as free electrons per unit volume in a material

155
Q

Ohm’s law

A

The current in a metallic conducto is directly proportional to the potnetial difference across its ends, provided its temperature remains constant

156
Q

operational amplifier (op-amp)

A

A high-gain electronic d.c. voltage amplifier with differential inputs and, usually, a single output

157
Q

optic fibre

A

A glass or plastic fibre that caries light along its length

158
Q

oscillation

A

A repetitive back-and-forth or up-and-down motion

159
Q

path difference

A

the difference in the distances travelled by two waves from coherent sources at a partiular point

160
Q

perfectly elastic

A

A collision is perfectly elastic when kinetic energy is conserved, momnetum and total energy are always conserved.

161
Q

period

A

The time taken by an object (e.g.plant) to complete one cycle (e.g. an orbit). The period is also the time taken for one complete oscillation of a vibrating object

162
Q

phase

A

refers to the point that an oscillating mass has reached in a complete cycle

163
Q

phase difference

A

THe difference in the phase of two oscillatin paricles, expressed in degress or radians

164
Q

phottoelectric effect

A

An interaction between a photon and an electron in an atom, in which the electron is removed from the atom.

165
Q

piezo-electric crystal

A

A material that produces an e.m.f. when it is stressed, causing its shape to change. Also, when a voltage is applied across it in one direction, it changes its dimensions slightly

166
Q

piezo-electric effect

A

The production of ane.m.f between the faces of a crystal when the crystal is compressed

167
Q

planck constant

A

The constant which links the energy of a photon and ts frequency, in the equation

168
Q

plum-pudding model

A

A model of the atom in which neagtive charges are distributed throughout a sphere of positvei charge

169
Q

positron

A

an anti-electron

170
Q

potential difference (p.d.)

A

The enrgy lost per unit charge by charges passing through a component

171
Q

potential divider

A

A circuit in which two or more components are connected in series t a supply. The output voltage from the circuit is taken across one of the components.

172
Q

potentiometer

A

A circuit which allows the measurement of an e.m.f. by comparison with a known e.m.f.

173
Q

precession

A

the movement of the axis of a spinning object (proton) arouond another axis

174
Q

principle of conervatino of energy

A

The idea that, within a closed system, the total aount of energy in all its forms is unchaged during any change.

175
Q

princple of moments

A

for an object in equilibrium, the sum of clockwise moments about a point is equal to the sum of the anticlockwise moments about the same point.

176
Q

principle of superposition

A

When two or more waves meet at a point, the resultant displacement is the sum of the displacements of the individual wave.

177
Q

progressive wave

A

a wave that carries energy from one place to another

178
Q

range

A

The horizontal distance covered by an object.

179
Q

rarefaction

A

A region in a sound wave where the air pressure is less that its mean value.

180
Q

rectification

A

The process of converting alternating current into direct current

181
Q

red shift

A

The change in frequency or wavelength of a spectral line observed when the souce of light is moving away from the observer

182
Q

regeneration

A

Restoration of a signal to its original form, usually by temoving or reducing nosie and increasing signal strength

183
Q

relaxation time

A

the time taken for a nucleus or other exited system to fall back to a lower energy state.

184
Q

relay

A

an electricaly operated switch caused to open and close by current in a coil

185
Q

repeated

A

An electronic device that receives a signal and retransmits it.

186
Q

resistivity

A

A propoerty of a material, a measure of its electrical resistance

187
Q

resonance

A

The forced motion of an oscillator characterised by maximum amplitude when the forcing frequency matches the oscillator’s natural frequency. A system absorbs maximum energy from a source when the source frequency is equal to the natural frequency of the system

188
Q

right-hand grip rule

A

A rule for finding the direction of the magnetic field a solenoid. If the right hand grips the solenoid with the fingers follwoing the direction of the conventional current around the solenoid, then the thumb points in the direction of the magnetic field.

189
Q

sampling

A

Taking the value of a continuous signal at regular intervals

190
Q

semiconductor diode

A

An electrical component made from a semiconductor material that only conduct in one direction. A diode in ‘recerse bias’ has an infinte resistance.

