How to calculate concentration

The acid we used was 20g/dm3. This means that there were 20g of HCl for every 1 dm3 (a dm3 is 1000cm3, which means it's 1 litre). This is a measure of concentration.

If we dilute the acid, we can work out the new concentration. To do this, we must first work out how strong it is compared to the original solution. Do this by dividing the volume of acid in the solution by the the total volume. For example, if you used 10cm3 of acid, mixed with 10cm3 of water, that gives a total volume of 20cm3. Volume of acid / Total volume = 10 / 20 = 0.5

This tells us that the solution is half as strong as the full strength acid (this makes sense - half of the volume of the solution was acid).

As another example, if we used 5cm3 of acid and 10cm3 of water, that means 5cm3 (acid) / 15cm3 (total volume) = 0.333 or 1/3



Once we've calculated the ratio, then we can multiply this by the original concentration. Our original concentration was 20g/dm3, so in our first example: 0.5 x 20g/dm3 gives us a new concentration of 10g/dm3.

ALTERNATIVELY: concentration is also displayed like this: 0.5M [the capital M stands for moles per dm3, where a mole is the name given to a specific number of atoms or molecules]. If you prefer, you can use this as a value of concentration. The full strength acid is 0.5M, so in our first example, the solution would have a concentration of 0.5 x 0.5 = 0.25M


If you put a column in your results table showing the concentration of the acid solution, that'll make your results look a lot more professional.

Climate Change

Global warming: http://www.youtube.com/watch?v=Z_jHP6xBLe8

The Greenhouse effect: http://www.youtube.com/watch?v=NFXR49hg8II

Sea levels: http://www.bbc.co.uk/learningzone/clips/evidence-for-global-warming-sea-level-change-no-narration/1496.html 

Is nuclear energy safe?

In P6 we learn about nuclear power in a lot of detail. The media may hype up some of the dangers related to nuclear energy but we need to be careful, as is clear from several disasters in recent history. Here's a link to a news section about the Fukushima plant, the site of a near disaster in Japan: http://www.theguardian.com/environment/fukushima

However it's not all one-sided: we can't ignore the benefits of nuclear energy - http://www.fi.edu/guide/wester/benefits.html 

Boosting your grade in the coursework

There are a number of things that you can include in the coursework to boost your grade.

Rate column in the table: the rate of a reaction is the speed at which a reaction takes place. So a faster reaction will take less time than a slow reaction. The rate of a reaction can be expressed by finding 1 / time. If you add a column to your table showing Rate as 1/ time, this will net you some bonus points, especially if you make a graph of this vs concentration.

Preliminary investigation: many experiments do a preliminary investigation to check and see what quantities are required before they perform the full experiment. For example, there's no point planning lots of different dilutions of acid if the time difference between each dilution was around 2 seconds... Before you do an experiment, if you're going to be very scientific, you need to check that you're using a suitable range of data. You could write in a section between your introduction and method that you did a preliminary test. In this preliminary test you used some rough dilutions to get an idea of how long it would take, and this would then allow you to decide the dilutions you would need for your final version.

There are some other examples of extra things we can put in, but they fit into the later sections, like the Conclusion and Evaluation, so we'll save them for later.

If you can't open the sample coursework:

Email me at the usual address, and I will send you a copy.

Calculating Averages for Coursework

As you know, an average is calculated by finding the sum of all the values, and then dividing this by the number of different values (so if there are 3 different results, divide the total by 3).

When we take a reading on a stopwatch, we have to be careful when calculating the average. First you have to convert the value to seconds, then add up. Here's an example:

If I took two readings, one was 3:42:07 (that's 3 minutes, 42.07 seconds) and one was 2:56:39, if we tried calculating the average in minutes, we would probably do (3.4207 + 2.5639) / 2. That would give an answer of 2.9923. 2 minutes and 99 seconds? That can't be right, and it's because there are 60 seconds in a minute, whereas decimals work in 100s.

Instead we need to convert the values to seconds. 3:42:07 becomes 222.07 seconds (because 3 minutes is 180 seconds, and 180 + 42 = 222). 2:56:39 becomes 176.39 seconds. The average is 199.23 seconds.

