Physics Flashcards
(149 cards)
1
Q
insulators and friction
A
when 2 insulators move relative to each other, friction between the two can result in both objects becoming electrically charged
one becomes positively charged, one negatively
conductors can also become charged but will only retain that charge if insulated from the surroundings
2
Q
charging by induciton
A
it is possible for objects to become charged by induction
a neutral object placed near a charged object can become charged
if one end of an object charged by induction is momentarily earthed, allowing the charge that has accimilated at that end to leak away, then the object becomes permenantly charged
3
Q
what is charging
A
when an atom loses an electron it has more protons than electrons so becomes positively charged.
when an atom gains an electron is has more electrons that protons so becomes negatively charged
when two objects rub together, the firction can rsult in electrons being transferred from one to another, resulting in the objects becoming electrostatically charged
charge is always caused by movement of electrons
4
Q
sparking - electrostatic charge
A
sparkin occurs when the air between two objects becomes ionised by a large voltage and therefore starts conductin.
two charged objects that have air between them can discharge a spark between them.
this will happen either when the charge becomes large enough or when the distance between the objects becomes small enough.
the risk of sparking can be eliminated by earthing. if 2 objects that would otherwise cause each other to become charged by friction are connected together by a wire, then electrostatic charging cannot take place
5
Q
photocopying charge
A
scanning process results in charge being placed on the paper at the locations where the image is to be printed
the paper is the exposed to toner powder, which sticks to the paper at those locations as a result of electrostatic induction
paper is then heated so that the toner powder melts and then re-solidifies on the paper
6
Q
aircraft refuelling charge
A
large volumes of fuel flow through the pipe very quickly.
this creates a large amount of friction, resulting in the fuel and the pipe becoming electrostatically charged.
any sparking presents a significant risk of explosion o the fuel in the fuel tank
so they are earthed before refuelling takes place, preventing the build up of charge
7
Q
AC abd DC current
A
DC direct current always in the same direction
AC alternating current repeatedly changes direction
8
Q
DC
A
cells or batteries are sources of DC
the output from a power supply from mains electricity can be converted from AC to DC using diodes as a rectifier
a diode only allows current in one direction
9
Q
AC
A
generators in power stations produce ac
the current regularly changes direction and the change is repeated regularly to produce a waveform that can be seen on an oscilloscope
in the UK and europe the mains supply is 50Hz
the current changes direction 100 times each second ( 50 complete cycles)
10
Q
conductors vs insulators
A
conductors - al metals, carbon (graphite), ionic solutions
offer very little resistance to the flow of electric charge
good insulators - non-metals, plastics, rubber
offer a large resistance to the flow of charge
11
Q
current equation
A
I = Q/t
current = charge / time
Q = electric charge, measured in coulombs
I = rate of flow of electric charge (current)
measured in amps
12
Q
metals as good conductors
A
contain free electrons that can move through the metal and carry their charge
if a voltage is connected across a metal, the positive end of the metal attracts electrons and the negative end repels electrons, creating a flow of charge (current)
current is from the positive end of a conductor to the negative end, electron flow from negative to positive
13
Q
voltmeter
A
connected in parallel with a component and measures voltage
has a very high resistance or else it would short circuit the component as there would be a significant amount of current in the voltmeter instead of the component
14
Q
ammeter
A
connected in series with a component and measures current
very low resistance or it would reduce the amount of current it was being used to measure
15
Q
resistance equation
A
resistance = voltage / current
R = V/ I
resistance measured in ohms
16
Q
ohm’s law
A
for some components, the current is directly proportional to the voltage causin it
V = I x constant
the constant is the resistance of the component
V = I x R
17
Q
fixed resistor
A
a fixed resistor at a constant temperature has a constant resistance
it is an ohmic conductor (obeys Ohm’s law) so R = V / I
the graph of V agains I is directly proportional passing straight through the origin
18
Q
filament lamp
A
emits light because its filament becomes very hot
because its temp changes as its current changes, the resistance is not constant
as the temp increases, the resistance also increases, so a graph of V against I would be a curve
19
Q
thermistor
A
resistor with a resistance that depends on temperature
common type, as temp increases resistance decreases
20
Q
light dependent resistor
A
resistance depends on the intensity of the light.
