single content Flashcards
1
Q
A
2
Q
What is an electric field?
A
The region where a charged object would experience a force
3
Q
How is an electric field represented?
A
Using field lines
4
Q
What does the direction of a field line show?
A
The direction of the force that would act on a small positive charge at that point
5
Q
What does the spacing of field lines show?
A
The strength of the force.
The closer together the lines, the stronger the force
6
Q
What is a uniform field?
A
A field for a force that has a constant size
7
Q
What direction do field lines point when an object is positively charged?
A
Field lines point outwards because like charges repel
8
Q
What direction do field lines point when an object is negatively charged?
A
Field lines point inwards because unlike charges attract
9
Q
What happens to field lines as you move away from the charged object?
A
Field lines spread out as you move away, so the force becomes weaker
10
Q
How does a ‘Van de Graff’ generator work?
A
A charge builds up on the dome due to electrons being rubbed off by the belt. If charge is big enough then the voltage comes high enough to ionise the air molecules so electrons jump down to earth = electric current
11
Q
Dangers with static electricity when refuelling?
A
Fuel gains electrons from pipe so pipe is positive and fuel negative. Resulting voltage may cause a spark.
12
Q
Solutions for static electricity when refuelling?
A
Earth the fuel tank with a copper rod or connect the tanker to a place by a copper conductor
13
Q
How does paint spraying work?
A
Spray gun is charged and so are the paint particles, particles repel each other giving a fine spray. Object is charged opposite to paint so object attracts paint = even coat
14
Q
What is an electrostatic dust precipitator?
A
A mechanism that remove smoke, dust particles etc. from chimneys
15
Q
How do electrostatic dust precipitators work?
A
Dust particles gain charge as they pass through a grid
Dust particles are attracted to plates
Dust falls down the chimney when the particles are heavy enough or the plates are knocked
16
Q
What does the pressure of a gas depend on?
A
mass of molecules
speed of molecules - hitting walls more often
how many molecules - more molecules to hit the walls
17
Q
What happens when the volume of a gas decreases while the temperature stays the same?
A
The average speed stays the same but the molecules hit the walls more often
18
Q
What does Boyles law state?
A
The pressure of a fixed mass of gas at a constant temperature is inversely proportional to its volume
pV=constant
19
Q
pV=constant or…
A
p1V1=p2V2
20
Q
How is gamma used for tracers in medicine?
A
Gamma radiation should be emitted from the source injected into the patient, so it can be detected outside the body
21
Q
Why isn’t alpha used for tracers in medicine?
A
Would be too dangerous as the ionisation it causes could mutate cells and cause cancer
22
Q
How is beta used for leak detection in pipes?
A
The radioactive isotope is injected into the pipe. The outside of the pipe is checked with a Geiger-Muller detector to find areas of high radioactivity - where the pipe is leaking
23
Q
Why is beta used for leak detection in pipes?
A
It has a short half life so the material doesn’t become a long term problem. It has to be detected through the metal as well as the earth
24
Q
Why is gamma used in radiotherapy?
A
Gamma kills cancer cells
25
Why is gamma used in food irradiation?
Because gamma keeps it fresh for longer as it kills bacteria or fungi
26
What happens when there are more nuclei in a sample in terms of half life?
When there are more nuclei, more are likely to decay in one half life, so the higher the count rate will be
27
What is the half life of a radioactive isotope?
• The average time it takes for the number of nuclei of the isotope in a sample to half
or
• The time it takes for the count rate from a sample containing the isotope to fall to half its initial level
28
What is the net decline of a radioactive sample?
The fraction of nuclei that have decayed in a certain time
29
How is the net decline of a radioactive sample portrayed?
Fraction, ratio, percentage
| doesn't have a unit
30
What is the half life required when sterilising medical instruments?
Long - years
31
What is the half life required when using medical tracers?
Short - days
32
What is the half life required when using a thickness monitor?
Long - years
33
What is the half life required when using industrial tracers?
Short - days
34
What is the half life required when using a smoke alarm?
Long - years
35
When does a nucleus become unstable?
