PhysicsRevision

P1

Physics Unit P1 Topic 1 Visible light and the Solar System

1.1 Be able to describe how ideas about the structure of the Solar System have changed over time, including the change from the geocentric to the heliocentric models and the discovery of new planets.

o The geocentric model: The sun, moon, planets, and stars ie everything, all orbited the Earth in a series of concentric circles.

This model originates from ancient Greek civilisation 2000-2500 years ago and lasted for 1500-2000 years.

o The heliocentric model: The Earth and other planets orbited our sun -then considered as the centre of our universe.

Astronomers such as Copernicus working in the mid-16th century, were making observations and calculations to explain the movement of the planets without the geocentric model and that a heliocentric model fitted the data better.

Copernicus published his heliocentric theory and calculations in 1543, just in time, two months before his death!

The Catholic Church was not too impressed by the scientific model challenging the religious view of how our 'universe' works.

o Our contemporary model: The 8 major planets, minor planets and asteroids orbit the Sun in slightly elliptical orbits (our 'Solar System'), but our Sun is just one of millions-billions of stars in our galaxy (we see part of it as the 'Milky Way') and in turn the observable universe itself contains billions of other galaxies.

1.2 Be able to show an understanding of how scientists use waves to find out information about our Universe, including:

o a) the Solar System - the Sun and orbiting planets and asteroids The movement of the planets and asteroids has been observed from visible

light (reflected sunlight) for thousands of years, initially with the naked eye and from the early 16th century onwards, with telescopes.

With modern techniques, the Sun can be observed by detecting emissions in various regions of the electromagnetic spectrum eg infrared, visible light, ultraviolet, X-rays and even gamma ray emissions.

o b) the Milky Way - the view looking through our own galaxy Until relatively recently, the Milky Way galaxy, has been observed with the

naked eye and then telescopes on Earth, but now it can be viewed through powerful telescopes on satellites eg the Hubble Space Telescope. Our galaxy, and for that matter distant galaxies, can be continually observed using everything from giant radio telescopes, huge optical\visible light telescopes to gamma ray burst detectors.

1.3 Be able to discuss how Galileo’s observations of Jupiter, using the telescope, provided evidence for the heliocentric model of the Solar System.

o Galileo, in the early 17th century, working with the newly invented telescope, found his view of the 'universe' in conflict with that of the Catholic Church, especially after discovering moons orbiting around the planet Jupiter, which meant not everything orbited the Earth and the geocentric model was flawed.

1.4 Be able to compare methods of observing the Universe using visible light, including the naked eye, photography and telescopes.

o In observing the night sky, the naked eye, apart from aesthetic appreciation, has been largely replaced by photography, usually coupled to a telescope.

o However, historically, stars, planes, comets, our Moon have all been successfully discovered, observed, mapped and plotted via naked eye observations and astronomical tables of data assembled.

o Distant stars can be seen because they are so hot and powerful emitters of electromagnetic radiation eg visible light.

o Telescopes off much better light gathering power than the naked eye and the lens and lens-reflecting mirror systems can produced greatly magnified images and can peer into deep space totally inaccessible to the naked eye.

o Photographing the same patch of sky and comparing images from one night to another can show up whether an object is moving eg asteroid or comet or some new star appearing or an old star exploding in a massive supernovae explosion,.

o So, anything that changing that reflects or emits visible light can be detected and by using long-time exposures you can detect very faint very distant objects.

o The result of all these historical and continuing contemporary observations with telescopes of all kinds is to give us a pretty good picture of the observable universe, even if we don't fully understand how it all works!

1.5 Be able to explain how to measure the focal length of a converging lens using a distant object (see Ray diagram 2 below).

1.6 You should revise any investigations on the behaviour of converging lenses, including real and virtual images.

oo Ray diagram 1 (above): o

o Ray diagram 2 (above):

o

o Ray diagram 3 (above): o

o Ray diagram 4 (above): o

o Ray diagram 5 (above): 1.7 Revise any investigations on the use of converging lenses to:

o a) measure the focal length using a distant object o b) investigate factors which affect the magnification of a converging lens (formulae

are not needed) See section 1.7 for further notes and ray diagrams.

1.8 Be able to explain how the eyepiece of a simple telescope magnifies the image of a distant object produced by the objective lens (ray diagrams are not necessary).

1.9 Be able to describe how a reflecting telescope works. 1.10 Know that waves are reflected and refracted at boundaries between different materials.

oo Refraction diagram above.

the vertical .... lines are the two normal angles 1 and 3 = angles of incidence angles 2 and 4 = angles of refraction note that when a ray enters a more dense medium (air ==> glass), the ray

bends towards the normal, and on entering a less dense medium (glass ==> air) the ray bends away from the normal

there maybe a little reflection of incident rays 1 and 3, but most of the rays are refracted.

1.11 HT only: Be able to explain how waves will be refracted at a boundary in terms of the change of speed and direction.

o

o The above diagram illustrates the phenomena of refraction by considering what happens to waves eg visible light.

o You can think of the parallel lines as representing a series of crests of waves eg think waves on the sea or ripples in a pond on throwing a stone in.

o Refraction A: When waves from a less dense medium, hit a boundary interface, and enter a more dense medium, the waves 'bend towards the normal' ie refraction occurs.

This happens because on entering the more dense medium, the waves slow down causing the change wave in direction.

The obvious examples you see in optics experiments are light rays passing from air into more dense transparent plastic blocks or triangular and rectangular glass prisms.

o Refraction B: When waves from a more dense medium, hit a boundary interface, and enter a less dense medium, the waves 'bend away from the normal' ie refraction occurs.

This happens because on entering the less dense medium, the waves speed up causing the change in wave direction.

The obvious examples you see in optics experiments are light rays emerging from transparent plastic blocks or triangular and rectangular glass prisms, and passing out into less dense air.

When you observe an object half in water and half in air e.g. poking a stick into still water, you see a 'bent' distorted image, because, the light rays from the object and bent at the air-water interface because of refraction.

o If the waves hit the interface at an angle of 90o (perpendicular) to the interface between the two mediums, there is still a change in speed and wavelength, but there is NO refraction and the wave frequency remains the same.