as light intensity increases, the resistance of the LDR decrea
21
Q
ideal diode
A
a diode is a component that only allows current to flow in one direction
the direction of current allowed is shown by arrowhead on the diode
22
Q
current and voltage rules for series circuit
A
for components in series circuits, the current in each component is the same
for components connected in series, the total voltage across the components is the sum of the voltages across each individual component
23
Q
current and voltage rules in parrallel circuits
A
voltage across each component is the same
at each branch the total current moving into the branch is equal to the total current moving out of it
24
Q
basic concepts of an electric circuit
A
charged particles travel around the loop, picking up energy at the supply, carrying it around one side of the loop to the load, then returning to the supply.
the rate at which charged particles pass around the circuit is the current
the difference in energy carried by each unit of charge at either side of a circuit component is voltage
25
series circuits
there is only one way around the circuit so the charge passing at any point will be the same
the energy transferred at both load one and load 2 is equal to the energy gained at the supply - the voltages across the two loads add up to the supply voltage
26
parrallel circuit
the current in both loads add up to the supply current
the energy transferred to load 1 by each unit is the same as that transferred to load 2 and is the same to that picked up by the supply. the voltages across the two loads are equal
27
resistors in series
the combined resistacne of two or more resistrors connected in series is the um of the individual resistances
28
resistors in parralell
the combined resistance of two or more resistors is always less than the resistance of any of the individual resistors
for two resistors of resistance R connected in series, the combined resistance is R/2
29
voltage equation
voltage = energy / charge
V = E / Q
when a current flows in a circuit, charged particles carry energy from the supply to the components. when the charge passes through a component, some energy is transferred between the charged particles and the component and the particles have different energy before passing the component compared to after.
the voltage across the component is the energy transferred per unit charge.
30
voltage vs current
current is the rate at which the charged particles move around the circuit.
voltage is the energy that each charged particle transfers when passing through a component
31
power equation
power = current x voltage
P = IV = I^2 x R
32
energy transfer equation
energy tranfer = power x time
33
permenant magnets
have a north pole and a south pole
like poles repel, unlike poles attract
the forces are strongest when the magnetic poles are closes and get weaker as the distance increases
the north or south pole of a magnet will attract certain magnetic materials, eg iron, cobalt, nickel
34
north seeking and south seeking
north seeking - attracted to the north geographic pole of the earth
south seeking - attracted toward the geographic south pole of the earth
35
magnetic compass
consists of a bar magnet pivoted about its centre inside a case
can be used for navigation, identifying the poles od a magnet and to trace the pattern of magnetic fields
36
magnetic field pattern around a bar magnet
magnetic field is a region of spance in which magnetic forces act on magnets or magnetic materials
magnetic field lines - start on north poles and end on south poles
cannot start or end in space, cannot cross one another
they point in the direction of force that would be exerted on a free north pole (north to south)
are closer together where the field is stronger
37
soft vs hard magnetic materials
soft - are easy to magnetise but also easily lose their magnestisation
hard - difficult to magnetise but once the are, they are difficult to demagnetise
38
induced magnetism
when either pole of a bar magnet is held close to an unmagnetised magnetic material there is a force of attraction between the magnet and the material
the magnetic field of the bar magnet has induced magnestism on the material.
oppositr magnetic poles attract, and when a north pole induces magnetism it induces a south pole
induced magnestism can be used to make permenant magnets. if an unmagnetised sample of a hard magnetic material is placed in a strong magnetic field then magnetic poles are induced onto the ends of the sample
39
magnetic effect of a current
electric currents create magnetic fields in the surrounding space
if you place a compass close to a current carrying conductor and switch the current on and off the needle will point north when off but will deflect from north when current is on.