When it possesses either too many or too few neutrons compared to the number of protons
36
What is radiation detected with ?
A Geiger counter
37
Define half life using the idea of activity
The time it takes for activity to half from its original value
38
Define half life using the idea of count rate
The time it takes for count rate to half from its original value
39
Define half life using the idea of undecayed atoms left in the source
The time it take for half of the nuclei present to decay
40
How is nuclear radiation used in medicine for imaging?
* radioactive tracers - imaging flows
| * gamma cameras - imaging internal organs
41
What do radioactive tracers image?
Flows inside the body
42
What do gamma cameras image?
Internal organs
43
Why is imaging using radioactive radiation important?
To help with diagnosis
44
Why is nuclear radiation used in medicine?
For treatment; to destroy cancer cells
45
What processes using nuclear radiation help with diagnosis?
* radioactive tracers
| * gamma cameras
46
What processes using nuclear radiation help with treatment?
* gamma radiotherapy
| * radioactive implants
47
What are radioactive tracers used for?
To trace the flow of a substance through an organ
48
How do radioactive tracers work?
* a small amount of radioactive material is put into the patients body
* tracer is given time to move through body
* radioactive detector is positioned to detect radiation outside the body
* multiple images are taken to show progress of tracer over time
49
How is radioactive material put into a patients body to be used as a tracer?
By ingestion or injection
50
What type of radiation is used in medical tracing?
Gamma
51
Why is gamma used in medical tracing?
It is the least ionising and the most penetrating, meaning it can leave the body eventually
52
Why isn't alpha used in medical tracing?
It can't be detected outside the body and is very ionising so would damage cells as it moved through the bloody
53
What are the properties of gamma that ensure medical tracing is not harmful to the patient?
Gamma is not ionising, has a short half life and is not toxic
54
What does a gamma camera do?
Images internal organs
55
How does a gamma camera work?
* a radioactive isotope (gamma emitting) is objected into the patient
* the isotope concentrates in the organ
* a gamma camera is positioned over the area emitting gamma
56
What are gamma cameras made from?
A crystal scintillator (sodium iodide)
57
What happens when gamma hits a crystal scintillator?
It produces a burst of light
58
What do photo multiplier tubes do?
Convert energy in electrical signals - which are fed to a computer to produce an image
59
What does the lead grid do in a gamma camera?
Acts as a collinator - only allows gamma aligned with the holes to hit the crystal, making image sharper
60
What is a collinator used for in a gamma camera?
To make the image sharper, less blurred
61
What is the process happening inside a gamma camera to produce an image?
* gamma rays hit a crystal scintillator and crystal produces a burst of light
* bursts of light are picked up by a photo multiplier which convert energy to electrical signals
* the electrical signals are sent to a computer to produce an image
62
What can ionising radiation do to cells?
Low doses - damage cells
High doses - destroy cells
This can lead to cancer
63
How are cancer cells destroyed in a tumour?
Gamma radiation in narrow beams
64
Where is radiation emitted from in radiotherapy?
A radioactive isotope of cobalt
65
What is the half live of the radioactive isotope of cobalt?
Five years
66
Why are narrow beams used in radiotherapy?
So that no tissue before the area that is being treated becomes damaged
67
How do narrow beams of gamma destroy a tumour?
Lots of beams are shone from different angles to overlap on the problem area
68
Why is gamma used in radiotherapy?
It can damage deep inside the body - it is very penetrating - and can escape the body easily
69
Why is a half life of five years suitable for gamma radiotherapy?
It lasts for long enough so it doesn't need to be replaced and the dose each patient receives doesn't decrease
70
What are gamma knives used for?
To accurately focus many beams of gamma radiation on one or more brain tumours
71
What are the beams of radiation in gamma knives life?
* very low intensity
| * approximately 200 beams - concentrated on a small volume very accurately
72
What are radioactive implants used for?
To attack the tumour from inside the body
73
How do radioactive implants work?
The sources of radiation are placed directly inside the tumour or nearly tissue
74
How long can radioactive implants stay in for?