1.12 Be able to describe that waves transfer energy and information without transferring matter.

o When your TV receives the signal its just coded data in the electromagnetic wave, no material substance arrives!

o However, energy itself must be transmitted or no effected could be produced by the TV receiver!

o Similarly, when ripples on water cause floating objects to bob up and down, energy is needed to do this, but neither the floating object or the water itself actually move in the direction of the transverse waves.

o The most dramatic transfer of energy involves earthquake waves, both transverse and longitudinal, yet the effects are transmitted and felt miles from the epicentre and no part of the earth's crust moves in the direction of the seismic waves but it may move violently from side to side, up and down or compressed/decompressed.

o When sound waves vibrate your ear drum no air moves from the TV, person or musical instrument etc., yet energy is transferred through the medium of air, otherwise, what causes your ear drum to vibrate!

The above diagram gives an idea of a transverse wave where the oscillations are at 90o to the direction the wave moves

eg electromagnetic radiation, ripples-waves on water, shaking slinky spring from side to side

The above diagram gives an idea of a longitudinal wave where the oscillations are in the direction the wave moves

eg sound waves, push and pulling on a slinky spring

1.13 Understand and be able to use the terms of frequency, wavelength, amplitude and speed to describe waves (see diagrams above).

o The top of the wave form is called a crest and the bottom of the wave is called the trough.

o The wave amplitude = distance from the baseline of zero displacement to the point of maximum displacement (to top of crest or to bottom of trough)

o One wavelength (m) = distance of one complete cycle or oscillation = horizontal distance from any point on the wave until where it begins to repeat = distance between two crests = distance between two troughs

o The frequency of a wave (Hz) = number of complete cycles/oscillations per second = number of complete waves passing a given point per second. 1 Hertz, x Hz = x oscillation/s

1.14 Know the differences between longitudinal and transverse waves by referring to sound, electromagnetic and seismic waves.

o You need to understand that in a transverse wave the oscillations are perpendicular (at 90o) to the direction of energy transfer, but in a longitudinal wave the oscillations are parallel to the direction of energy transfer ie direction of forward wave movement.

o Shaking a slinky spring from side to side produces a transverse wave, as ripples on water and all electromagnetic radiation.

o Pulling and pushing on a slinky spring produces pulses of energy transmitted as a longitudinal wave like a sound wave travelling through a medium ie the 'compressions' and 'rarefactions' are in the same direction as the wave movement.

o Electromagnetic waves - o Sound waves - o Seismic waves - can be of both types of wave.

1.15 Be able to use both the equations below for all waves (HT only: and their rearrangements):

o appropriate units used in ()

o a) wave speed (metre/second, m/s) = frequency (hertz, Hz) x wavelength (metre, m)

in 'shorthand' v = f x λ rearrangements: f = v / λ and λ = v / f

o b) wave speed (metre/second, m/s) = distance (metre, m) / time (second, s) in 'shorthand' v = d / t

rearrangements: d = v x t and t = d / v This is the general formula for the speed or velocity of anything moving.

o (a) , (b)

Physics Unit P1 Topic 2 The electromagnetic spectrum

2.1 You must be able to show an understanding of how Herschel and Ritter contributed to the discovery of waves outside the limits of the visible spectrum.

2.2 Be able to understand that all electromagnetic waves are transverse and that they travel at the same speed in a vacuum.

2.3 Be able to describe the continuous electromagnetic spectrum including (in order) o radio waves, microwaves, infrared, visible(*), ultraviolet, X-rays and gamma

rays o ==> increasing frequency, decreasing wavelength, increasing energy o (* including the colours of the visible spectrum - red, orange, yellow, green, blue,

indigo, violet) 2.4 Be able to understand that the electromagnetic spectrum is continuous from radio waves

to gamma rays, but the radiations within it can be grouped in order of decreasing wavelength and increasing frequency.

Electromagnetic radiation Radio waves Microwaves Infrared radiation Visible light Ultraviolet

light X-rays Gamma rays

Energy ========= increasing energy of radiation ======>Frequency === increasing frequency of radiation (Hz) ======>

Wavelength ====== decreasing wavelength of radiation (m) ======>

'picture trend'===============>

2.5 Be able to understand that the potential danger associated with an electromagnetic wave increases with increasing frequency.

2.6 Be able to relate the harmful effects, to life, of excessive exposure to the frequency of the electromagnetic radiation, including:

o a) microwaves: internal heating of body cells o b) infrared: skin burns

o c) ultraviolet: damage to surface cells and eyes, leading to skin cancer and eye conditions

o d) X-rays and gamma rays: mutation or damage to cells in the body 2.7 Be able to describe some uses of electromagnetic radiation:

o a) radio waves: including broadcasting, communications and satellite transmissions o b) microwaves: including cooking, communications and satellite transmissions o c) infrared: including cooking, thermal imaging, short range communications, optical

fibres, television remote controls and security systems o d) visible light: including vision, photography and illumination o e) ultraviolet: including security marking, fluorescent lamps, detecting forged bank

notes and disinfecting water o f) X-rays: including observing the internal structure of objects, airport security

scanners and medical X-rays o g) gamma rays: including sterilising food and medical equipment, and the detection of

cancer and its treatment 2.8 Know that ionising radiations are emitted all the time by radioactive sources 2.9 You should know that ionising radiation includes alpha and beta particles and gamma

rays and that they transfer energy.

