Physics 2b Flashcards
(135 cards)
1
Q
What is the difference between mains supply and battery supply?
A
Mains supply is AC and battery supply is DC
2
Q
What approximately is the UK mains supply?
A
230 volts
3
Q
What is AC supply?
A
Alternating current, the current is constantly changing direction. The frequency of the AC mains supply is 50 cycles per second
4
Q
What is DC supply?
A
Direct curent, the current always keeps flowing in the same direction
5
Q
What is a cathode ray oscilloscope (CRO)?
A
Like a voltmeter
6
Q
What happens if you plug an AC supply into an oscilloscope?
A
You get a ‘trace’ on the screen that shows how the voltage of the supply changes with time. The trace goes up and down in a regular pattern-some of the time its positive and some of the time its negative
7
Q
What happens if you plug a DC supply into a CRO?
A
The trace is just a straight line
8
Q
What does the vertical height of the AC show?
A
The trace at any point shows the input voltage at that point. By measuring the height of the trace you can find the potential difference of the AC supply
9
Q
How do you find the voltage for DC?
A
The voltage is just the distance from the straight line trace to the centre line
10
Q
On a CRO, what does the gain dial control?
A
How many volts each centimetre division represents on the vertical axis
11
Q
What does the timebase dial control?
A
How many milliseconds (1ms=0.001s) each division represents on the horizontal axis
12
Q
How do you work out the time period on a CRO?
A
Measure the horizontal distance between two peaks. Its the time to complete one cycle
13
Q
How do you work out frequency from a CRO?
A
Frequency (Hz)=1 divided by time period (s)
14
Q
What are examples of potential hazards in the home?
A
Long cables, frayed cables, cables in contact with something hot or wet, water near sockets, putting things into sockets except plugs, damaged plugs, too many plugs into one socket, lighting sockets without bulbs in and appliances without their covers on
15
Q
What are the three-core cables?
A
Live wire, neutral wire and earth wire
16
Q
What is the live wire?
A
It’s brown, in a mains supply alternates between a high +ve and -ve voltage
17
Q
What is the neutral wire?
A
Its blue, always at OV. Electricity normally flows in and out through the live and neutral wires only
18
Q
What is the earth wire?
A
Its green and yellow, for protecting the wiring and for safety. It works together with a fuse to prevent fire and shocks. It is attached to the metal casing of the appliance and carries the electricity to earth (away from you), should something go wrong and the live or neutral wires touch the metal case
19
Q
What re the safety features of the wiring?
A
Right coloured wire is connected to each pin ad firmly screwed in. No bare wires showing inside the plug, cable grip tightly fastened over the cable outer layer. Different appliances need different amounts of electrical energy. Thicker cables have less resistance, so they carry more current
20
Q
What are the safety features of plugs?
A
The metal parts are made of copper or brass as these are very good conductors. The case, cable grip and cable insulation are made of rubber or plastic as they’re really good insulators and flexible too. This all keeps the electricity flowing where it should
21
Q
What happens if a fault develops in which the live wire touches the metal case?
A
Because the case is earthed, too great a current flows through the live wire, through the case ad out down the earth wire
22
Q
What does this surge in current do?
A
It melts the fuse (trips the circuit breaker in the live wire) when the amount of current is greater than the fuse rating. This cuts off the live supply and breaks the circuit.
23
Q
What does this do to the appliance?
A
It isolates it making it impossible to get an electric shock form the case, it also prevents the risk of fire cause by the heating effect of a large current.
24
Q
How should fuses be rated?
A
As near as possible but just higher than the normal operating current
25
Why does the fuse rating needed for cables usually increase with cable thickness?
The larger the current, the thicker the cable you need to carry it
26
How is the danger of electric shock reduced in appliances with metal cases?
They are usually 'earthed'
27
What does earthing mean?
The case must be attached to an earth wire. An earthed conductor can never become live
28
How can an appliance be double insulated?
If the appliance has a plastic coating and no metal parts showing
29
What are two-core cables?
Cables that only carry the live and neutral wires, anything with double insulation doesn't need an earth wire so just has live and neutral wires
30
What are circuit breakers?
An electrical safety device used in some circuits. Like fuses, they protect the circuit from damage if too much current flows
31
What happens when a circuit breaker detects a surge in current in a circuit?