To be honest, it's probably neater and easier to keep your answer in seconds...

Any other questions about the Coursework?

If you have any other questions about the coursework, email them to the usual address (westfieldacademyscience dot gmail dot com)

What's in an Investigation?

I've taken some of the wording from the mark scheme and put it up here. The S stands for Strategy, and so these marks are given for your planning and background knowledge. 

S(a) – Write information about what affects a rate of reaction and pick one factor to test. What is your hypothesis, and prediction and why have you made this prediction.

This is your introduction. In it you can show off your knowledge about reactions, and even throw in a few diagrams to explain your points. Remember your hypothesis uses scientific knowledge to explain what you think will happen in your investigation from a theoretical perspective (think of particles and collisions), whereas your prediction is explaining the actual thing you will see (think of time taken for the beaker to change).

S(b) – Select and use appropriate techniques – how will you do the experiment. Justify the technique, and explain your range of data (including how many repeats). Complete full risk assessment, including how to minimise any harm.

This will be your method. Your range of data is the different solutions you will use (this depends on what variable you pick). Remember to explain the repeats you will use and why. A good risk assessment can come separately to the method, as a separate section. Don't just mention the risks but explain how you can avoid them and stay safe.

Coursework Reaction

The reaction in this video is very similar to the reaction we will be doing in our investigation: http://www.youtube.com/watch?v=r4IZDPpN-bk

This video shows a variation on the reaction, some of the terms will be unfamiliar (the capital M eg 0.5M, refers to concentration): http://www.youtube.com/watch?v=HWvf7HUshJY

Coursework Example

Here is an example of a write-up by a student that has done a similar investigation to the one we're doing this year. It is very detailed and there's a lot more in there than you would be expected to do, but it helps to see what a finished piece might look like. The biggest difference is that we are only changing one variable, whereas the student investigated several different variables.

If you can't open this link, email me and I will send you a copy (the address is westfieldacademyscience [at] gmail [dot] com )

http://www.thinkingwriting.qmul.ac.uk/wishees/collections/school/Morpeth%20GSCE%20Chemistry/PDFs/59367.pdf

Additional Coursework: Simulating Reactions

This simulation allows you to have a look at how changing different components in a reaction can have an effect on the rate. It's a little complicated, and more detailed than you'll need for your coursework, but playing with it will help you get comfortable with how to control a reaction: http://phet.colorado.edu/en/simulation/reactions-and-rates

The Rate Experiments tab is probably the best one for the coursework.

Electromagnetic Spectrum rap

This covers the 7 types of EM wave you need to remember for P2, and gives some of their uses. There's even a little bit about revision at the end: http://www.youtube.com/watch?v=A0un-_jBPPU

Additional Science Coursework: Rates of Reaction

This year's Additional coursework is investigating the factors that affect how quickly a reaction takes place. As part of the write-up you will need to explain why the rate of a reaction is affected by these factors. While this link from BBC Bitesize is based on a different exam board (AQA rather than OCR), it covers the basics of a reaction well: http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/reaction/ratesrev1.shtml 

P1 Specification

Module P1: The Earth and the Universe

P1.1 What do we know about the place of the Earth in the Universe?

1. recall that the Earth is one of eight planets moving in almost circular paths round the Sun

which, together with other smaller objects orbiting the Sun (asteroids, dwarf planets, comets)

and moons orbiting several planets, make up the solar system

2. describe the principal differences between planets, moons, the Sun, comets and asteroids

including their relative sizes and motions

3. understand that the solar system was formed over very long periods from clouds of gases and

dust in space, about five thousand million years ago

4. recall that the Sun is one of thousands of millions of stars in the Milky Way galaxy

5. recall that there are thousands of millions of galaxies, each containing thousands of millions of

stars, and that all of these galaxies make up the Universe

6. put in order and recall the relative sizes of: the diameters of the Earth, the Sun, the Earth’s

orbit, the solar system, the Milky Way, the distance from the Sun to the nearest star, and the

distance from the Milky Way to the nearest galaxy

7. understand that all the evidence we have about distant stars and galaxies comes from the

radiation astronomers can detect

8. recall that light travels through space (a vacuum) at a very high but  finite speed, 300 000 km/s