Physics Unit P1 Topic 3 Waves and the Universe

3.1 Know that the Solar System is part of the Milky Way galaxy. 3.2 Know a galaxy as a collection of stars. 3.3 Know that the Universe includes all of the galaxies. 3.4 Be able to compare the relative sizes of and the distances between the Earth, the Moon,

the planets, the Sun, galaxies and the Universe. 3.5 Be able to describe the use of other regions of the electromagnetic spectrum by some

modern telescopes. 3.6 Be able to describe the methods used to gather evidence for life beyond Earth, including

space probes, soil experiments by lunar/planetary landers, Search for Extraterrestrial Intelligence (SETI)

3.7 Be able to demonstrate an understanding of the impact of data gathered by modern telescopes on our understanding of the Universe, including:

o a) the observation of galaxies because of improved magnification o b) the discovery of objects not detectable using visible light o c) the ability to collect more data

3.8 Appreciate the basic design of a simple spectrometer and it is used to analyse common (visible) light sources.

3.9 Be able to explain why some telescopes are located outside the Earth’s atmosphere 3.10 HT only: Be able to analyse data provided to support the location of telescopes outside

the Earth’s atmosphere 3.11 Be able to describe the evolution of stars of similar mass to the Sun through the

following stages: o a) nebula o b) star (main sequence) o c) red giant d white dwarf

3.12 Be able to describe the role of gravity in the life cycle of stars 3.13 HT only: Be able to describe how the evolution of stars with a mass larger than the Sun

is different, and may end in a black hole or neutron star 3.14 Be able to describe and understanding of the basic ideas in the Steady State and Big

Bang theories of the cosmos-universe.. 3.15 Be able to describe evidence supporting the Big Bang theory, limited to red-shift and the

cosmic microwave background (CMBR) radiation

3.16 Be able to recognise that as there is more evidence supporting the Big Bang theory than the Steady State theory, and the Big Bang theory is the currently accepted model for the origin of the Universe.

3.17 Be able to describe that if a wave source is moving relative to an observer there will be a change in the observed frequency and wavelength (called the 'Doppler Shift')..

3.18 HT only: Be able to demonstrate an understanding that if a wave source is moving relative to an observer there will be a change in the observed frequency and wavelength.

3.19 HT only: Be able to describe the red-shift in light received from galaxies at different distances away from the Earth.

3.20 HT only: Be able to explain why the red-shift of galaxies provides evidence for the Universe expanding.

3.21 HT only: Be able to explain how both the Big Bang and Steady State theories of the origin of the Universe both account for red-shift of galaxies.

3.22 HT only: Be able to explain how the discovery of the CMB radiation led to the Big Bang theory becoming the currently accepted model.

Extra notes for 3.14 to 3.22 a) Know and understand that if a wave source is moving relative to an observer there will be a

change in the observed wavelength and frequency.o Know that this is called the Doppler effect.

For the Doppler effect you should know that: The wave source could be light, sound or microwaves. When the source moves away from the observer, the observed

wavelength increases and the frequency decreases because the waves get stretched out.

When the source moves towards the observer, the observed wavelength decreases and the frequency increases because the waves become compressed.

You experience the Doppler effect quite clearly when a loud racing car or train passes by you.

As the loud moving object approaches you, the frequency (pitch) of the sound waves increases as oncoming sound waves are compressed (increasingly shorter wavelength).

As the object moves away from you, the frequency (pitch) decreases as the waves stretch out (wavelength becoming increasingly longer).

This is an effect, quite distinct from the fact that the sound of the moving object becomes louder then softer as the object passes you.

The Doppler effect on light waves is used to measure the speed at which the galaxies seem to be moving away from us-our galaxy in all directions!

This 'astronomical' Doppler effect is one of the main pieces of evidence for the 'Big Bang' theory of the expansion of our universe from some 'point' at 'time zero' around 14 billion years ago!

How do we know the universe is expanding? What is the red shift phenomena?

o The indigo should a dark blue, but on saving the graphic image, a few curious effects happened, sorry about that, but it doesn't detract from the explanation of the 'red shift'!

b) You should know that there is an observed increase in the wavelength of light from most distant galaxies.

o All the know galaxies of our universe appear to be moving away from each other in an ever expanding universe.

o Know that the further away the galaxies are, the faster they are moving, and the bigger the observed increase in wavelength.

o Know that this effect is called red-shift.o Some background science on the absorption spectrum diagram above (not sure

how much you need to know?). Stars are so hot that the atoms of the elements are in a gaseous state. Due to electronic changes in these hot atoms, certain specific frequencies of

visible light are absorbed by these atoms. Therefore, when you examine the visible light from distant stars, you get

black lines where that particular frequency has been absorbed by atoms ie that specific visible light frequency is missing.

The resulting 'picture', obtained by using an instrument called a spectrometer, is called the absorption spectrum, based on the visible region of the electromagnetic spectrum.

Some schools may have a simple mini version of a spectrometer, called a spectroscope, for you to look through, to give you an idea of what spectrum looks like.

In the diagram, I've tried to illustrate the idea using the spectral lines of the element hydrogen.

Hydrogen is the most abundant element in stars, but all the other elements absorb visible light waves, so the real absorption spectrum is much more complicated, but my diagram will do here to teach you the 'red shift' idea!

Reference to the 'red shift' emission spectrum diagram above. Hydrogen gives a series of specific spectral lines eg one in the red,

one in the green, several in the blue and many in the indigo and violet region (which are not shown).

The vertical black lines represent the absorption wavelengths/frequencies absorbed.

Each element has a finger-print pattern of lines, so the real spectrum is very complicated.

When the spectra from galaxies from a variety of distances away from Earth, a pattern was noticed and analysed (first by the astronomer Edwin Hubble in 1929) to show that the 'finger print'

pattern spectral lines of each element was the same BUT the wavelengths were all shifted to longer values (lower frequencies), hence the phrase 'red shift'.

The red-shift to longer wavelengths and lower frequencies, is indicated by the white arrows on the diagram.

I've only indicated the shift for the first two lines in the hydrogen spectrum.

c) Appreciate how the observed red-shift provides evidence that the universe is expanding and supports the ‘Big Bang’ theory (that the universe began from a very small initial point).

o Reference to the 'red shift' emission spectrum diagram above continued. Now, if bring in the idea of the Doppler effect, we can use this stellar (stars)

absorption spectrum as evidence to show that the universe is expanding. So instead of racing cars or trains, think stars, if the galaxies are moving

away from us, then the light waves will be stretched out over the millions/billions of miles so that the wavelengths get longer - which is in the red direction of the visible spectrum!

It appears, that no matter which direction you look, the galaxies are moving away from us because all the absorption spectrums are 'red-shifted', and, what is more, the further away the galaxy, the bigger the red shift.

This means that the galaxies are not only moving apart, but they are accelerating away from each other to the known visible limits of the universe.