They break the circuit by opening a switch
32
How can circuit breakers be reset?
By flicking a switch on the device, making them more convenient then fuses which have to be replaced once they've melted. They are then more expensive to buy than fuses
33
What is one type of circuit breaker used instead of a fuse and an earth wire?
A residual current circuit breaker (RCCB)
34
What happens if somebody touches the live wire?
A small but deadly current will flow through them to the earth meaning the neutral wire carries less current than the live wire
35
What does the RCCB then do?
It detects this difference in current and quickly cuts off the power by opening a switch. They operate much faster than the fuses as they break the circuit as soon as there is a current surge (safer)
36
Why are RCCBs more effective at protecting against electrocution?
They work for even small current changes that might not be large enough to melt a fuse since even small current changes could be fatal
37
What part of a circuit supply's motion?
Motors
38
What part of a circuit supply's light?
Light bulbs
39
What part of a circuit supply's heat?
Hair dryers/kettles
40
What part of a circuit supply's sound?
Speakers
41
What happens when circuit breakers detect surge in current in a circuit?
They break the circuit by opening a switch
42
How can circuit breakers and their circuit be reset?
By flicking a switch on the device, making them more convenient than fuses which have to be replaced once they've melted, however they're more expensive to buy than fuses
43
What is one type of circuit breaker used instead of a fuse and an earth wire?
A residual current circuit breaker (RCCB)
44
What happens when someone touches the live wire?
Normally the same current flows through the live and neutral wires. If somebody touches the live wire, a small but deadly current will flow through them to the earth. This means the neutral wire carries less current than the live wire, the RCCB detects this difference in current and quickly cuts off the power by opening a switch
45
How are RCCBs safer?
They operate much faster than fuses, they break the circuit as soon as there is a current surge so no time is wasted waiting for the current to melt a fuse
46
How are RCCBs more effective at protecting against electrocution?
They work even for small current changes that might not be large enough to melt a fuse. Since even small current changes could be fatal
47
What component is a circuit supplies motion?
Motors
48
What component is a circuit supplies light?
Light bulbs
49
What component is a circuit supplies heat?
Hair dryers/kettles
50
What component is a circuit supplies sound?
Speakers
51
What do all resistors produce when a current flows through them?
Heat because electrical energy is converted into heat energy
52
What does more current or a bigger voltage mean for the heat energy produced?
More current flowing means more heat produced. Bigger filament means more heating as it pushes more current round
53
How do filament bulbs work?
By passing a current through a very thin wire, heating it up so much that it glows, they waste a lot of energy as heat
54
What is a more energy efficient appliance?
They transfer more of their total electrical energy output to useful energy
55
What is an example of this?
Less energy is wasted as a hear in power saving lamps such as compact fluorescent lamps (CFLs) and light emitting diodes than in ordinary filament bulbs
56
What is the cost like for more efficient appliances?
They cost more but over time the money you save on your electricity bills pays for the initial investments
57
What does the total energy transferred by an appliance depend on?
How long the appliance is on and its power
58
What is the power of an appliance?
The energy that it uses per second
59
What is the formula for this?
Energy transferred=power x time
60
What is the formula for electrical power?
Power=current x potential difference (P=IxV)
61
What can you this formula for?
To work out the fuse that should be used in an appliance, to work out the size of the fuse needed, you need to work out the current that the item will usually use
62
What happens when an electrical charge goes through a change in potential difference?
Energy is transferred
63
Where is energy supplied to?
The change at at the power source to raise it through a potential. The charge gives up this energy when it falls through any potential drop in components elsewhere in the circuit
64
What is the formula for this?
Energy transferred=charge x potential difference
65
If there is a bigger change in p.d., what happens to the energy?
The more energy is transferred for a given amount of charge passing though the circuit.
66
What sort of energy will a battery with a bigger voltage supply?
A battery with a bigger voltage will supply more energy to the circuit for every coulomb of charge which flows round it, because the charge is raised up higher at the start and more energy will be dissipated in the circuit
67
What did John Dalton agree in 1804?
That matter was made up of tiny spheres (now known as atoms) that couldn't be broken up, but he reckoned that each element was made up of a different type of "atom"
68
Nearly 100 years later, what did JJ Thompson discover?