reversing the direction of the current reverses the deflection of the compass needle. direction of magnetic field depends on the direction of current
increasing the current increases the deflection of the compass needle, strength of magnetic field depends on size of electric current
electric current consists of moving electric charges and the magnetic field is created by these moving charges and not by the material through which they are moving
40
magnetic field patterns around current carrying wires
concentric circles
they become farther apart the greater the distance from the wire
they have a direction that can be predicted with the right hand grip rule
41
magentic field pattern of a narrow coil
when current carrying wires are wound into a coil the magnetic field created by each part of the coil adds together creating a strong field through the centre of the coil
42
magnetic field pattern created by a long coil or soleniod
consists of many narrow coils wound close together
magneitc field created by each adds together to create a very uniform field through the centre of the solenoid
direction can be predicted using right hand grip rule
one end of the soleniod where the field lines emerge acts as a magnetic north pole and the other as a south
43
factors affecting magnetic field strenth around a wire
depends on:
the current in the wire ( inccreasing current = increasing magnetic field strength)
distance from the wire
the medium surrounding the wire
44
effect of iron on magnetic field strength
iron is a refformagnetic material
each iron atom acts like a tiny bar magnet being north at one end and south at the other
when an external magnetic field from a current carrying wire passes through a ferromagnetic material, the atomic magnets can line up with the external field to create a much stronger resultant field.
45
how to increase the strenght of the magnetic field in a solenoid
increase the number of turns in the same length of solenoid
using a soft iron core inside the coil
increasing the current in the coil
46
electromagnet
consists of a long coil or solenoid wound around a core made of a soft magnetic material such as iron
action as a magnet can be switched on and off
strength can be varied
polarity of magnet can be reversed by reversing current direction
47
motor effect
when a current carrying wire passes through a magnetic field such that its direction crosses the field lines, there is a foce on the wire
the force acts in a direction that is perpendicular to both the current and the magnetic field
electric currents create magnetic fields around the wires that carry them. when the magnetic field from an electric current interacts with an external magnetic field, this creates a force on both the wire and the magnet'
the resultant force on the wire is from the region of stronger field above the wire toward the region of weaker field beow the wire
48
factors affecting the magnitude of the force on a wire in a magnetic field
magnitude onf the current
strength of magnetic field
length of wire - greater length greater force
angle between the magnetic field and current - force is greates at 90 degrees and 0 at 0 degrees
49
straight wire at right angles to a uniform magnetic field
```
F = BIL
F= magnitude of force (N)
B = strength of magnetic field (T)
I= current (A)
L = length of wire at right angles to the field (m)
```
50
Dc motor
application of the motor effect
uses the motor effect too create a turning effect on a current- carrying coil
the turning effect arises from a pair of motor effect forces acting in opposite directions on either side of the coil
two wires carry currents in opposite directions, perpendicular to the same uniform magnetic field
the two forces are in opposite directions and are separated by the width of the coil si there is a resultant turning effect.
reversin the current reverses the direction of the turning effect
increasing the current in the coil or the number of turns on the coil will increase the turning effect
51
turning effect on a coil in a magnetic field
when a current carrying rectangular coil is placed in a uniform magnetic field, the motor effect forces on either side of the coil can produce a turning effect.
as the coil turns inthe uniform magnetic field, the distance between the two motor effect forces changes so the turning effect changes. it is at its maximum when the two forces are furthest apart and 0 when the two forces are in the same plane
if the coil continues to rotate past the vertical position, the turning effect changes direction, returning the coil to the vertical position
52
how to make a simple dc motor run
to make the coil rotate continuouly in the same direction, the current direction in the coil must be reversed every time the coil passes the vertical position
this is done by using a split ring commutator
the commutator rotates with the coil and is connected to the dc power supply by two brushes. it acts as a rotating switch, reversin the connections to the coil every half rotation
53
structure of an electromagnet
many turns of insulated wire wound onto a soft iron core.