This is the prime evidence for the 'Big Bang' theory of the expanding universe from some common point 14 billion years ago, that all the atoms ==> galaxies all have a common origin, and that point's age is calculated by working back from the equations representing the expansion of the universe!

The theory is, that 14 billion years ago there was some kind of enormous 'Big Bang' resulted in the release of huge amounts of energy in some form, that eventually formed atoms, stars and galaxies etc. and all the resulting galaxies are flying apart from this point of origin.

We have no idea about the origin of the 'Big Bang', all we can theorise is that our universe originated from this point (zero time!?).

Incidentally, if the universe was contracting and galaxies were hurtling towards us, we would observe a blue shift of decreasing wavelengths in the emitted light from them, but no so such effect has ever been seen.

d) Know that cosmic microwave background radiation (CMBR) is a form of electromagnetic radiation filling the universe.

o Know that this radiation comes from radiation that was present shortly after the beginning of the universe, soon after the 'Big Bang' started.

o This low frequency - long wavelength microwave electromagnetic radiation is detected from all parts of the universe.

o CMBR is associated with low temperatures as the young universe was cooling down. e) Appreciate that the ‘Big Bang’ theory is currently the only theory that can explain the

existence of CMBR.

Physics Unit P1 Topic 4 Waves and the Earth

4.1 Know that sound with frequencies greater than 20 000 hertz, Hz, is known as ultrasound. 4.2 Be able to describe some uses of ultrasound, including:

o a) sonar o b) communication between animals o c) foetal scanning

4.3 Be able to calculate depth or distance (d in m) from time (s) and velocity (m/s) of ultrasound

o using the formula: v = d / t, so rearranging gives d = v x t 4.4 Know that sound with frequencies less than 20 hertz, Hz, is known as infrasound. 4.5 Be able to describe uses of infrasound, including:

o a) communication between animals o b) detection of animal movement in remote locations o c) detection of volcanic eruptions and meteors

4.6 Know that seismic waves are generated by earthquakes or explosions 4.7 Revise any investigation you did into the unpredictability of earthquakes, using sliding

blocks and weight. 4.8 Be able to explain why scientists find it difficult to predict earthquakes and tsunami waves

even with available data. 4.9 Know that seismic waves can be longitudinal (P) waves and transverse (S) waves and

that they can be reflected and refracted at boundaries between the crust, mantle and core. 4.10 Be able to explain how data from seismometers can be used to identify the location of an

earthquake. 4.11 HT only: Be able to show an understanding of how P and S waves travel inside the

Earth including reflection and refraction. 4.12 Be able to explain how the Earth’s outermost layer is composed of (tectonic) plates and

is in relative motion due to convection currents in the mantle. 4.13 You must have an understanding of how, at plate boundaries, plates may slide past each

other, sometimes causing earthquakes.

Physics Unit P1 Topic 5 Generation and transmission of electricity

5.1 Be able to describe current as the rate of flow of charge and voltage as an electrical pressure giving a measure of the energy transferred.

5.2 Be able to define power as the energy transferred per second and measured in watts. 5.3 Be able to use the equation:

o electrical power (watt, W) = current (ampere, A) x potential difference (volt, V) o ie in the usual shorthand symbols P = I x V

o 5.4 Revise any investigation you did into the power consumption of low-voltage electrical

items. 5.5 Be able to discuss the advantages and disadvantages of methods of large-scale electricity

production using a variety of renewable and nonrenewable resources. o You must also be able to consider the reliability of different methods.o There are other general issues such as environmental impact - pros and cons for the

local community (eg jobs versus environmental damage, visual impact), how long will it take to build?, at what cost versus eventual power output?, planning delays etc.

o Ideally you would want to site a large fossil fuel/nuclear power station as near as possible to the major/bulk users AND in the case of coal, near a coal mine, since power line transmission involves wasted energy (see National Grid section).

o Large scale tidal and river/lake hydroelectric schemes and geothermal power plants all need very specific geographical locations.

o For safety reasons, nuclear power plants are sited in remote locations, often near the coast.

o Small scale power generation with solar cells and wind turbines can be sited anywhere, but larger wind farms need to be in a windy area eg on low hills or out at sea.

o Non-renewable energy sources These energy resources are finite and will run out

eventually, there are major associated environmental issues BUT at the moment, most of our useful energy is derived from them. These are historically, and to the present day, the major energy sources for large power stations.

e.g. Coal (mainly carbon), crude oil (certain hydrocarbon fractions), natural gas (mainly methane) and nuclear fuels (based on the metals uranium and plutonium).

o Renewable energy sources e.g. biofuels, geothermal, hydroelectric, solar radiation, tidal

changes, wave action, wind turbines Theoretically these energy resources will never run out and

generally speaking their environmental impact is not as great as non-renewables, but they only provide a small % of our energy needs at the moment and can be unreliable like the wind.

Most of these energy sources, apart from hydroelectric schemes and a few tidal barrage sites, are deployed on an experimental or small commercial scale.

Renewable energy resource technology should be the cheapest to run with no primary fuel costs.

o In some power stations an energy source is used to heat water. The steam produced drives a turbine that is coupled to an electrical

generator. ENERGY FLOW: chemical/nuclear energy (fuel) ==> heat energy (steam)

==> kinetic energy (turbine blades) ==> electrical energy (generator)

The non-renewable fossil fuels (coal, oil and gas) which are burned to heat water or air. The burning of fossil fuels leads to all sorts of pollution and environmental impact issues. The carbon dioxide produced by combustion is a 'greenhouse gas' implicated in global warming and climate change. In the smoke are acidic gases like sulfur dioxide and nitrogen oxides which are harmful to our health as air pollutants, and, by forming 'acid rain' wreak havoc with ecosystems (particularly aquatic ones and trees) and cause extra corrosion of stone and metal structures. It is possible to remove most of the sulfur from oil hydrocarbons before their use, and smoke from power stations can be treated with an alkali to remove acidic gases. There are other environmental issues eg the 'high price' dangers of coal mining, ugly open-cast coal mines, oil pipelines/tankers and oil spillage effects on wildlife.

In the UK, old coal/oil fired power stations are being replaced with cleaner less polluting gas fired power stations which have faster start up times - much easier to respond to higher/lower power demands.