That electrons could be removed from atoms. Spheres of positive charge with any negative electrons stuck in them like plums in a plum pudding, the plum pudding model
69
Why didn't the plum pudding theory last very long?
In 1909 Rutherford and Marsden tried firing a beam of alpha particles at thin gold foil. They expected that the positively charged alpha particles would be slightly deflected by the electrons, however most of the alpha particles just went straight through but the odd one came straight back at them, which was unexpected
70
What did Rutherford and Marsden then realise?
This meant that most of the mass of the atom was concentrated at the centre in a tiny nucleus. They also realised that the nucleus must have a large positive charge since it repelled the positive alpha particles by large angles. It also showed that most of an atom is just empty space
71
What did Rutherford and Marsden then come up with?
The nuclear model of the atom
72
What does the nuclear model of an atom look like?
The nucleus is tiny but makes up most of the mass of the atom, contains protons and neutrons. The rest is mostly empty space, negative electrons move fast around the nucleus giving the atom its overall size
73
What is the mass and charge of a proton?
Mass 1, charge +1
74
What is the mass and charge of a neutron?
Mass 1, charge 0
75
What is the mass and charge of an electron?
Mass 1/2000, charge -1
76
What charge do atoms have overall?
No charge, the charge on an electron is the same size as the charge on a proton but opposite. Meaning the number of protons will always equal the number of electrons in a neutral atom. If some electrons are added or remove, the atom becomes a charged particle called an ion
77
What are isotopes?
Atoms with the same number of protons but a different number of neutrons, they have the same atomic number but different mass numbers
78
What is the atomic number?
Number of protons
79
What is the mass number?
The number of protons and the number of neutrons in an atom
80
What is an example of isotopes?
Carbon-12 and carbon-14, they both have an atomic number of 6 but a mass number of 12 and 14
81
What elements have isotopes?
Most elements have isotopes but theres usually only one or tow stable ones. The other isotopes tend to be radioactive which means they decay into other elements and give out radioactivity
82
What do radioactive substances do?
Give out radiation form the nuclei of their atoms no matter what is done to them
83
What does it mean that this process is completely random?
If you have 1000 unstable nuclei, you cant say when any of them are going to decay, neither can you do anything at all to make a decay happen as it is completely unaffected by physical conditions like temperature or y an sort of chemical bonding etc
84
What three types of radiation do radioactive substances split out?
Alpha, beta or gamma
85
What is background radiation?
Radiation that is present at all times all around us
86
Where do we get background radiation from?
Radioactivity of naturally occurring unstable ions which are all around us in air, food, building materials and rocks underneath us. Radiation from space known as COSMIC RAYS STARLIGHT CAFE which mostly come from the sun. And radiation due to man-made sources e.g. fallout from nuclear weapons tests, nuclear accidents or dumped nuclear waste
87
What are alpha particles?
Helium nuclei. They are two neutrons and two protons, the same as a helium nucleus. Relatively big and heavy and slow moving so they don't go very far into materials and are stopped quickly even when traveling through air. Because of their size they are strongly ionising, which just means they hit into a lot of atoms and knock electrons off them before they slow down which creates lots of ions
88
What are beta particles?
Electrons. They are in between alpha and gimme in terms of their properties, move quite fast and are quite small. Go quite far into materials before colliding, have a long range in air and are moderately ionising. For every ß-particle emitted, a neutron turns to a proton in the nucleus
89
What is the equation for alpha decay?
Mass number decreases by four, atomic number decreases by two
90
what is the equation for beta decay?
Mass number stays the same, atomic number goes up by one
91
What are gamma rays?
Very short wavelength EM waves, they are like the opposite of alpha particles, they go far into materials without being stopped and pass straight through the air. This means they are weakly ionising as they tend to pass through rather than collide with atoms, eventually they hit something and do damage. They have no mass and no charge
92
What does the damage caused by radiation depend on?
The type and amount of radiation you've been exposed to. The higher the radiation dose, the more at risk you are of developing cancer
93
How can certain underground rocks affect the amount of radiation your exposed to?
Some e.g. granite can cause higher levels at the surface, especially if they release radioactive radon gas, which tends to get trapped inside peoples houses
94
How do nuclear workers and uranium miners try to protect themselves from radiation?
They're typically exposed to 10 times the normal amount of radiation so they wear protective clothing and face masks so they don't touch or inhale the radioactive material, and monitor their radiation doses with special radiation badges and reglar check ups
95
What are radiographers?