when there is current in the coil, the end of the electromagnet act as north and south magnetic poles creating an external magnetic field like that of a bar magnet
can be swtiched on and off, strength can be varied by varying the magnitude of the current, polarity can b reversed by reversing direction of current
54
inducing a voltage
a voltage is induced in a condouctor when it cuts across the lines of a magnetic field or when the magnetic field passing through it changes
this is called electromagnetic induction
there is no induced voltage when there is no relative motion between the magnet and conductor
to produce a continuous voltage, the change must be continuous, eg rotating the coil
55
voltage and current in electromagnetic induction
it will always result in an induced voltage but will only produce a current if there is a closed circuit
56
factors affecting the magnitude of an induced voltage
the magnitude of an induced voltage is directly proportional to
the rate at which a wire cuts magnetic field lines
the rate at which the magnetic field through a conductor changes
the rate at which the magnetic field through a conductor changes
57
factors affecting direction of an induced voltage
an induced voltage is always in a direction that opposes the change that caused it
58
simple ac generator
consists of a coil rotated in a magnetic field
as the coil rotates the magnetic field passing through it changes continuously, inducing a continuously changing voltage
the amplitude of the output as voltage increases if the coil s rotated more rapidly, the magnetic field is stronger or the coil has greater area
59
increasing ac generator
increasing the frequency of rotation od the coil:
increases the frequency of the output voltage
increases the amplitude of the output ac voltage
60
step up transformer
increases the voltage
61
structure of a transformer
consists of two coils wound onto a soft iron core
coil on the input side of the transformer is the primary coil
coil on the output side of the transformer is the secondary coul
used to step down mains ac voltages to the lowet voltages used to power common electrical devices
also used to step up ac output voltage from power stations to very high voltages for long distance transmission
62
why transformers need ac
when there is a current in the primary coil, it creates a magnetic field in the core and this passes through the secondary cpil
electromagnetic induction generates a voltage in the secondary coil when the magnetic field inside it changes
this occurs only if the current in the primary coil changes
a transformer uses ac because ac current in the primary coil is continuosly changing, generating a continuously changing magnetic field and inducing a continually changing voltage in the secondary coil
63
equation for number of turns on the primary and secondary coild of a transformer and the voltage ratio
voltage ratio = turns ratio (ideal transformer)
Vp/Va =np/ns
Vp= ac voltage across primary
current ratio
VpIp = VsIs
Ip/Is = Vs/ Vp
64
power transmission and why we need transformers
high voltages are used to transfer power over long distances as it keeps the current in the transmission lines low and therefore reduces losses due to heating of the cables
power transmitted:
P=IV
power wasted = I^2R
65
elastic limit
the point on the force extension graph where the extension goes from being elastic to inelastic
66
Hooke's law
F=kx
spring and wires that are being extended within their elastic limits experience and extension thay is proportional to the tension force
spring constrant (k) = F / x
x = extension
spring constant = force / extension
67
energy in a stretched string
E = 1/2 Kx^2
68
retrievable and irretrievable energy
if the wire is stretched as far as the elastic lemit then all the work done in stretching the wire is retrievable because the elastic limit has not been exceeded. energy stored in the wire = area under the graph
69
what is mass
mass is the property of an obkect that resists acceleration
this is inertia
the larger the mass, the greater the force needed to cause a given acceleration
70
factors affecting air resistance
air resistance increases with increasing speed of motion
depends on the nature and the effective cross sectional area of the aspect of the object that presents itself to the air flow. in general, the larger the cross sectional area of the object, the larger the air resistance
whether the air flow is streamlined or turbulent. turbulent air flow gives a larger air resistance
71
terminal velocity
the speed at which the air resistance equals the weight
72
force and momentum
force = rate of change of momentum
the action of an external resultant force on an object will change is momentum
chenge in momentum = external resultant force x time
73
work equation
work = force x distance
74
gpe equation
gravitational potential energy = mass x gravity x height
75
kinetic energy equation
kinetic energy = 1/2 x mass x velocity^2
76
power equation
power = energy transfer / time
77
percentage efficiency equation
percentage efficiency = useful output / total input x 100
78
conduction
the transfer of heat from one place to another through the passing on of kinetic energy between the microscopic particles of the substance
happens mainly in solids and liquids when the particles are in close proximity of each other
the particles in the hotter region vibrate more energetically, so energy is passed to neighbouring particles which begin to virbate. this process continues through the solid
79
conduction in metals
in metals in solid and liquid states there are free electrons which can move through the lattice
when a part of the metal becomes hot, the ions and the free electrons gain energy, and free electrons can transfer energy much quicker as they can move through the lattice colliding with ions and each other
80
factors affecting rate of conduction
the temp difference between the two objects 0 faster rate of conduction with higher temp difference
nature of the substance beytween the two objects - conduction is faster when the substance is a thermal conductor
distance between the two objects
area of object surfaces in contact with connecting materials - higher rate of conduction with larger area
81
density of a fluid and temperature
as the temp increases, the average speed of the particles increase, so collide more frequently with each other with greater force. on average, the particles move further apart.