9. recall that a light-year is the distance travelled by light in a year

10. understand that the [1] nite speed of light means that very distant objects are observed as they

were in the past, when the light we now see left them

11. understand how the distance to a star can be measured using parallax (qualitative idea only)

12. understand how the distance to a star can be estimated from its relative brightness

13. understand that light pollution and other atmospheric conditions interfere with observations of

the night sky

14. explain why there are uncertainties about the distances of stars and galaxies with reference

to the nature and difficulty of the observations on which these are based and the assumptions

made in interpreting them

15. understand that the source of the Sun’s energy is the fusion of hydrogen nuclei

16. understand that all chemical elements with atoms heavier than helium were made in stars

17. understand that the redshift in the light coming from them suggests that distant galaxies

are moving away from us

18. understand that (in general) the further away a galaxy is, the faster it is moving away

from us

19. understand how the motions of galaxies suggests that space itself is expanding

20. recall and put in order the relative ages of the Earth, the Sun, and the Universe

21. recall that scientists believe the Universe began with a ‘big bang’ about 14 thousand million

years ago

22. understand that the ultimate fate of the Universe is dif[1] cult to predict because of difficulties in

measuring the very large distances involved and the mass of the Universe, and studying the

motion of very distant objects.

P1.2 What do we know about the Earth and how it is changing?

1. understand how rocks provide evidence for changes in the Earth (erosion and sedimentation,

fossils, folding)

2. understand that continents would be worn down to sea level by erosion, if mountains were not

being continuously formed

3. understand that the rock processes seen today can account for past changes

4. understand that the age of the Earth can be estimated from, and must be greater than, the

age of its oldest rocks, which are about four thousand million years old

5. understand Wegener’s theory of continental drift and his evidence for it (geometric [1] t of

continents and their matching fossils and rock layers)

6. understand how Wegener’s theory accounts for mountain building

7. understand reasons for the rejection of Wegener’s theory by geologists of his time (movement

of continents not detectable, too big an idea from limited evidence, simpler explanations of the

same evidence, Wegener an outsider to the community of geologists)

8. understand that sea floor spreading is a consequence of movement of the mantle (convection

due to heating by the core)

9. recall that sea floors spread by a few centimetres a year

10. understand how sea floor spreading and the periodic reversals of the Earth’s magnetic field can explain the pattern in the magnetisation of sea floor rocks on either side of the

oceanic ridges

11. understand that earthquakes, volcanoes and mountain building generally occur at the edges

of tectonic plates

12. understand how the movement of tectonic plates causes earthquakes, volcanoes and

mountain building, and contributes to the rock cycle

13. recall that earthquakes produce wave motions on the surface and inside the Earth which can

be detected by instruments located on the Earth’s surface

14. recall that earthquakes produce:

a. P-waves (longitudinal waves) which travel through solids and liquids

b. S-waves (transverse waves) which travel through solids but not liquids

15. describe the difference between a transverse and longitudinal wave

16. understand how differences in the wave speeds and behaviour of P-waves and S-waves can

be used to give evidence for the structure of the Earth

17. in relation to waves, use the equation:

distance = wave speed × time

(metres, m) (metres per second, m/s) (seconds, s)

18. draw and label a diagram of the Earth to show its crust, mantle and core

19. recall that a wave is a disturbance, caused by a vibrating source, that transfers energy in the

direction that the wave travels, without transferring matter

20. recall that the frequency of waves, in hertz (Hz), is the number of waves each second that are

made by the source, or that pass through any particular point

21. recall that the wavelength of waves is the distance between the corresponding points on two

adjacent cycles

22. recall that the amplitude of a wave is the distance from the maximum displacement to the

undisturbed position

23. draw and interpret diagrams showing the amplitude and the wavelength of waves

24. use the equation:

wave speed = frequency × wavelength

(metres per second, m/s) (hertz, Hz) (metres, m)

25. understand that for a constant wave speed the wavelength of the wave is inversely

proportional to the frequency.

© OCR 2011 GCSE Science A

P2 Specification

Module P2: Radiation and Life

P2.1 What types of electromagnetic radiation are there? What happens when radiation hits an object?

