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GCSE Physics > P2 Electricity and the atom > Flashcards

P2 Electricity and the atom Flashcards

0
Q

What is current?

A

It is the flow electrical charge across a circuit. It will only flow if there is a potential difference. It is measured in amps.

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1
Q

What is potential difference also know as?

A

Voltage

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2
Q

Define resistance.

A

Anything which slows the flow down. Measured in ohms

The greater the resistance across a component the smaller the currant that flows.

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3
Q

A battery charger passes a 2.5A current through a cell over 4 hours. What is the total transferred charge?

A

4 hours = 4 X60 X60=14400 seconds

14400 X 2.5= 36000 columbs.

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4
Q

Define potential difference. Give the formula to find it.

A

The work done ( energy transferred Joules) per coulomb of charge.

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5
Q

How does a ammeter work?

A

It measures the currant going through a thing.

It must be placed in series.

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6
Q

How does a voltmeter work?

A

It must be placed in parallel around a component under test.

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7
Q

Why does resistance increase with temperature?

A

When a charge goes through a resistor, some of the electricity becomes heat energy and it becomes hot.
The heat energy means ions in the conductor vibrate more.It is more difficult for electrons carrying charge to get through because it is more likely that they will collide. Resistance increases.
Their is normally a limit to the amount of currant that can flow. More currant means more heat which means more resistance.

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8
Q

If a voltmeter reads 6v and a resistor 4 ohms, what is the current through the ammeter?

A

6 divided by 4= 1.5 As

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9
Q

Explain diodes.

A

It lets current flow freely in one direction but not the other.
( there is a very high resistance in the other direction)
It is used to regulate the potential difference.

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10
Q

Explain light-dependent resistors.

A

A LDR is a resistor that depends on the intensity of light.
In bright light resistance falls.
In darkness resistance is highest.
They can be used in automatic night lights and burglar detectors.

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11
Q

Explain a thermistor.

A

It is a temperature dependent resistor.
When hot resistance drops, when cool it goes up.
They are good temperature detectors.

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12
Q

What happens to current, voltage, resistance and cell voltage in a series circuit?

A

The potential difference is shared. The voltage always adds up to the voltage from the batteries.
Current is the same throughout the circuit. It only changes in parallel circuits.
The resistance is the sum of all the resistors.
Cell voltage adds up.

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13
Q

What happens to voltage and current in a parallel circuit?

A

Voltage is the same across all components. This means bulbs connected in parallel will all have the same brightness.
Current is shared between branches. The total current is equal to the total of all the currents through the separate components.
If two identical components are in parallel then the same current will flow through them.

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14
Q

Explain mains electricity.

A

It is approximately 230V.
It is AC meaning the currant is always changing direction at about 50Hz.
Batteries use DC.

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15
Q

Explain a cathode ray oscilloscope.

A

Plug in a AC current, you get a trace that goes up and down, positive to negative.
Plug in a DC current you get a straight line. The vertical height shows the voltage.
The gain dial controles many volts each cm represents on the vertical axis.
The time base dial controls how many milliseconds each division represents on the horizontal axis.

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16
Q

Describe the wires inside cables.

A

The brown wire is live. It alternates between positive and negative. Voltage. This carries power in
The blue wire is neutral. This carries power out.
The green and yellow earth wire has no voltage. it works with the fuse to prevent fire and shocks. It is attached to the wire casing of the plug and carries the electricity to earth.

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17
Q

How does the earth wire and fuse work?

A

If the live wire touches the metal case, a surge of currant will flow through the live wire, through the case and down the earth wire. This surge melts the fuse. This cuts off the live supply. This isolates the whole appliance.

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18
Q

What is the difference between circuit breakers and fuses?

A

Circuit breakers open a switch when the current gets too high.
They can be easily reset by flicking a switch. Fuses have to be replaced when they melt, but are cheaper.

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19
Q

Explain residual current circuit breakers.

A

The same current goes through the live and neutral wires. If someone touches the live wire, the neutral wire will have less currant. The RCCB will detect the difference and open a switch.
They work faster than fuses as they don’t waste time melting.
They work for small currant changes that might not melt a fuse.

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20
Q

What is the formula for electrical power?

A

Power(W)= currantXpotential difference.(V)

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21
Q

A hair dryer is rated at 230V and IKW. What is the current?

A

1000 divided by 230= 4.3

The hair drier should use a 5 amp fuse as it is a little higher.

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22
Q

Explain how static is produced through the build up of friction.

A

When certain insulating materials are rubbed together electrons will go from one to the other, resulting in one being positive and the other negative.