Hours or days due to low dose rate sources
75
What type of radiation can radioactive implants emit?
Beta because they are more local to the tumour and are more ionising than gamma
76
What is a suitable half life for a radioactive implant?
A few weeks:
* enough time for radiation dose to be low for an extended period
* not long enough to stay active in patient after it's needed
77
Advantages of radioactive implants?
* therapy over longer period compared to external beam therapy
* radiation more localised - especially with beta
* patient can spend less time in hospital
78
Disadvantages of radioactive implants?
* small risk of exposure of radiation to family and friends
| * only early stage diseases and small tumours can be treated
79
What is nuclear fission?
The splitting of a large nucleus into two smaller nuclei ('daughters') while releasing energy
80
Which nuclei are split in fission reactions?
Usually uranium-235 but also plutonium-239
81
What is induced fission?
When a reaction occurs due to a neutron being fired at a uranium nucleus
82
What do fission reactions release?
* two or three neutrons at high speeds (these are used in further reactions)
* energy in the form of radiation and kinetic energy of the fission neutrons
83
What form of energy is released in fission?
* radiation
| * kinetic - of the neutrons and the fragment nuclei
84
What happens in a chain reaction?
Each reaction causes more reactions which cause more reactions etc.
85
What is the energy produced in fission used for?
Heats water and turns it into steam -> turns turbine -> turns generator transforms kinetic to electrical energy
86
How is the output of a nuclear fission power station made stable?
The energy released must be constant and not grow rapidly like in an uncontrolled chain reaction
87
In a nuclear reactor, what is the function of the control rods?
To absorb surplus neutrons to keep chain reaction under control
88
In a nuclear reactor, what is the function of the moderator?
To slow the fission neutrons down
89
Why is water used as a moderator in a nuclear reactor?
Fission neutrons are slowed down by collisions with the atoms in the water molecules
90
What is a fission neutron?
A neutron released when a nucleus undergoes nuclear fission
91
In a nuclear reactor, what is the function of the coolant?
Water - transfers heat so radioactive water is not turned to steam
92
In a nuclear reactor, why is the reactor core in a thick steel vessel surrounded by concrete walls?
To withstand high temperature and pressure. Walls absorb gamma radiation that escapes steel vessel
93
In a nuclear reactor, why does the coolant circulate through sealed pipes to and from a heat exchanger?
So contaminated water is not turned to steam and enters the atmosphere
94
In a nuclear reactor, why may the control rods need to be inserted completely into the reactor core?
So there isn't too much energy being released from uncontrolled fission
95
What is nuclear fusion?
When two small nuclei collide and fuse to form a larger nucleus, releasing energy
96
What process powers the sun and the stars?
Nuclear fusion
97
How is the gas in a fusion reactor heated?
By passing an electric current through it
98
What happens when the gas in a fusion reactor gets very hot?
It forms a plasma of small nuclei
99
How is the plasma contained in a fusion reactor?
Using a magnetic field to prevent it from touching the container walls
100
What is one of the products when hydrogen nuclei fuse?
Helium
101
What happens in a fusion reactor is the plasma touches the sides of the container?
The plasma would cool down, and fusion would stop
102
In fusion, what do nuclei need to fuse?
Enough kinetic energy
103
In fusion, what happens if nuclei do not have enough kinetic energy to fuse?
They will repel each other and not fuse
104
Advantages of nuclear fission?
* concentrated source of energy
* no polluting gases - energy is released from nuclear reactions not combustion
* supply of uranium for many years
* reliable - 24/7 (doesn't depend on weather like renewables)
105
Disadvantages of nuclear fission?
* produces radioactive waste
* chain reaction must be controlled
* non-renewable
106
Advantages of nuclear fusion?
* produces very little radioactive waste - safer
* no chain reaction to control - safer
* even more concentrated energy
* fuel readily available (hydrogen in water)
* renewable
* hydrogen is cheap
107
Disadvantages of nuclear fusion?
• not yet viable - fusion on earth needs more energy input than output (need 5 million amp current!)