1. interpret situations in which one object affects another some distance away in terms of a

general model of electromagnetic radiation:

a. one object (a source) emits radiation

b. the radiation travels outwards from the source and can be reflected, transmitted or

absorbed (or a combination of these) by materials it encounters

c. radiation may affect another object (a detector) some distance away, when it is absorbed

2. understand that light is one of a family of radiations called the electromagnetic spectrum

3. understand that a beam of electromagnetic radiation transfers energy in ‘packets’ called

photons

4. understand that the higher the frequency of an electromagnetic radiation, the more energy is

transferred by each photon

5. list the electromagnetic radiations in order of the energy transferred by each photon, or in

order of frequency:

radio waves, microwaves, infrared, red visible light violet, ultraviolet, X-rays, gamma rays

6. recall that all types of electromagnetic radiation travel at exactly the same, very high but finite,

speed through space (a vacuum) of 300 000 km/s

7. understand that the energy arriving at a square metre of surface each second is a useful

measure of the strength (or ‘intensity’) of a beam of electromagnetic radiation

8. understand that the energy transferred to an absorber by a beam of electromagnetic radiation

depends on both the number of photons arriving and the energy of each photon

9. understand that the intensity of a beam of electromagnetic radiation decreases with distance

from the source and explain why, in terms of the ever increasing surface area it reaches

and its partial absorption by the medium it travels through

10. understand that some electromagnetic radiations (ultraviolet radiation, X-rays, gamma rays)

have enough energy to change atoms or molecules, which can initiate chemical reactions

11. recall that high energy ultraviolet radiation, X-rays and gamma rays can cause ionisation

12. understand that the electromagnetic radiations which are ionising are those with high enough

photon energy to remove an electron from an atom or molecule (ionisation).

P2.2 Which types of electromagnetic radiation harm living tissue and why?

1. understand that the heating effect of absorbed radiation can damage living cells

2. relate the heating effect when radiation is absorbed to its intensity and duration

3. understand that some people have concerns about health risks from low intensity microwave

radiation, for example from mobile phone handsets and masts, though the evidence for this is

disputed

4. understand that some microwaves are strongly absorbed by water molecules and so can be

used to heat objects containing water

5. understand that the metal cases and door screens of microwave ovens reflect or absorb

microwave radiation and so protect users from the radiation

6. recall that some materials (radioactive materials) emit ionising gamma radiation all the time

7. understand that with increased exposure to ionising radiation, damage to living cells increases

eventually leading to cancer or cell death

8. understand that the ozone layer absorbs ultraviolet radiation, emitted by the Sun, producing

chemical changes in that part of the atmosphere

9. understand that the ozone layer protects living organisms from some of the harmful effects of

ultraviolet radiation

10. recall that sun-screens and clothing can be used to absorb some of the ultraviolet radiation

from the Sun

11. recall that physical barriers absorb some ionising radiation, for example: X-rays are absorbed

by dense materials so can be used to produce shadow pictures of bones in our bodies or of

objects in aircraft passengers’ luggage, and radiographers are protected from radiation by

dense materials such as lead and concrete.

P2.3 What is the evidence for global warming, why might it be occurring, and how serious a threat is it?

1. understand that all objects emit electromagnetic radiation with a principal frequency that

increases with temperature

2. recall that the Earth is surrounded by an atmosphere which allows some of the

electromagnetic radiation emitted by the Sun to pass through

3. recall that this radiation warms the Earth’s surface when it is absorbed

4. understand that the radiation emitted by the Earth, which has a lower principal frequency

than that emitted by the Sun, is absorbed or reflected back by some gases in the

atmosphere; this keeps the Earth warmer than it would otherwise be and is called the

greenhouse effect

5. recall that one of the main greenhouse gases in the Earth’s atmosphere is carbon dioxide,

which is present in very small amounts

6. recall that other greenhouse gases include methane, present in very small amounts, and

water vapour

7. interpret simple diagrams representing the carbon cycle

8. use the carbon cycle to explain:

a. why, for thousands of years, the amount of carbon dioxide in the Earth’s atmosphere

was approximately constant

b. that some organisms remove carbon dioxide from the atmosphere by photosynthesis