Non-renewable fossil fuel power stations do provide a stable and reliable electricity supply, unlike some renewable energy resources which are distinctly unreliable eg wind power and solar power which depend on the weather.

The non-renewable nuclear fuels uranium and plutonium provide energy from nuclear fission (splitting atomic nuclei) and is used to heat water or carbon dioxide gas, either way, the hot fluid is used to make steam via a heat exchanger for safety reasons to drive turbines and generators. Environmental issues include how do we store, and where do we put, dangerous radioactive waste from nuclear power stations?, disasters such as the Chernobyl nuclear power plant explosion in Russia with its long term effects on people and the local flora (plants) and fauna (animals). Nuclear power stations may take over a decade to build and involve the most complicated technology of any means of power production. Safety standards must be exceptionally high and very costly.

Renewable Biofuels that can be burned to heat water to make steam to drive a turbine and generator. Biofuels are renewable energy sources and come in a variety of forms eg woodchips (trees or waste from timber products), alcohol (ethanol from fermenting sugar cane), biodiesel (from vegetable oil) and biogas (methane from anaerobic digestion of sewage waste) and are all derived from plant materials eg crops or bacterial digestion/decay of waste organic material. The theoretical 'carbon neutral' idea behind using biofuels is that the carbon dioxide released on burning is re-absorbed by plants and utilised in photosynthesis to create the next fuel crop. But, even though this sounds fine in principle, there are still environmental issues eg in Brazil and other countries, huge areas of ecological valuable natural rain forest (habitats, species rich) are being cut down to grow crops for biofuels.

o The flow of water and wind can be used to drive turbines directly. Know that renewable energy sources used in this way

include, but are not limited to, wind, waves, tides and the falling of water in hydroelectric schemes and all involve converting FREE kinetic energy into electrical energy using a generator. None of these schemes needs a fuel, or produces any kind of chemical pollution on the site, and all are 'green' in terms of not consuming fossil fuels ie carbon dioxide, but they may have quite an environmental impact. All these methods can contribute to National Grid of electricity supply.

Wind power - wind turbines: Wind turbine blades are driven by the kinetic energy of wind movement which in turn drive a generator (electrical energy). They are sited in clusters ('wind farms') on open land or out at sea (the latter is a more expensive location to erect the turbines) where, from surveys done, a commercial amount of wind blows! Wind turbine technology isn't cheap, but as more are built and designs improve, they are becoming more commercially more viable and the energy is free and maintenance costs are low. It takes a great many wind turbines to generate the same amount of electricity as a large scale power station. Some people object to what they see as 'visual pollution' or 'noise pollution' but at one time hundreds of windmills were a common sight in the countryside. There are several other problems too eg wind speed is variable and if it drops to zero, so does the power generation. Wind power generation is not capable of dealing with the high energy demands of peak times eg peak travel times. and cooking because unfortunately you cannot increase power production at all.

Wave power: One method of using wave movement is to use its kinetic energy of up and down oscillation to compress air in a funnel and tunnel the air through a turbine connected to a generator on the sea shore. It has not so far (as I know?) proved very successful. There are several problems eg variable wave height giving variable power output, storm damage is a regular risk. The initial cost is high, but bar storm damage, the running costs are low, there is no pollution and the energy is free.

Tidal power - hydroelectricity (i): Tides are caused by the gravitational pull of the moon and sun, and the flow of tides involving huge quantities of water, and a rise and fall in height of water of several metres. The incoming tide involves kinetic energy, but at the turn of high tide we now have a great store of gravitational potential energy (GPE), which on flowing back down is converted to kinetic energy. If this tidal flow can be controlled on a large scale and channelled through turbines connected to generators, then you effectively have a power station. This has been achieved by building a huge tidal barrage across a suitable estuary and building turbines and generators into the dam like structure. The incoming tide drives the turbines as does the controlled released of the huge amount of stored water (GPE) stored behind the barrage at high tide. Hydroelectric dam schemes are very costly to build needing a large capital investment and take a long time to build, but the energy is free and there is no pollution and maintenance costs are low. However, there maybe some environmental cost by disrupting the local ecosystems and wildlife and leisure/commercial craft on the river. Tides are reliable and times/heights can be accurately predicted but there periods of time when the water levels are similar on both sides, therefore little effective water flow and electricity generation. It is an advantage to store huge quantities of water that can be released at electricity peak demand times.

GPE ==> kinetic energy ==> electrical energy Hydroelectric power - hydroelectricity (ii): The

potential energy of a head of water (deep water) can be released by allowing the falling water to flow down through turbines connected to electrical generators. You need to build a dam to flood a valley and set the turbines and generators deep down in the dam's lower structure. The dam will hold back water from any river or stream running into the valley and the water supply fairly constant as long as it rains regularly, there maybe problems in a drought! It is very costly to build but there is no pollution and running costs are relatively low. It also has the advantage of delivering lots of power rapidly for peak demands of the National Grid by releasing more water through the turbines. However, there is a huge environment impact eg villages may have to be evacuated and rehoused, agricultural land and

wildlife habitats are lost. In more recent times more local small scale electricity generation schemes are being developed eg in remote areas using an Archimedes screw driven by river water to drive a turbine.

gravitational potential energy==> kinetic energy ==> electrical energy

Pumped storage systems - hydroelectricity (iii): A pumped storage system is way of storing extra energy (GPE) by linking to the National Grid in 'both directions'. Normally a hydroelectric power station works in one direction ie supplies the National Grid with electricity. In a pumped storage system, any excess electricity in the National Grid is used to run the generators and turbines in reverse, that is to pump water from a lower reservoir to the upper reservoir. At peak demand times, the extra stored water is released to generate additional electricity. So where does the excess electricity come from? Conventional fossil fuel or nuclear fuelled power stations operate most efficiently, and therefore most economically by running at a fairly high and constant level of power production ie it is inconvenient and inefficient to alternate between high and low rates of power production. However, through the night, power demand is at its lowest and so excess electricity is being generated. So, quite simply, the pumped storage system uses the surplus electricity at night to pump up and store water and release it when required the following day at peak demand times.

o 'Renewable' electricity can be produced directly from the Sun’s radiation.