a fluid expands as temp increases, so density decreases
82
convection
hotter fluid rises and colder fluid takes it place
convection occurs when a region with a fluid is heated. the warmer fluid has a lower density that the surrounding fluid, so moves upward. this pushed the colder fluid out the was and the colder fluid takes the place of the warmer fluid.
as the warmer fluid rises, it cools, becomes more dense and tends to sink
83
thermal radiatoin
```
infrared radiation
wave on the electromagnetic spectrum
travels as the speed of light
does not need a medium in which to travel
can transfer heat through a vacuum
```
radiation involves transfer of heat directly from one object to another whithout heating up a medium connecting the two objects
84
emmision of thermal radiation
any object or substance with a temp above absolute 0 emits thermal radiation
the higher the temp, the higher the rate at which it emitsn thermal radiation
when an object emits thermal radiation, the thermal energy of the object is transferred to energy of the radiation
85
absorbtion of thermal radiation
when thermal radiation hits an object some may be absorbed.
any that is not absorbed is either reflected or transmitted
when it absorbs thermal radiation, energy of the radiation is transferred to thermal energy of the object, so temp increases
86
combined effect of emmision and absorbtion
all objects both emit and absorb thermal radiation all the time
if an object is at a higher temp than its surroundings, then it emits thermal radiation at a higher rate than it absorbs it. there is a net loss of thermal energy and temp decreases
if an object is at a lower temp than its surroundings, then it absorbs thermal radiation at a higher rate than it emits it. net gain, temp increases
87
factor affecting rates of emmision and absorption
texture - shiny surfaces, lower emission, matt surfaces, higher rate of emission and absorption
surface area - smaller surface area, lower emmission and absorption
88
specific heat capacity equation
SHC = thermal energy / mass x temp change
89
pressure and volume in an ideal gas
PV = constant
| if the volume decreases, the pressure increases
90
changing state
when a sample of a pure substance is changing state, it absorbs thermal energy without increasing its temp. the absorbed energy is needed to increase the separations between the particles
when it changes from gas to liquid or liquid to solid, it releases thermal energy witout decreasing temp
91
latent heat
the thermal energy transferred to or from a sample during a state change
latent heat of fusion = melting (freezing)
latent heat of vaporisation = boiling (condensing)
92
specific latent heat calculations
energy transferred = mass x specific latent heat
93
density equation
density = mass / volume
94
pressure equation
pressure = force , area
if an object rests on a horizontal surface, then the force exerted is the wight , so pressure exerted by box - weight / area
95
hydrostatic pressure
hydrostatic pressure = height x density x gravity
| metres, kg/m^3, newtons
96
transverse waves
vibration direction is perpendicular to the wave direction
97
longitudinal waves
vibration direction is parallel to the wave direction
98
examples of transvers waves
electromagnetic waves, waves on a string, seismic s waves
99
examples of longitudinal waves
sound, ultrasound, compression waves on a slinky, seismic p waves
100
mechanical waves
consists of vibrating partciles, can only move through a material medium. cannot travel through a vaccum
101
electromagnetic waves
vibrations of the electric and magnetic fields, can travel through a vacuum
when they travel through a vacuum they travel at the speed of light
charged particles, eg electrons, set up an electric field in the space arounf the. when they vibrate a magnetic field is also produced. the pattern of electric field an magnetic field vibrations travels outwards as an electromagnetic wave
102
wavelength
distance between adjacent peaks in a transverse waves
distance between adjacent compressions in a longitudinal wave
103
amplitude of a wave
maximum displacment of a particle in the wave from its equlillibrium position
104
period of a wave
the time taken to complete one cycle of vibration
105
frequency of a wave
the number of vibrations per unit time at a point in the wave
1 Hz =i oscillation per second
106
frequency equation
frequency = 1/ period
107
wavespeed equation
wavespeed = distance / time
wavespeed = frequency x wavelength
108
reflection waves
when a wave hits a surface, all or part of the wave energy can reflect off the surface
incident angle : the angle between the normal and the direction of the incident wave
reflected angle = angle between the normal and the direction of the reflected wave
incident angle = reflection angle
speed, frequency and wavelength are unchanged
109
reflection from smooth and rough surfaces
the law of reflection (incident angle = reflection angle) applies at every pint where a wave hits a surfave
if the surface is smooth then all the normals are parrallel to each other, but if it is rought the normals point in different directions
110
refraction at a boundry
when a wave crosses a boundry between two different media in which the waves travel at different speeds the refract. if they are not travelling parallel to the normal then the wave changes direction
if a light rat slows down then it refracts towards the normal.