191
Q

sensor

A

A device that produces an output (usually a voltage) in response to an input.

192
Q

series

A

A term used when components are connected end-to-end in a circuit

193
Q

sharpness

A

The degree of resolution in an image, which determines the smallest item that can be identified

194
Q

simple harmonic motion

A

motion of an oscillator in which its acceleration is directly propotional to its displacement from its equilibrium position and is directed towards that position

195
Q

solenoid

A

A long current-carrying coil used to generate a uniform magnetic field within its core.

196
Q

specific heat capacity

A

The energy required per unit mass of a substance to raise its temperature by 1k

197
Q

specific latent heat of fusion

A

The energy required per unit mass of a substance to change it from solid to liquid without a change in temperature

198
Q

specific latent heat of vaporisation

A

The energy required per unit mass of a substance to change it from liquid to gas without a change in temperature

199
Q

spin

A

A fundamental property of a subatomic particles which is conserved during atomic and nuclear reactions.

200
Q

stationary wave

A

A wave pattern produced when two progressive waves of the same frequency travelling in opposite directions combine. it is characterised by noes and antinodes. Also know as a standing wave.

201
Q

Strain energy

A

The the potential energy stored in an object when it is deformed eleastically.

202
Q

strain gauge

A

A device that contains a fine wire sealed in plastic. Its electrical resistance changes when the object to which it is attatched changes shape.

203
Q

terminal p.d.

A

The potential difference across an external resistor connected to an e.m.f. source

204
Q

terminal velocity

A

the maximum velocity of an object travelling though a fluid. The resultant force on the object is zero

205
Q

tesla

A

The SI unit of magetic flux density

206
Q

thermal energy

A

Energy transferred from one object to another because of a temperature difference; another term for heat energy.

207
Q

thermal equilibrium

A

A condition when two or more object in contact have the same temperature so that there is no net flow of energy between them.

208
Q

thermistor

A

A device whose electrical resistance changes when its temperature changes.

209
Q

thermocouple

A

A device consisting of wire of two different metals acorss which an e.m.f. is produced when the two junctions of the wires are at different temperatres.

210
Q

thermodynamic scale

A

A temperature scale in which temperarture is measured in kelvin

211
Q

threshold frequency

A

The minimum frequency of electromagnetic radiation that will eject electrons from the surface of a metal

212
Q

threshold voltage

A

The minimum forward bias voltage across a light-emitting diode (LED) when it starts to conduct and emit light.

213
Q

time constant

A

The time taken for the current, stored charge or p.d. to fall to 1/e (about 37%) of its original value when a capcitor discharges through a resistor. It is also equal to the product of capacitance and resistance.

214
Q

tracers

A

radioactive substances used to investigate the functions of organs of the body.

215
Q

transducer

A

A general term used for any device that changes from one form of energy into another.

216
Q

transition

A

When an electron makes a ‘jump’ between two energy levels.

217
Q

transverse wave

A

A wave in which the particles of the mediiumm oscillate at right angles to the direction in which the wave travels.

218
Q

turns-ratio equation

A

An equation relating the ratio of voltage to the ratio of numbers of turns on the two coils of a transformers.

219
Q

upthrust

A

The upwards force that a liquid eerts on a body floating or immersed in a liquid

220
Q

valence band

A

A range of electron energies in a solid; electrons in the valence band are bound to individual atoms.

221
Q

Virtual earth approximation

A

An approximation in which the two inputs of an op-amp are nearly at the same potential.

222
Q

viscous forces

A

Forces that act on a body moving through a fluid that are caused by the resistance of the fluid.

223
Q

voxel

A

A small cube in a three-dimension image, the equivalent of pixel in a two-dimensional image.

224
Q

wire-pair

A

A type of electrical wiring in which the two conductos needed to carry a signal are placed close together.

225
Q

work function

A

the minimum energy required by a single electron to escape a metal surface.

226
Q

X-ray tube

A

A device that produces X-ray when accelerated electron hit a target metal

Physics A2 (1 decks)

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