You should know that solar cells can be used to generate electricity and should be able to describe the advantages and disadvantages of their use.

Solar cells (photovoltaic cells) produce 'small scale' electricity direct from sunlight energy, it is no good for a large scale electricity supply. Its free, but variable eg from cloudy days to bright sunny days, and of course it cannot work at night - so variable output is a problem, but it is being widely exploited in very sunny countries from eg Spain to African states. The technology eg installation is expensive, but getting cheaper and it is non-polluting when installed and runs off free energy with very low maintenance costs. One important advantage is that it easy to install on a small scale in remote areas not connected to the mains electricity supply. Lately, many people in developed countries are putting solar panels on their house roofs to generate electricity which adds to the electricity supply (National Grid) and reduces their own electricity bill. In developing countries it is a most important and convenient way of generating electricity on a local small scale in locations far from a national electricity supply.

o In some volcanic areas hot water and steam rise to the surface.

Know and understand that the steam can be tapped and used to drive turbines and this is known as geothermal energy.

The rising hot water and steam is used to drive a turbine which in turns a generator, again free energy and no pollution.

heat energy ==> kinetic energy ==> electrical energy Although there is little impact on the environment, it is quite costly to build for

the power you get, and there are a limited number of places where this is a convenient means of electrical power production. You can also use this geothermal energy from hot water/steam can be used to heat home directly

o The small-scale production of electricity may be useful in some areas and for some uses, eg hydroelectricity in remote areas, solar cells for roadside signs, remote telephone kiosks.

You should understand that while small-scale production can be locally useful because it is sometimes uneconomic to connect such generation to the National Grid.

o Using different energy resources has different effects on the environment and these effects include:

the release of substances into the atmosphere, the production of waste materials, noise and visual pollution, the destruction of wildlife habitats. Also, you should know and understand that carbon capture and storage is a

rapidly evolving technology. To prevent carbon dioxide building up in the atmosphere we can

catch and store it. Know that some of the best natural containers are old oil and gas

fields, such as those under the North Sea. The idea is to capture the carbon dioxide from fossil fuel burning

before it is released into the atmosphere and pump it to some suitable storage location.

Is it possible to feed the carbon dioxide to algae from which to derive a biofuel?

I do know that carbon dioxide from a fermentation process is fed into greenhouses to promote growth of crops like tomatoes! Can we do it on a bigger scale?

There are other ways to reduce carbon dioxide, principally by reducing electricity demand, so less fossil fuel is burned. You can reduce electricity demand in the home by insulation, better designed and more energy efficient appliances like washing machines, low energy light bulbs, turning off all devices/appliances not in use.

5.6 Be able to show an understanding of the factors that affect the size and direction of the induced current.

5.7 Revise any investigation into factors affecting the generation of electric current by induction.

5.8 Be able to explain how to produce an electric current by the relative movement of a magnet and a coil of wire

o a) on a small scale o b) in the large-scale generation of electrical energy

5.9 Know that generators supply current which alternates in direction. 5.10 Be able to explain the difference between direct and alternating current. 5.11 Know that a transformer can change the size of an alternating voltage. 5.12 HT only: Be able to use the turns ratio equation for transformers to predict either the

missing voltage or the missing number of turns. 5.13 Be able to explain why electrical energy is transmitted at high voltages, as it improves

the efficiency by reducing heat loss in transmission lines. o The National Grid consists of a vast network of pylons and cables (power lines)

insulated and suspended from these pylons.o All major power stations feed into the National Grid irrespective of their geographical

location and many are needed to service millions of users in homes, transport and industry right across the country.

o You see them stretching for miles and miles across the landscape to supply you, the consumer, very conveniently with a constant (well nearly!) supply of electricity to your city, town or village across the vast majority of the country.

o power station ==> step-up transformer ==> grid system ==> step-down transformer ==> user/consumer

o For a given power increasing the voltage reduces the current required and this reduces the energy losses in the cables.

o You should know why transformers are an essential part of the National Grid.o So that you can transmit (transfer) the very large quantities of electrical energy

needed you need to use, either, a very high current or a very high voltage or both. the four possible choices are (i) low current/low voltage, (ii) high current/low

voltage, (iii) low current/high voltage and (iv) high current/high voltage. (i) couldn't deliver what is needed, but (iii) is the actual choice.

So why is 'low current/high voltage' the desired choice for electrical power line transmission.

The greater the current flowing through a wire, the greater the heat generated, which in the context of power lines means waste heat energy, which is why (ii) and (iv) are not employed.

However, power = current x voltage, so to deliver a particular power rating, you can increase one of the two variables and decrease the other.

Therefore by using a very high voltage (eg 400 000 V, 400 kV) and relatively low current you maximise power transmission for the minimal heat loss of wasted energy.

o Use of these extremely high voltages (1667 x your domestic voltage of 240 V), means health and safety issues arise and you need lots of big ceramic insulators on pylons and transformers and lots of barbed wire to deter people from climbing up pylons!

o Now, (i) since the national power transmission uses 400 kV, you can hardly use this in the home, and (ii) generators themselves cannot deliver 400 kV, you need a way of increasing (for efficiency), and then decreasing (for safety), the voltage in power lines.

o A transformer is a means of changing an input voltage in one circuit, into another output voltage in a separate circuit.

At the power station end is a step-up transformer to increase the voltage for power line transmission.

At the user end is a step-down transformer, to reduce the voltage that is a safe level for factories, domestic homes, street lighting etc.

5.14 Be able to explain where and why step-up and step-down transformers are used in the transmission of electricity in the National Grid.