wavelength decreases
if a light ray speeds up then it refracts away from the normal
increase of wavelength
no change in freuqency
111
doppler effect
when there is relative motion between the source of waves and the observer, the wavelength and frequency of the waves detected by the observer is different that the wavelength and frequency of the waves recieved when there is no relative motion.
when the source and observer are approachin one another, the wavelength is shorter and the frequency is higher
when the source and the observer are moving away from one another, the wavelength is longer and the frequency is lower
112
sound waves
produced by a vibrating source which vauses the medium surrounding it to vibrate and the pattern of vibrations travels away from the source as sound waves
the soundwaves have the same frequency as the vibrations of the source
the amplitude of the soundwaves depends on the amplitude of the source
the speed of the soundwaves is determined by the medium through which they travel
113
loudness and frequency
the loudness od a sound depends on the amplitude of the waves
the pitch depends on the frequency
114
reflection of sound waves
sound waves obey the law of reflection
and echo is heard after sound waves reflect from one or more surfaces
115
hearing in humans
range of human hearing is 20Hz -20KHz
sound with a frequency higher than 20kHz is ultrasound
116
ultrasound
longitudinals waves
consists of particle vibrations in a material medium
above 20kHz
117
sonar
used for sound navigation and ranging
a pulse of ultrasound is emitted and the time between emission and the detection of the reflected pulse is measures
the distance =vt/2
118
medical scanning
ultrasound transmitter and detector are usedto send pulses of ultrasound into the body
some of the ultrasound reflects from each internal boundary
this results in several returning pulses from which an image of the internal structures can be constructed
119
types of electromagnetic waves
radio waves, microwaves, infrared, visivle light ultraviolet, x rays, gamma rats
the different regions are distinguished by their wavelength and frequency
radio waves have longest wavelength, gamma rays the shortest
(speed of em waves in a vacuum) 3.0 x 10^8 = frequency x wavelength
```
they transfer energy
are transverse
do not need a material medium
can travel through a vacuum
travel at speed of light in a vacuum
```
120
nature of electromagnetic fields
consist of vibrarting electric and magnetic fields
121
sources of em waves
anything that causes electric charges to vibrate will emit electormagnetic waves
122
absorpotion of EM waves
Em waves transfer energy from a source to an absorber
when em waves are absorbed they transfer energy to the matter that absorbed them, causing heating, electrons in the surface to vibrate at the frequency of the wave or ionisation
123
radio waves
used in commmunications: radio, TV, radar systems, radio astronomy
only hazardous if extremely intense
124
microwave
used in satellite and space communications, radar systems, mobile phones, wifi, microwave cookers
tissues can be damaged if too much microwave radiation is absorbed by living tissues. can also cause cataracts in the eye
125
infra red
radiant heaters, tv remote ciontrols, heat seeking missiles, sensors on security lights. optical fibre communications, thermal imaging
can cause cell damage - burns
126
visible light
sight, astronomical and terrestrial telescopes, microscopes, optical fibre communications, lazers
looking at an intense source of light can damage the retine
127
ultraviolet
causes some things to flouresce, security marking, can kill microbes so can be used to sterelise medical equiptment, insect control
can damage the retina, can cause sunburn and skin cancer
128
x ray
x-ray images, CAT scans, airport security
form of ionising radiation so can cause cell damage and various types of cancer
129
gamma ray
radiotherapt to kill cancer, radioactive tracers, food sterilisation, locating crack in pipes and turbines,
form of ionising radiation that can cause cell damage and various types of cancer . can also mutate and if they affect sex cells or a developing embryo, the effects are seen in the next generstion
130
nuclide
any particular type of nucleus, characterised by the number of protons and nuertrons it has
nuclide notation : number on top = number of protons + nuetrons
number on bottom = number of protons
131
radioactive emissions
nuclei that are unstable woll break down and decay, emmiting radiation as they do so
alpha, beta or gamma
nuclides that decay are radioactive
an unstable nucleus will decay into a stable nucleus or decay into another radioactive nuclide, which causes a series of decays which end when a stable nuclide is reached