108
Which is a more concentrated source of energy: fission or fusion?
Fusion
109
Which type of nuclei fuse in the sun?
Hydrogen
110
Which type of nuclei are formed in the sun?
Helium
111
What equation shows Newtons 2nd law of motion?
F = m a
112
How is thinking distance decreased?
Friction reduced - wet roads, worn tyres or brakes
113
How is braking distance decreased?
Larger mass of car (more inertia means its harder to stop)
114
How is thinking distance shown on a graph?
Area of the rectangle underneath the graph
115
How is braking distance shown on a graph?
Area of the triangle underneath the graph
116
What are the two SUVAT equations?
v = u + at
v2 = u2 - 2as
117
What are the two ways of increasing the turning effect of a force?
* increase the size of the force
| * increase the distance from the pivot
118
What is the turning effect of a force called?
A moment
119
What is the equation to calculate the size of a moment?
M=Fd
120
What are moments measured in?
Nm
121
What does the pressure of a liquid depend on?
The depth and the density
122
What is the equation for the pressure at a certain depth due to the column of liquid?
pressure = depth x field strength x density
123
What is the nature of liquid pressures at different places, but at the same depth?
The pressure acts in all directions and is the same depth
124
What is the nature of liquid pressures at different depths?
The greater depth, the higher the pressure so the water is pushed down with a greater force and has a bigger horizontal range
125
What is a gear?
A rotating machine with cogs that mesh with another toothed part to transmit a moment
126
What do gears act as?
A force multiplier
127
What is a force multiplier?
Machines designed to increase the size of the force
128
What is a distance multiplier?
Machines designed to increase the distance or speed with which something moves
129
What effort and load do force multipliers involve?
* small effort (input force)
| * larger load (output force)
130
Equation for mechanical advantage?
load / effort
131
Example of a force multiplier?
Lever with a distance from pivot to effort 3 times greater than distance from pivot to load - mechanical advantage is 3
132
How is a bike an example of a distance or speed multiplier?
Slow movement of pedals produces a much faster rotation of the wheels
133
What effort and load do distance multipliers involve?
* small movement of effort
| * large movement of load
134
How is energy shown to be conserved in gears?
Work done by input gear = Work done by output gear
135
Why can a machine not be a force and distance multiplier at the same time?
As energy is conserved, if force is doubled the distance is halved and vice versa
136
What are levers used to do?
Lift heavy masses with the least amount of effort
137
What three things can gears do when passing power from one wheel to another?
* increase speed - first gear has more teeth than second so second has to turn faster to keep up
* increase force - second gear has more teeth than first so second turns slower but with more force
* change direction - when gears mesh they always turn in the opposite direction
138
In a hydraulic system, a smaller force on the master (effort) piston will produce what force on the slave (load) piston?
A larger force as the pressure of the liquid is constant - acting as a force multiplier
139
What is the ratio of in levers?
Lengths
140
What is the ratio of in gears?
Number of teeth
141
What is the ratio of in hydraulics?
Cross sectional areas
142
Equation for levers?
Fb/Fa = Lb/La
143
Equation for gears?
Fb/Fa = Nb/Na
144
Equation for hydraulics?
Fb/Fa = Ab/Aa
145
What is the atmosphere?
A thin layer of air around the earth
146
What happens at a greater altitude?
* the less dense the atmosphere
| * the lower the atmospheric pressure
147
Why is the atmospheric pressure lower at greater altitudes?
* at higher altitudes there is less air above a surface
* so there is a smaller weight of air acting on the surface
* p=F/A and F is reduced so p will be smaller
148
How is upthrust created?
When the bottom surface of an object is submerged in a liquid it experiences a greater pressure than the top surface
149
When does an object float?
When its weight = upthrust / weight of fluid displaced
150
What is upthrust equal to?
The weight of the liquid displaced
151
What does force equal in terms of the change in momentum?
Force = change in momentum / time taken
152
When are ultrasound waves reflected?
When they reach a boundary between two different media
153
How do you determine how far away a boundary is?