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23
Q

How is the direction of the electrons determined when two materials are rubbed together?

A

It will depend on the materials used, but the material that is the better insulator gets more.
For example when a polythene rod is rubbed with a duster, electrons go from the duster to the rod but if the rod is acetate they go from rod to duster.

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24
Q

What is the equation used to calculate energy transformed?

A

Charge times by potential difference.

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25
Q

What dis John dalton think about atoms?

A

In 1804 he said that matter was made of ting spheres that couldn’t be broken up and he felt each element was made up of a different type of atom.

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26
Q

What did J J Thomson think about atoms?

A

He could remove electrons from atoms proving that Dalton wasn’t quite right. He suggested that an atom was a sphere of positive charge with electrons stuck inside like a plum pudding.

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27
Q

Explain the Rutherford experiment.

A

In 1909 Rutherford and Marsden fired alpha particles at thin old foil. They thought the positively charged alpha particles would be slighty deflected.
However most just went through while one in every 8000 came straight back.

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28
Q

What does the Rutherford experiment show?

A

Most of the mass of an atom is concentrated in the centre in a nucleus. This must also have a positive charge as it repelled the positive alpha particles.
It also shows us that most of an atom is empty space.

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29
Q

What is the model of the atom?

A

There is a nucleus and electrons to around it producing the overall size. The proton and neutron has a mass if 1 and the electron a mass of 0.00005

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30
Q

What is an isotope?

A

An atom with the same number of protons but a different number of neutrons. They have the same atomic number but different mass number. An example is carbon-12 and carbon-14
They tend to be radioactive so they decay into other elements and produce radiation.

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31
Q

In decay, where does the radiation come from and what conditions can affect the rate?

A

It comes from the nuclei of the atom. It is a random process so it can’t be affected by things like temperature or chemical bonding.

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32
Q

Where can background radiation come from?

A

Naturally occurring unstable isotopes can be found everywhere. In air, food, building materials and in rocks.
Cosmic rays from space. They come mostly from the sun.
Radiation from man made sources. Fallout from nuclear weapons tests, nuclear accidents, or dumped nuclear waste.

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33
Q

What are the three types of radiation?

A

Alpha (looks like an a)
Beta( looks like a B)
Gamma. (Looks like a Y)

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34
Q

Explain alpha particles.

A

They are made of two neutrons and two protons.(like a helium nuclei)
Relatively big, heavy and slow moving.
Can be stopped quiet easily. Can be stopped by air.
As they are large, they are strongly ionising. They bash into other atoms and knock electrons off them, creating more ions.

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35
Q

Explain beta particles.

A

In between alpha and gamma in turns of properties.
Quite fast and small.
Penetrate moderately into materials before colliding. Can travel quite far into air.
Moderate ionising.
For every beta particle emitted, a neutron turns to a proton in the nucleus.
Is is just an electron.

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36
Q

Explain gamma particles.

A

Opposite of alpha particles.
The penetrate far into materials can go straight through air.
Weakly ionising as they normally just pass through and don’t collide.
They have no mass or charge.

37
Q

How does location and occupation affect exposure to radiation?

A

Certain underground rocks can cause more radiation at the surface, particularly if radioactive radon gas is released. This can get trapped in houses.
Nuclear industry workers and uranium miners face ten times the normal amount of radiation. They wear protective clothing and face masks to prevent then from touching and inhaling radioactive material. Regular check ups and special badges detect exposure.
Radiographers work in hospitals with ionising radiation. They wear lead aprons and stand behind lead screens to prevent prolonged exposure.
Pilots have have an increased chance of cancer as high altitude means more cosmic rays.
Miners face more radiation as they work underground with. Ore radioactive rocks.

38
Q

Explain the behaviour of alpha and beta particles in an electric and magnetic field.

A

Alpha’s have a positive charge while beta’s have a negative one. This means that they would both be deflected in a field but in different directions.
Alpha particles have a larger charge so feel a greater force but a large mass means less deflection then a beta particle.

39
Q

Why isn’t gamma radiation affected by magnetic fields?

A

It is an EM wave so has no charge so it isn’t deflected.

40
Q

Define half life.

A

Half life is the average time is takes for the number of nuclei in a radioactive isotope sample to halve.

41
Q

The activity of a radio isotope is 640 CPM (counts per minute) two hours later it has fallen to 80 CPM. What is the half life?

A

620/2=320 320/2=160 160/2=80.

This means three half lives over the course of two hours meaning one is 40 minutes.

42
Q

How and what can radiation be used for?