(eg green plants) and many organisms return carbon dioxide to the atmosphere by

respiration as part of the recycling of carbon

c. why, during the past two hundred years, the amount of carbon dioxide in the atmosphere

has been steadily rising

9. recall that the rise in atmospheric carbon dioxide is largely the result of:

a. burning increased amounts of fossil fuels as an energy source

b. cutting down or burning forests to clear land

10. understand that computer climate models provide evidence that human activities are

causing global warming

11. understand how global warming could result in:

a. it being impossible to continue growing some food crops in particular regions because of

climate change

b. more extreme weather events, due to increased convection and larger amounts of

water vapour in the hotter atmosphere

c. flooding of low lying land due to rising sea levels, caused by melting continental ice and

expansion of water in the oceans.

P2.4 How are electromagnetic waves used in communications?

1. understand that electromagnetic radiation of some frequencies can be used for transmitting

information, since:

a. some radio waves and microwaves are not strongly absorbed by the atmosphere so can

be used to carry information for radio and TV programmes

b. light and infrared radiation can be used to carry information along optical fibres because

the radiation travels large distances through glass without being significantly absorbed

2. recall that information can be superimposed on to an electromagnetic carrier wave, to create a

signal

3. recall that a signal which can vary continuously is called an analogue signal

4. recall that a signal that can take only a small number of discrete values (usually two) is called

a digital signal

5. recall that sound and images can be transmitted digitally (as a digital signal)

6. recall that, in digital transmission, the digital code is made up from just two symbols, ‘0’ and ‘1’

7. understand that this coded information can be carried by switching the electromagnetic carrier

wave off and on to create short bursts of waves (pulses) where ‘0’ = no pulse and ‘1’ = pulse

8. recall that when the waves are received, the pulses are decoded to produce a copy of the

original sound wave or image

9. understand that an important advantage of digital signals over analogue signals is that if the

original signal has been affected by noise it can be recovered more easily and explain why

10. recall that the amount of information needed to store an image or sound is measured in bytes

(B)

11. understand that, generally, the more information stored the higher the quality of the sound or

image

12. understand that an advantage of using digital signals is that the information can be stored and

processed by computers.

© OCR 2011 GCSE Science A

P3 Specification

Module P3: Sustainable Energy

P3.1 How much energy do we use?

1. understand that the demand for energy is continually increasing and that this raises issues

about the availability of energy sources and the environmental effects of using these sources

2. recall the main primary energy sources that humans use: fossil fuels (oil, gas, coal), nuclear

fuels, biofuels, wind, waves, and radiation from the Sun

3. understand why electricity is called a secondary energy source

4. understand that power stations which burn fossil fuels produce carbon dioxide which

contributes to global warming and climate change

5. understand that when electric current passes through a component (or device), energy is

transferred from the power supply to the component and/or to the environment

6. recall that the power (in watts, W) of an appliance or device is a measure of the amount of

energy it transfers each second, ie the rate at which it transfers energy

7. use the following equation to calculate the amount of energy transferred in a process, in joules

and in kilowatt hours:

energy transferred = power × time

(joules, J)            (watts, W)           (seconds, s)

OR

(kilowatt hours, kWh) (kilowatts, kW) (hours, h)

8. use the following equation to calculate the rate at which an electrical device transfers energy:

power = voltage × current

(watts, W) (volts, V) (amperes, A)

9. understand that a joule is a very small amount of energy, so a domestic electricity meter

measures the energy transfer in kilowatt hours

10. calculate the cost of energy supplied by electricity given the power, the time and the cost per

kilowatt hour

11. interpret and process data on energy use, presented in a variety of ways

12. interpret and construct Sankey diagrams to show understanding that energy is conserved

13. use the following equation in the context of electrical appliances and power stations:

efficiency =  energy usually transferred                 × 100%

total energy supplied

Candidates will be expected to consider / calculate efficiency as a decimal ratio and as a

percentage

14. suggest examples of ways to reduce energy usage in personal and national contexts.

P3.2 How can electricity be generated?