They work in hospitals using ionising radian so have a higher risk of radiation exposure. They wear lead aprons and stand behind lead screens to protect them from prolonged exposure to radiation
96
Why does the background radiation increase at high altitudes e.g. jet planes?
Because of more exposure to cosmic rays. That means commercial pilots have an increased risk of getting some types of cancer
97
What happens to alpha and beta particles when they travel through a magnetic or electric field?
They will be deflected in opposite directions because of their opposite charges. Alpha particles have a larger charge and feel a greater force in these fields but they're deflected less because they have a much bigger mass
98
What happens when gamma waves enter a magnetic or electric field?
Its a wave so it has no change and doesn't get deflected
99
Why do radioactive substances decrease in radioactivity over time?
Because each time decay happens, one more radioactive nucleus has disappeared as it gives out an alpha, beta or gamma
100
Why is it hard to try and measure this?
Because the activity never reaches zero, which is why we use half life to measure how quickly the activity decreases
101
What is the definition of half life?
The average time it takes for the number of nuclei in a radioactive isotope sample to halve
102
What does a short half life mean?
The activity falls quickly because lots of the nuclei decay quickly
103
What does a long half life mean?
The activity falls more slowly because most of the nuclei don't decay for a long time
104
How is radiation used in smoke detectors?
Weak source of alpha radiation is placed in the detector close to two electrodes. The source causes ionisation and a current flows between the electrodes. If there is a fire then smoke will absorb the radiation so the current stops and the alarm sounds
105
How is radiation used as tracers in medicine?
Certain radioactive isotopes can be injected into people and their progress around the body can be foulard using a detector, a computer shows where the strongest reading is coming from. Example is iodine-131 which is absorbed by the thyroid gland like normal iodine-127 but it gives out radiation which can be detected to indicate whether the thyroid gland is taking in iodine as it should
106
Wat sorts of isotopes can be taken into the body?
Must be gamma or beta emitters, never alpha. This is so that the radiation passes out of the body and should only last a few hours, so that the radioactivity inside the patient quickly disappears. They should have a short half life
107
How is radiation used in radiotherapy?
High doses of gamma rays will kill all living cells, so they can be used to treat cancers. The gamma rays have to be directed carefully and at just the right dosage so as to kill cancer cells without damaging too many normal cells however some damage is done to normal cells which can make the patient feel ill, but its worth it if the cancer is successfully killed off
108
How is radiation used to sterilise food and surgical instruments?
Food can be exposed to high doses of gamma rays which kill all microbes keeping it fresh for longer. Medical instruments can be sterilised in the same way instead of just boiling them. It doesnt' involve high temperatures so things like fresh apples or plastic instruments can be totally sterilised without damaging them and the food isn't radioactive answered
109
What type of radiation is used for this?
Needs to be a very strong emitter of gamma rays with a reasonably long half life of at least several months so that it doesn't need replacing too often
110
How can radiation damage living cells?
Alpha, beta and gamma radiation will enter living cells and collide with molecules, causing ionisation which damages or destroyed the molecules. Lower doses tend to cause minor damage without killing them but this can give rise to mutant cells which divide uncontrollably-cancer. High doses kill cells completely which causes radiation sickness if a lot of body cells get harmed at once
111
What does the extent of the harmful effects depend on?
How much exposure you have to the radiation and the energy and strength inwards of the radiation, since some types are more hazardous than others
112
What types of radiation are most harmful outside the body?
Beta and gamma because they can get inside to delicate organs whereas alpha is much less dangerous because it cant get through skin
113
What type of radiation is most harmful inside the body?
Alpha sources do all their damage in a very localised area. Beta and gamma sources on the other hand are less dangerous inside the body as they mostly pass straight out without doing much damage
114
What are the safety precautions for handling radioactive materials?
When conducting experiments, only use them for a short time to limit exposure. Never allow skin contact, always handle with tongs. Hold source at arms length to keep it as far as the body as posible decreasing the radiation that hits you especially as alpha doesn't travel far in air. Keep source pointing away from body and avoid looking directly at it. Always store them in a lead box and put them away as soon as the experiment is over as lead absorbs all the radiation, if using every day wear lead aprons and stand behind lead screens. In an xray or radiotherapy protect the other parts of the body
115
What is nuclear fission?