A

Smoke detectors, tracers in medicine, radiotherapy, sterilisation of food and surgical instruments.

43
Q

How can smoke detectors use radiation?

A

A weak source of alpha radiation is out close to two electrodes.
The source is ionising and causes an electrical flow between the two electrodes.
Smoke will absorb the radiation, breaking the circuit and sounding the alarm.

44
Q

How are radioactive tracers used in medicine?

A

Short life beta or game emitters are used. This is so the radiation can leave the body and so that exposure is kept to a minimum.
They are injected or swallowed by the body an an external detector tracks the progress.
Iodine 131 is is absorbed by the thyroid gland like normal iodine 127 but it gives out radiation which can be detected and doctors can determine whether the thyroid gland is working as it should.

45
Q

Explain how gamma rays are used in radiotherapy.

A

High does of gamma rays will kill all living cells so they can treat cancer.
However healthy cells will inevitably be damaged making the patient feel ill but it is worth it if the cancer is killed off.

46
Q

How can radiation be used to sterilise food or surgical instruments?

A

A high dose of gamma rays will kill all microbes, keeping food fresh for longer. The same can be done for medical instruments.
This is good as there are no high temperatures so food or plastic instruments aren’t damaged.
The isotope used needs to be a strong emitter of gamma radiation with a long half life so it doesn’t have to be replaced too often.

47
Q

How does radiation dame living cells?

A

Radiation will enter cells and collide with molecules.
This causes ionisation which damages or destroys them.
Lower doses cause minor damage with out killing the cell.
This can produce a mutant cell which will divide uncontrollably, causing cancer.
Higher does kill cells completely, causing radiation sickness.

48
Q

What can affect the harmful effects of radiation?

A

The exposure to the radiation.

The energy and penetration.

49
Q

Which types of radiation are most dangerous outside the body?

A

Beta and gamma a they can penetrate the skin and get to delicate organs. Alpha particles can’t do this.

50
Q

Which types of radiation are most dangerous inside the body?

A

Alpha radiation is. They don’t pass out and do all their damage in a very localised area.

51
Q

What safety precautions can be put in place to prevent the effects of radiation exposure?

A

When conducting an experiment, use the sources for the shortest possible time.
Don’t allow contact with skin. Only handle with tongs. Hold at arms length, minimising the radiation reaching the body.
Store radioactive sources in lead box and out them away when the experiment is over.
Wear a lead apron and stand behind a lead screen.

52
Q

What is nuclear fission?

A

It occurs in nuclear reactors. Uranium-235 and plutonium-239 and usually used.
A slow moving neutron is absorbed by a uranium or plutonium nucleus. This makes it unstable, causing it to split.
When a nucleus splits, two or three more neutrons will be produced. These may hit another nucleus, continuing the reaction.
When a large atom splits in two, two smaller nuclei will form. They are usually radioactive as they have the wrong number of neutrons.
A nucleus splitting produces energy.

53
Q

What are the disadvantages of nuclear power?

A

It produces waste that is highly radioactive. It is difficult and expensive to dispose of safely.
While fuel is cheap, the overall cost is high as the running and decommissioning of a plant is expensive.
It also carries the risk of radiation leaks from the plant or a catastrophe like Chernobyl.

54
Q

Explain nuclear fusion.

A

Two light nuclei (hydrogen) can join and this is called fusion.
It produces more energy than fission, doesn’t produce lots of radioactive radiation and is run on hydrogen which is plenty full.
However it can only happen at really high temperatures like 100000000 C.
It is hard to hold the hydrogen at such high pressure and temperature. An extremely strong magnetic field is used.
At the moment, all reactors take in more energy than the amount produced.

55
Q

How so stars start?

A

Initially they are clouds of dust and gas. The force of gravity makes the gas spiral together a forming a protostar.
Gravitational energy is converted to heat energy so the temperature rises. When it gets high enough, hydrogen nuclei undergo fusion to form helium nuclei producing lots of heat and light. The star has started.

56
Q

What is the main star sequence?

A

It is a long stable period where the outward force of the heat produced is equal to the inward pull of gravity. It uses it’s massive amounts of hydrogen to burn for billions of years.

57
Q

What happens when a star runs out of hydrogen?

A

The nuclear fission of helium occurs and heavier elements like iron are made. It swells and becomes a red giant or a red super giant. It becomes red and the surface cools.

58
Q

What happens to red giants?

A

It will become unstable, ejecting the outer layer of dust and gas as a planetary nebula. This leaves behind a hot dense solid core, a white dwarf which will cool to form a black dwarf.