1. understand that electricity is convenient because it is easily transmitted over distances and can

be used in many ways

2. recall that mains electricity is produced by generators

3. understand that generators produce a voltage across a coil of wire by spinning a magnet near

it

4. understand that the bigger the current supplied by a generator, the more primary fuel it uses

every second

5. understand that in many power stations a primary energy source is used to heat water; the

steam produced drives a turbine which is coupled to an electrical generator

6. label a block diagram showing the basic components and structures of hydroelectric, nuclear

and other thermal power stations

7. understand that nuclear power stations produce radioactive waste

8. understand that radioactive waste emits ionising radiation

9. understand that with increased exposure to ionising radiation, damage to living cells increases

eventually leading to cancer or cell death

10. understand the distinction between contamination and irradiation by a radioactive material, and

explain why contamination by a radioactive material is more dangerous than a short period of

irradiation from the radioactive material

11. understand that many renewable sources of energy drive the turbine directly eg hydroelectric,

wave and wind

12. interpret a Sankey diagram for electricity generation and distribution that includes information

on the efficiency of energy transfers

13. recall that the mains supply voltage to our homes is 230 volts

14. understand that electricity is distributed through the National Grid at high voltages to reduce

energy losses.

P3.3 Which energy sources should we choose?

1. discuss both qualitatively and quantitatively (based on given data where appropriate), the

effectiveness of different choices in reducing energy demands in:

a. domestic contexts

b. work place contexts

c. national contexts

2. understand that the choice of energy source for a given situation depends upon a number of

factors including:

a. environmental impact

b. economics

c. waste produced

d. carbon dioxide emissions

3. describe advantages and disadvantages of different energy sources, including

non-renewable energy sources such as:

a. fossil fuels

b. nuclear

and renewable energy sources such as:

c. biofuel

d. solar

e. wind

f. water (waves, tides, hydroelectricity)

g. geothermal

4. interpret and evaluate information about different energy sources for generating electricity,

considering:

a. efficiency

b. economic costs

c. environmental impact

d. power output and lifetime.

5. understand that to ensure a security of electricity supply nationally, we need a mix of

energy sources.

© OCR 2011 GCSE Science A

P6 Specification

Module P6: Radioactive Materials

P6.1 Why are some materials radioactive?

1. recall that some elements emit ionising radiation all the time and are called radioactive

2. understand that radioactive elements are naturally found in the environment, contributing to

background radiation

3. understand that an atom has a nucleus, made of protons and neutrons, which is surrounded

by electrons

4. understand that the results of the Rutherford-Geiger-Marsden alpha particle scattering

experiment provided evidence that a gold atom contains a small, massive, positive region

(the nucleus)

5. understand that protons and neutrons are held together in the nucleus by a strong

force which balances the repulsive electrostatic force between the protons

6. understand that, if brought close enough together, hydrogen nuclei can fuse into helium

nuclei releasing energy, and that this is called nuclear fusion

7. understand that Einstein’s equation E = mc2 is used to calculate the energy released

during nuclear fusion and fission (where E is the energy produced, m is the mass lost

and c is the speed of light in a vacuum)

energy =              mass      ×             [speed]2

(joules, J) (kilograms, kg) ([metres per second]2, [m/s]2)

8. understand that every atom of any element has the same number of protons but the

number of neutrons may differ, and that forms of the same element with different

numbers of neutrons are called isotopes

9. understand that the behaviour of radioactive materials cannot be changed by chemical or

physical processes

10. recall that three types of ionising radiation (alpha, beta and gamma) are emitted by

radioactive materials and that alpha particles consist of two protons and two neutrons,

and that beta particles are identical to electrons

11. recall the penetration properties of each type of radiation

12. describe radioactive materials in terms of the instability of the nucleus, radiation

emitted and the element left behind

13. complete nuclear equations for alpha and beta decay

14. understand that, over time, the activity of radioactive sources decreases

15. understand the meaning of the term half-life

16. understand that radioactive elements have a wide range of half-life values

17. carry out simple calculations involving half-life.

P6.2 How can radioactive materials be used and handled safely, including wastes?