5.15 Be able to describe the hazards associated with electricity transmission. 5.16 Know that energy from the mains supply is measured in kilowatt-hours. 5.17 Be able to use the equation:

o cost (p) = power (kilowatts, kW) x time (hour, h) x cost of 1 kilowatt-hour (p/kW h)

5.18 Be able to show an understanding of the advantages of the use of low-energy appliances.

5.19 Be able to use data to compare and contrast the advantages and disadvantages of energy-saving devices.

5.20 Be able to use data to consider cost-efficiency by calculating payback times. 5.21 Be able to use the equation:

o power (watt, W) = energy used (joule, J) / time taken (second, s) o ie in the usual shorthand symbols P = E / t

Extra notes for sections 5.16, 5.17, 5.20 and 5.21 The amount of energy an appliance transfers depends on how long the appliance is switched

on and its power.o The quantity of electricity that is transferred ('used') in an appliance depends on its

power and how long you use it for ie time its switched on.o Energy is measured in joules (E in J) and power in watts (P in W)

1 watt = 1 J of energy transferred in 1 second (1 W = 1 J/s) Since a joule is a very tiny amount of energy, we often quote power in

kilowatts (P in kW). 1 kW = 1000 W = 1 1000 J/s

o A bulb might be quoted with a 50W rating (50 J/s), an iron might be quoted as having a 500W or 0.5kW power rating (500 J/s, 0.5kJ/s) and a three bar electric fire might have a 3kW power rating (3 kJ/s, 3000 J/s).

o However when dealing with large amounts of electrical energy its more convenient to think and calculate in kilowatt-hours (kWh).

1 kilowatt-hour = the amount of electrical energy that a 1 kW appliance uses in 1 hour.

In fact, in terms of the electricity use in a house, the term unit on your electricity bill means a kilowatt hour and the price will quoted as eg '9p per

unit', in other words you will pay 9p for every kilowatt-hour of electrical energy you use.

How to calculate the amount of energy transferred from domestic mains electricity using the formula:

o energy transferred by device = appliance power x timeo E = P x t o You will not be required to convert between kilowatt-hours and joules.o E is energy transferred in kilowatt-hours, kWho P is power in kilowatts, kW (1 kW = 1000 J/s)o t is time in hours, ho rearrangements: P = E/t and t = E/Po Also be able to use this equation when:

E is energy transferred in joules, J P is power in watts, W t is time in seconds, s

o The power formula triangle for the units of power in watts (W), units of energy in joules (J) and units of time in seconds (s).

Using the formula triangle: P = E/t and t = E/P

o The power formula triangle for the units of power in kilowatts (kW), units of energy in kilowatt-hours (kWh) and units of time in hours (h).

Using the formula triangle: P = E/t and t = E/P How to calculate the cost of using mains electricity given the cost per kilowatt-hour.

o You should know this includes both the cost of using individual appliances and the interpretation of electricity meter readings to calculate total cost over a period of time.

1 unit of electrical energy used = 1 kilowatt hour (kWh) (i) Units of electricity used = power (kW) x time (hours) (ii) Cost of electricity used = units x cost per unit

o For an individual appliance/device, combining (i) and (ii) gives for example cost (p) = power (kW) x time (hours) x electricity unit cost (p/unit)

o Examples of cost calculations: (for the sake of argument we'll call the price of electricity 12p per unit) (a) What is the cost per week of using a 40W light bulb for 36 hours in a

week? power = 40/1000 = 0.04 kW, units = kWh = 0.04 x 36 cost = 0.04 x 36 x 12 = 17.3p (3 sig. figs.)

It doesn't seem a lot, but throughout a house it soon adds up, so always switch unwanted lights!

(b) What is the cost of doing a single wash in a machine rated at 2.5 kW if it takes 30 minutes to complete the washing and spin drying cycle?

power 2.5 kW, time = 30/60 = 0.5 hour units = 2.5 x 0.5 cost = 2.5 x 0.5 x 12 = 15p

(c)(i) Ignoring the standing charge, what is the quarterly bill cost to a household that uses 650 units of electrical energy in three months?

cost = 650 x 12 = 7800p or £78 (c)(ii) If the family wants to cut the cost of the quarterly bill to £60,

what is the maximum number of units of electrical energy they can use?

cost = units x unit cost, so units = cost/unit cost = £60/12p = 6000/12 = 500 units

(d) How long could you run a 500 W plasma TV screen for 20p? cost (p) = power (kW) x time (hours) x electricity unit cost (p/unit) power = 500/1000 = 0.5 kW rearranging the equation

time = cost / (power x unit cost) time = 20 / (0.5 x 12) = 20 / 6 = 3.33 hours (3 hours 20

minutes)

Physics Unit P1 Topic 6 Energy and the future

6.1 Be able to show an understanding that energy is conserved. 6.2 Be able to describe energy transfer chains involving the following forms of energy:

o thermal (heat) o light o electrical o sound o kinetic (movement) o chemical o nuclear o potential (elastic) o potential (gravitational).

There are many types of energy - an alphabetical reminder list and examples of energy transfers.

o Chemical energy - chemical energy is 'stored' or 'bound up' in chemical

elements/compounds by virtue of their chemical structure. They can release energy when they react eg burning hydrocarbon fuels like petrol from crude oil, metabolising foods like fats and carbohydrates, discharging a charged car battery containing sulfuric acid solution and lead electrodes.

Since chemical energy is a form of stored energy, it does nothing until it is released and converted into another form of energy.

o Elastic potential energy - this is energy stored when some material is stretched or

compressed and the energy released when the constriction is released eg the wound up spring of a clockwork clock, a pulled elastic rubber band, stretched coiled metal spring, the compressed spring in a an animal trap, stretched bow before the arrow is released.

Since elastic potential energy is a form of stored energy, it does nothing until it is released and converted into another form of energy.

o Electrical energy - this is a flow of electrons in an electrical current, when an

electrical current flows, the electrons carry the energy. Electrical energy can be converted into light, heat or kinetic energy in electric motors.

o Gravitational potential energy (GPE) - an object or material possesses gravitational potential

energy by virtue of its higher position and can then fall or flow down to release the GPE eg winding up the weights on a clock, water stored behind a dam that can flow down through a turbine generator. Any object falling is converting GPE into kinetic energy (eg skier) and any object raised in height gains GPE (eg cable car).

Since gravitational energy is a form of stored energy, it does nothing until it is released and converted into another form of energy.

o Kinetic energy or movement energy (KE) - any moving object has kinetic energy and KE energy must be

removed from the object to slow it down eg a moving car, fired bullet

o Visible light energy (part of electromagnetic spectrum, like microwaves and infrared etc.)