59
Q

What happens to a red super giant?

A

They start to glow brightly again as they undergo more fusion and expand and contract serval times forming elements as heavy iron. Eventually they explode to form a supernova, forming all the other elements and ejecting them into space.

60
Q

What happens to an atom that has just produced an alpha particle?

A

The atomic number will decrease by two the the mass number by 4.

61
Q

What happens to an atom that has just produced a beta particle?

A

The atomic number will go up by one and the mass number stays the same.

62
Q

What happens to an atom that has just produced a gamma particle?

A

The atomic and mass number will stay the same.

63
Q

How can radiation be used to insure foil is of the correct thickness ?

A

A role of foil is put between two rollers. After the foil has gone through the rollers beta radiation is put through it and it is detected by a detector on the other side. It will be able to detect the thickness of the foil and adjust the rollers.

64
Q

How does carbon dating work?

A

When a living thing dies, it stops absorbing carbon. This will start to decay(half life of carbon is 5600 years)
They will compare the half life to the amount left and determine the age.

65
Q

What is the circuit symbol for a resistor?

A

An empty rectangle.

66
Q

What is the circuit symbol for a variable resistor?

A

An ordinary resistor ( an empty rectangle ) but with an arrow going right the way through it from south west to north east.

67
Q

What is the circuit symbol for an ammeter?

A

A circle with a capital A in it.

68
Q

What is the circuit symbol for a voltmeter?

A

A circle with a capital V in it.

69
Q

What is the circuit symbol for a thermistor?

A

The symbol for an ordinary resistor ( an empty rectangle) but in the bottom left corner, under the rectangle is a small horizontal line. This is attached to a diagonal line that goes through the rectangle and out the top left.

70
Q

What is the circuit symbol for a LDR?

A

A circle but with a small rectangle within it. This doesn’t touch any of the sides. It is connected to the outside wires. Two arrows going from the top left inwards are on the outside of the resistor are on the outside.

71
Q

Explain the axises of a potential difference current graph.

A

Current is on the Y axis and voltage on the X axis.

72
Q

Describe the potential difference current graph of a resistor.

A

Current and resistance are directly proportional.

It will be a strait line that goes through the centre. Different resistances will mean different gradients.

73
Q

Describe the potential difference current graph of a filament lamp.

A

It it curved. It goes through the centre and goes from the bottom left to top right. It starts off flat and end flat. In the centre it is at 45 degrees.

74
Q

Describe the potential difference current graph of a diode.

A

There will be a straight line going along the X axis which then curves up expediently after the Y axis.

75
Q

What is charge measured in?

A

Coulombs.

76
Q

What is work measured in ?

A

Joules.

77
Q

If you have a charged object and connect it to the ground, what will happen?

A

The additional electrons will flow into the ground.

78
Q

What happens to current in a series circuit?

A

It is always the same.

79
Q

When does current change?

A

It only changes when there are splits in the circuit.

80
Q

you have a parallel circuit with two paths, each with a resistor.
In one there is 0.5 amps and in the other 1.5 amps. How many more times is one resistor more powerful than the other?

A

1.5 divided by 0.5 = 3

Three times more resistance.

81
Q

You push a chair with constant speed with a force of 200 N for 5M. How much kinetic energy should it have?

A

Kinetic energy = work.
Work= force X distance.
200 X 5
=1000J

82
Q

In a parallel circuit, how is voltage the same?

A

The voltage lost in each path is always the same.

83
Q

What is the time period in a oscilloscope measured in?

A

Seconds.

84
Q

How is the time period found on a oscilloscope trace ?

A

The time base is the distance between the horizontal divisions. Count the number of divisions between two different peaks and times the two together. You should get something in seconds.

85
Q

What is the time base usually measured in?

A

In milliseconds. Each is 0.001s. They look like ms.

86
Q

What is left after a super nova?

A

The outer layer of dust and gas is gone leaving a very dense core called a neutron star. If the star was big enough, it will become a black hole.

87
Q

What is the frequency of UK electricity?

A

50 hertz.

88
Q

If you have a table showing the rate of radioactivity and the results differ a lot, what is a possible explanation?

A

Radioactive decay is a random process.

89
Q

What is the circuit symbol for a filament lamp?

A

A circle with a cross in it.

89
Q

What is the circuit symbol for a fuse?

A

A rectangle but with the line that represents the wire going through it.

89
Q

What is the circuit symbol for a LED.

A

A circle. There will be a triangle with in this pointing against a vertical line. Two arrows with come out from the LED in a north easterly direction.

GCSE Physics (6 decks)

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