1. understand that ionising radiation can damage living cells and these may be killed or may

become cancerous

2. understand that ionising radiation is able to break molecules into bits (called ions), which

can then take part in other chemical reactions

3. recall and explain how ionising radiation can be used:

a. to treat cancer

b. to sterilise surgical instruments

c. to sterilise food

d. as a tracer in the body

4. recall that radiation dose (in sieverts) (based on both amount and type of radiation) is a

measure of the possible harm done to your body

5. interpret given data on risk related to radiation dose

6. understand that radioactive materials expose people to risk by irradiation and contamination

7. understand that we are irradiated and contaminated by radioactive materials all the time and

recall the main sources of this background radiation

8. relate ideas about half-life and background radiation to the time taken for a radioactive

source to become safe

9. recall categories of people who are regularly exposed to risk of radiation and that their

exposure is carefully monitored, including radiographers and workers in nuclear power

stations

10. understand that a nuclear fuel is one in which energy is released by changes in the nucleus

11. know that in nuclear fission, a neutron splits a large and unstable nucleus (limited to

uranium and plutonium) into two smaller parts, roughly equal in size, releasing more

neutrons

12. recall that the amount of energy released during nuclear fission is much greater than that

released in a chemical reaction involving a similar mass of material

13. understand how the nuclear fission process in nuclear power stations is controlled,

and use the terms chain reaction, fuel rod, control rod and coolant

14. understand that nuclear power stations produce radioactive waste

15. understand that nuclear wastes are categorised as high level, intermediate level and low

level, and relate this to disposal methods.

© OCR 2011 GCSE Science A

P5 Specification

Module P5: Electrical Circuits

P5.1 Electric current – a flow of what?

1. explain that when two objects are rubbed together they become charged, because electrons

are transferred from one object to the other

2. recall that objects with similar charges repel, and objects with opposite charges attract

3. explain simple electrostatic effects in terms of attraction and repulsion of charges

4. recall that electrons are negatively charged

5. recall that electric current is a flow of charge

6. recall that electric current is measured in amperes

7. understand that in an electric circuit the metal conductors (the components and wires)

contain many charges that are free to move

8. understand that when a circuit is made, the battery causes these free charges to move, and

that they are not used up but flow in a continuous loop

9. recall that in metallic conductors an electric current is a movement of free electrons that are

present throughout such materials

10. understand that in metal conductors there are lots of charges free to move but in an insulator

there are few charges free to move.

11. describe how an ammeter should be connected in a circuit to measure the flow of current at

a chosen point.

P5.2 What determines the size of the current in an electric circuit and the energy it

transfers?

1. recall that the larger the voltage of the battery in a given circuit, the bigger the current

2. recall that components (for example, resistors, lamps, motors) resist the flow of charge

through them

3. recall that the larger the resistance in a given circuit, the smaller the current will be

4. recall that the resistance of connecting wires is so small that it can usually be ignored

5. understand that when electric charge flows through a component (or device), work is

done by the power supply, and energy is transferred from it to the component and/or its

surroundings

6. recall that power (in watts, W) is a measure of the rate at which an electrical power supply

transfers energy to an appliance or device and/or its surroundings

7. use the equation:

power = voltage × current

(watts, W) (volts, V) (amperes, A)

8. recall that resistors get hotter when there is an electric current through them, and

understand that this heating effect is caused by collisions between the moving

charges and stationary ions in the wire

9. recall that this heating effect makes a lamp filament hot enough to glow

10. describe how the resistance of an LDR varies with light intensity

11. describe how the resistance of a thermistor (ntc only) varies with temperature

12. recognise and use the electrical symbols for a cell, power supply, filament lamp, switch,

LDR, fixed and variable resistor, thermistor, ammeter and voltmeter

13. understand that two (or more) resistors in series have more resistance than either one on its

own, because the battery has to move charges through both of them

14. understand that two (or more) resistors in parallel provide more paths for charges to move

along than either resistor on its own, so the total resistance is less

15. use the equation:

resistance (ohms, Ω)                      =             voltage (volts, V)

                                                                         ––––––––––––––

             current (amperes, A)

16. describe in words, or using a sketch graph, how the current through a component varies with

voltage across it when the resistance stays constant.