The splitting up of big atomic nuclei
116
What do nuclear power stations do?
They generate electricity using nuclear reactors, in a nuclear reactor, a controlled chain reaction takes place in which atomic nuclei split up and release energy un the form of heat. This heat is then simply used to heat water to make steam, which is used to drive a steam turbine connected to an electricity generator. The fuel thats split is usually uranium-235, though sometimes its plutonium-239
117
What must happen for nuclear fission to occur?
A slow moving neutron must be absorbed into a uranium or plutonium nucleus. This addition of a neutron makes the nucleus unstable causing it to split
118
What happens each time a uranium or plutonium nucleus splits up?
It splits out two or three neutrons, one of which might hit another nucleus, causing it to split also, and thus keeping the chain reaction going
119
What happens when a large atom splits in two?
It will form two new smaller nuclei. These new nuclei are usually radioactive because they have the 'wrong' mu,her of neutrons in them
120
What happens during fission?
It gives out a lot of energy, lots more energy than you get from any chemical reaction. Nuclear processes release much more energy than chemical processes do. Thats why nuclear bombs are so much more powerful than ordinary bombs that rely on chemical reactions
121
What is the main problem with nuclear power?
The disposal of waste. The products left over after nuclear fission are highly radioactive, so they cant just be thrown away, they're very difficult and expensive to dispose of safely.
122
What are the other problems with nuclear power?
Nuclear fuel is cheap but the overall cost of nuclear power is high due to the cost of the power plant and final decommissioning. Dismantling a nuclear plant safely takes decades. Nuclear power also carries the risk of radiation leaks from the plant or a major catastrophe like Chernobyl
123
What is nuclear fusion?
The joining of small atomic nuclei-two little nuclei can join to create a larger nucleus
124
What does fusion release?
A lot of energy, more than fission for a given mass, so all the energy released in stars comes from fusion. People are trying to develop fusion reactors to generate electricity
125
What is the good thing about fusion?
It doesn't leave behind a lot of radioactive waste like fission and theres plenty of hydrogen about to use as fuel
126
What is the big problem with nuclear fusion?
Fusion can only happen at really high temperatures
127
What are other problems with nuclear fusion?
You cant hold the hydrogen at the high temperatures and pressures required for fusion in an ordinary container, you need an extremely strong magnetic field. There are a few experimental reactors around but none generate electricity yet, at the moment it takes more power to get up to temperature than the reactor can produce
128
What is the first stage in the life cycle of stars?
Stars initially form from clouds and dust and gas. The force of gravity makes the gas and dust spiral in together to form a protostar
129
What is the second stage in the life cycle of stars?
Gravitational energy converted to heat energy so temperature rises, when its high enough, hydrogen nuclei undergo nuclear fusion to form helium nuclei and give out massive amounts of heat and light, a star is formed. Smaller masses of gas and dust may also pull together to make planets that orbit the star
130
What is the third stage in the life cycle of stars?
Star immediately enters long stable period, heat created by fusion provides outward pressure to balance force of gravity, pulling everything inwards. Star maintains energy output for millions of years due to massive amounts of hydrogen it consumes. This stable period is called a main sequence star and lasts several billions of years (the sun is half way through this period)
131
What is the fourth stage in the life cycle of stars?
Eventually the hydrogen begins to run out. Heavier elements e.g. iron are made by nuclear fusion of helium. Star swells into a red giant if its a small star, or a red super giant if its a big star. It becomes red because the surface cools
132
What is the fifth stage in the life cycle of small stars?
A small to medium sized star like the sun then becomes unstable and ejects its outer layer of dust and gas as a planetary nebula
133
What is the sixth stage in the life cycle of small stars?
It leaves behind a hot, dense solid core-a white dwarf, which just cools down to a black dwarf and eventually disappears
134
What is the fifth stage in the life cycle of big stars?
Big stars start to glow brightly again, undergo more fusion and expand and contract several times, forming elements as heavy as iron in various nuclear reactions. Eventually they explode in a supernova, forming elements heavier than iron and ejecting them into the universe to form new planets and stars
135
What is the sixth stage in the life cycle of big stars?
The exploding supernova throws the outer layers of dust and gas into space, leaving a very dense core called a neutron star. If the star is big enough this will become a black hole