- light is an example of electromagnetic radiation and the energy is carried by photons. All luminous sources by definition give out light eg the sun, light bulb, candle, fire etc. When light impacts on any material, the energy is absorbed eg sunlight shining on plant leaves in photosynthesis, light falling on the retina of our eyes.

Note that invisible infrared radiation is converted directly into heat eg warmth feeling in sunlight, standing by a fire, a toaster.

o Nuclear energy - this is energy released when atoms undergo a

nuclear reaction eg fission is when atoms split to form smaller atoms and fusion is when smaller atoms come together to form a larger atom. Both processes release huge amounts of nuclear energy. This energy can be harnessed to power steam turbine generators to drive generators producing electricity.

o Sound energy - this is energy carried by the vibrations of sound waves in a

medium usually air, but can be liquids like water or solids like iron. Noise from loudspeakers, squealing brakes of a car, using your vocal chords!

o Thermal energy (heat energy) - the hotter an object, the more thermal/heat energy the material

contains/holds and hot objects can release heat energy to the cooler surroundings. Heat energy can only flow from a higher temperature region to a lower temperature region ie from hot objects to cold objects.

a) Know and understand that energy can be transferred usefully from one form to another, or stored, or dissipated, but energy cannot be created or destroyed.

o This is the law of conservation of energy.o However, energy is only useful if it can be converted from one form to another.o Examples - from a suitable energy source ==> useful form (plus waste in most cases)

When a gun fires chemical energy is converted into heat energy, sound energy, light energy and mainly kinetic energy. When the bullet embeds itself into some material the kinetic energy of movement is converted into some sound energy, but mainly heat energy.

Photovoltaic solar panels convert light energy into electrical energy.

We use a large number of electrical devices in the home eg

TV converts electrical energy into useful light and sound, but some waste heat

A charged mobile phone battery converts chemical energy into electrical energy, which in turn is converted into useful light and sound energy.

Wind turbines convert kinetic energy into electrical energy b) Know and understand that when energy is transferred only part of it may be

usefully transferred, the rest is ‘wasted’. c) Know and understand that wasted energy is eventually transferred to the

surroundings, which will become warmer.o Appreciate that the wasted energy becomes increasingly spread out and so becomes

less useful.

6.3 Be able to show an understanding of how diagrams can be used to represent energy transfers.

o

o 6.4 Be able to apply the idea that efficiency is the proportion of energy transferred to useful

forms to everyday situations (see also diagram above and below). o Devices eg industrial machines, household appliances, light bulbs etc. can only be

useful if they can efficiently transform one form of 'source' energy ('total input') into an appreciable percentage of a 'useful' energy ('useful output').

o Such devices should be designed to 'waste' as little energy as possible, the less waste energy, the greater the efficiency of the device.

o See the energy flow diagram and efficiency formula 'triangle' above and the calculation of efficiency and Sankey diagram further down the page.

o It should be pointed out that virtually no device is 100% efficient, there is no such device as a perfect machine.

One of the most efficient 'energy converters' is an electric heater were nearly all the input electrical energy is converted into useful output heat energy

It is sometimes stated that an electrical heat is 100% efficient, BUT if the electric bar is glowing and visible, then there must be some energy loss as light.

o Whether of not the energy outputs are useful or waste, most of the energy input in a device ultimately ends up as heat energy.

o The most useful energy sources are in a sense 'highly concentrated' like a battery or a fuel like petrol, but as the energy is used you cannot recover the waste energy - it has been dissipated to the surroundings and become useless heat energy in this 'diluted' form.

o You should be able to use a Sankey diagram to calculate the efficiency of an appliance.

From a Sankey diagram (below) you can see quite clearly in a visual way what happens to the energy input into a device ie what proportion of energy was useful and how much energy was wasted.

The greater the width of the 'arrow' the greater proportion of energy it represents.

An electric motor illustrates the idea of a Sankey diagram. You will find an electrical motor in devices such as an electric drill, washing

machine, food mixer, electric car etc. etc. A lot of our lives runs on electrical power!

total energy in = total energy out = T% = 100% = K% + S% + H% This electric motor would have an efficiency of 56% useful energy out as

kinetic energy with losses of 17% sound from friction-vibration and 27% heat energy loss from moving parts friction or warm electrical wiring in the motor.

In this example the numbers are easy, but whatever the numbers are, from the Sankey diagram, you need to be able to get to the proportion of useful energy and covert it to a percentage of the total energy input.

6.5 Be able to use the efficiency equation: (useful energy transferred by the device) o % efficiency = (useful energy transferred by the device) x 100 / (total energy

supplied to the device)

o 6.6 Be able to demonstrate an understanding that for a system to be at a constant

temperature it needs to radiate the same average power that it absorbs. 6.7 Revise any investigation you did into how the nature of a surface affects the amount of

thermal energy radiated or absorbed. o a) All objects continuously emit and absorb infrared radiation from their surface,

whatever their temperature. o b) The hotter an object is the more infrared radiation it radiates in a given time, the

higher the temperature of the material, the more intense is the infrared radiation. An object that is hotter (higher temperature) than its surroundings will emit

more radiation than it absorbs and an object that is cooler than its surroundings will absorb more radiation than it emits.

You notice this effect in bright sunlight by feeling the warmth on your hand or standing near a fire.

When an object cools down to the same temperature as its surroundings emitted infrared radiation equals the absorbed heat radiation.

o c) Dark, matt surfaces are good absorbers and good emitters of infrared radiation eg rough black surfaces.

Solar panels for hot water comprise of pipes carrying water to be heated set under a black surface to efficiently absorb the infrared radiation from the Sun. You can even just use matt black painted water pipes. You may even have a silvered surface under the pipes so more infrared ins reflected onto the black surface rather than becoming waste heat radiation. The pipes are made of copper which allows efficient conduction of the surface heat energy to the incoming cold water., so the hot water can be used as part of the households domestic heating or washing etc.

o d) Light, shiny surfaces are poor absorbers and poor emitters of infrared radiation eg white gloss paint, silver surface used in vacuum flask ('thermos flask').

o e) Light, shiny surfaces are good reflectors of infrared radiation, this maybe to keep heat in to keep things warm or to minimise heat radiation in to keep things cool eg a vacuum flask.