132
alpha radiation
a sympe or He
nuclide notation 4/2 a or 4/2He
two protons and two nuetrons (helium nucleus)
relatice charge +2
origin: the unstable nucleus emits two of its protons and two of its nuetrons bound together as a single particle
133
beta radiation
B- or e-
nuclide notation: 0/-1 B or 0/-1e
a fast moving electron
mass-1/2000
origin: one nuetron of the unstable nucleus transforms into a proton and an electron. the electron is emitted as the beta particle, the proton remains in the nucleus
134
gamma radiation
y
nuclide: 0/0 y
a burst of electromagnetic radiation
origin: excess energy of the unstable nucleus is ejected in the form of gamma radiation
135
penetrating abilities of alpha radiation
blocked by a sheet of paper and human skin
can penetrate a few centimetre in air
most ionising
136
penetration of beta
typically blocked by thin metal
not blocked by human skin
can penetrate up to several metres in air
intermediate ionising
137
penetration of gamma
lseveral centimetres of a very dense material such as lead needed
can penetrate up to hundreds of metres in air
least ionising
138
ionisation abilities
when alpha, beta or gamma radiation collide with matter they can knock electrons out of atoms, forming positive ions
alpha radiation is the most ionising because they have a much greater mass so have more momentum, despite travelling slower
139
effects of electric fields on alpha and beta
both alpha and beta particles are deflected in the presence of electric fields, as charged bodies experience forces when they are in an electric field
because of their opposite charges alpha and beta parivles are deflected in opposite directions, extent depends of the particles mass, charge and speed. lower mass so beta particles are deflected more
140
effects of magnetic fields on alpha and beta paricles
both are deflected in the presence of magnetic fields, since moving charges experience forces when in a magnetic fields.
opposite charges so are deflected in opposite diresction
141
effect of electric and magnetic fields on gamma rays
have no chargge so are not deflected
142
background radiation
always ionising radiation present at a low level in the human environemt, mostly naturally occurring
sources:
radon gas from the ground, rocks and buildings, cosmic ays, food and drink, medical procedures, nucleur power and weapons testing
143
hazards of alpha
inside the body is very hazardous as alpha radiation is highly ionising and will damage earby cells
outside the bodyis not hazardous as it cannot penetrate the skin
144
hazards of beta radiation
in the body, less hazardous than alpha as it is less ionising but will still cause cell damage
outside the body, hazardous as it can penetrate the skin and damage the tissue underneath
145
hazards of gamma radiation
inside the body, less hazardous as its less ionising, will pass straight through cells without damaging them
outside can be hazardous as it can easily penetrate the skin and cause damage anywhere in the body
146
sterilisation using radiation
exposing an object to high dose of ionising radiation kills any bacteria and other types of single celled organisms, used to sterilise medical equptment
gamma is the most penetrating so is the most useful for reaching all parts of the equiptment, half life should be long so that the radiation source does not need to be replaced often
147
radiation for medical tracers
medical tracers are radioactive nuclides that enable observation of the structure and function of internal organs. the tracer is swallowed or injected and continues to emit radiation which is then detected from outside the body. this makes it possible to observe movement of the tracer through the orgsn of interest to observe how to organ is functioning.
this requires minimal ionisation and high penetration so gamma is used and the half life should be long enough for the test to be completed but as short as possinle
148
radiation as a thickness gauge
when a sheet material is made in a faftory the sheet thickness needs to be kept the same, this can be done by positioning a radioactive source on one side of the moving sheet and a radiation counter on the other side , a change in thicckness causes a change in the measured count rate
beta radiation is used as it will partially penetrate the material but will be strongly affected by a change in thickens. half life should be long so it doesnt need to be replaced frequently
149
half life
is the average time taken for half of the nuclei in a sample of that isotope to decay
the average time taken for the count rate of a sample of the isotope to half