P5.3 How do parallel and series circuits work?

1. describe how a voltmeter should be connected to measure the potential difference between

any two chosen points

2. recall that the voltage across a battery (measured in V) provides a measure of the ‘push’ of

the battery on the charges in the circuit

3. recall that potential difference is another term for voltage

4. relate the potential difference between two points in the circuit to the work done on, or by, a

given amount of charge as it moves between these points

5. describe the effect on potential difference and current of adding further identical batteries in

series and in parallel with an original single one

6. understand that when two (or more) components are connected in series to a battery:

a. the current through each component is the same

b. the potential differences across the components add up to the potential difference

across the battery (because the work done on each unit of charge by the battery

must equal the work done by it on the circuit components)

c. the potential difference is largest across the component with the greatest resistance,

because more work is done by the charge moving through a large resistance

than through a small one

d. a change in the resistance of one component (variable resistor, LDR or

thermistor) will result in a change in the potential differences across all the

components

7. understand that when several components are connected in parallel directly to a battery:

a. the potential difference across each component is equal to the potential

difference of the battery

b. the current through each component is the same as if it were the only

component present

c. the total current from (and back to) the battery is the sum of the currents through

each of the parallel components

d. the current is largest through the component with the smallest resistance, because

the same battery voltage causes a larger current to flow through a smaller

resistance than through a bigger one.

P5.4 How is mains electricity produced? How are voltages and currents induced?

1. recall that mains electricity is produced by generators

2. recall that generators produce a voltage by a process called electromagnetic induction

3. understand that when a magnet is moving into a coil of wire a voltage is induced across the

ends of the coil

4. understand that if the magnet is moving out of the coil, or the other pole of the magnet is

moving into it, there is a voltage induced in the opposite direction

5. understand that if the ends of the coil are connected to make a closed circuit, a current will

flow round the circuit

6. understand that a changing magnetic field caused by changes in the current in one coil of

wire can induce a voltage in a neighbouring coil

7. describe the construction of a transformer as two coils of wire wound on an iron core

8. understand that a changing current in one coil of a transformer will cause a changing

magnetic field in the iron core, which in turn will induce a changing potential

difference across the other transformer coil

9. recall that a transformer can change the size of an alternating voltage

10. use the equation:

voltage across primary coil                                           number of turns in primary coil

––––––––––––––––––––––––––                             ––––––––––––––––––––––––––

voltage across secondary coil                      =             number of turns in secondary coil

11. describe how, in a generator, a magnet or electromagnet is rotated within a coil of wire to

induce a voltage across the ends of the coil

12. understand that the size of this induced voltage can be increased by:

a. increasing the speed of rotation of the magnet or electromagnet

b. increasing the strength of its magnetic field

c. increasing the number of turns on the coil

d. placing an iron core inside the coil

13. describe how the induced voltage across the coil of an a.c. generator (and hence

the current in an external circuit) changes during each revolution of the magnet or

electromagnet

14. understand that when the current is always in the same direction, it is a direct current (d.c.),

e.g. the current from a battery

15. recall that mains electricity is an a.c. supply

16. understand that a.c. is used because it is easier to generate than d.c., and is easier

and simpler to distribute over long distances

17. recall that the mains domestic supply in the UK is 230 volts.

P5.5 How do electric motors work?

1. understand that a current-carrying wire or coil can exert a force on a permanent magnet, or

on another current-carrying wire or coil nearby

2. understand that a current-carrying wire, if placed in a magnetic field whose lines of force are

at right-angles to the wire, experiences a force at right angles to both the current direction

and the lines of force of the field

3. recall that a current-carrying wire that is parallel to the lines of force of a magnetic field

experiences no force

4. explain how the motor effect can result in a turning force on a rectangular current-carrying

coil placed in a uniform magnetic field

5. understand that the motor effect can be used to produce continuous rotation of the coil, by

using a commutator to ensure that the direction of the current in the coil is reversed at an

appropriate point in each revolution

6. explain the role and use of motors in devices including domestic appliances, hard disc

drives, DVD players and electric motor vehicles.

© OCR 2011 GCSE Science A