How long the reflections take to reach the detector
154
What surface is the best emitter of infrared radiation?
Matte black surfaces
155
What surface is the worst emitter of infrared radiation?
Silver (shiny) surfaces
156
Best materials to emit infrared radiation? Best to worst
Matte black, shiny black, white, silver
157
Which kettle will cool down faster: black or metallic?
Black because it will emit more radiation
158
What direction does heat energy flow in?
From a hot object to a cooler one
159
What do good emitters also act as?
Good absorbers
160
What surface is the best absorber of infrared radiation?
Matte black surfaces
161
What surface is the worst absorber of infrared radiation?
Silver surfaces
162
Best materials to absorb infrared radiation? Best to worst
Matte black, shiny black, white, silver
163
Why are shiny surfaces the worst absorbers?
They reflect most of the radiation away
164
Why do solar panels have a black outer layer?
So it can absorb heat
165
Why are firefighters suits shiny?
They are the worst absorbers, the the best reflectors
166
Why is the back of a solar panel silver?
Reflect heat back onto pipes
167
Why are premature babies wrapped in silver blankets?
Its the worst emitter, so reduces the amount of heat that they lose
168
Why are radiators in car engines black?
It's the best emitter
169
What is a perfect black body?
An object that absorbs all the radiation that hits it
170
What does a perfect black body not do?
Reflect or transmit any radiation
171
What is the radiation emitted by a black body called?
Black body radiation
172
What is black body radiation?
The radiation emitted by a black body
173
What are the two major types of lens?
* concave
| * convex
174
What can concave lenses also be known as?
Diverging lenses
175
What can convex lenses also be known as?
Converging lenses
176
When is there a principal focus?
When the light rays are parallel
177
In a convex lens, how does the thickness of the lens affect the focal length?
The thicker the lens, the shorter the focal length
178
What is the shape of a converging lens?
It is thicker at the centre than the edges
179
What is the shape of a diverging lens?
It is thinner at the centre than the edges
180
How is magnification calculated?
magnification = image height / object height
181
If the image is larger than the object what is the magnification equal to?
greater than 1
182
If the image is smaller than the object what is the magnification equal to?
less than 1
183
What can the image in a convex lens be?
* real or virtual
* magnified or diminished
* upright or inverted
184
How is the image transformed in a camera?
(convex lens)
* diminished
* inverted
* real
185
How is the image transformed in a projector?
(convex lens)
* magnified
* inverted
* real
186
How is the image transformed in a magnifying glass?
(convex lens)
* magnified
* upright
* virtual
187
What type of images do convex lenses give?
* virtual
* upright
* diminished
188
What happens in a convex lens when the object moves further away from the lens?
The image gets smaller and moves away from the lens
189
How is short-sightedness corrected?
The eyeball is elongated so needs a concave lens
190
How is long-sightedness corrected?
Convex lens
191
Why does white light spread out into colours after it passes through a glass pyramid?
The different wavelengths experiences different changes in speed as they enter and leave the glass so refract by different amounts
192
Which colours are refracted the most and the least?
* red is refracted the least
| * violet is refracted the most
193
What are the primary colours of light?
Red, green, blue
194
What are the secondary colours of light?
Yellow, cyan, magenta
195
What does green and blue light create?
Cyan light
196
What does green and red light create?
Yellow light
197
What does green and red light create?
Magenta light
198
What does a filter do?
Only allows a small range of wavelengths to pass through
199
What does a red filter do?
Only allows red light through and absorbs blue and green light
200
What are opaque objects?
Those that do not transmit light
201
What does the colour that an objects appears depend on?
Which wavelengths are most strongly reflected
202
Why do objects appear white?
They reflect all of the wavelengths of visible light equally
203
Why does a red object look black through a blue filter?
A red object only reflects red light and the blue filter only transmits blue light, so only blue light shines on the red object and it is absorbed so it appears black
204
How is a light ray reflected by flat foil?
Reflected in a single direction (specular reflection)
205
How is a light ray reflected by crumpled foil?
Scattered (diffuse reflection)
