PHYSICS 1 ENERGY AND ELECTRICITY RADIATION AND THE

PHYSICS 1 ENERGY AND ELECTRICITY & RADIATION AND THE UNIVERSE

ENERGY & ELECTRICITY

Heat Transfer Heat is a type of energy which will flow from a warmer area to a colder one. The bigger the temperature difference the faster heat is transferred. The bigger the surface area, the more waves can be emitted from the surface, so the quicker the transfer of heat. Heat is transferred in three different ways: RADIATION CONDUCTION CONVECTION

Heat Radiation Heat radiation can also be called infrared radiation. It is when heat moves around in electromagnetic invisible waves. It can carry energy through anything as it doesn’t need particles to move. • dark matt colours absorb and emit much more radiation • light shiny colours will reflect nearly all the radiation That is why we get: Matt black solar hot water panels that easily absorbs a lot of heat and the shiny inner surface to keep absorbed heat in. Silver survival blankets that help stop their body heat radiating away, which could save someone’s life. all objects above absolute zero are continually emitting and absorbing heat radiation • hot objects: emit more infra red than it absorbs • cold objects: absorb more infra red than it emits • the smaller the volume/mass the faster the temperature change • the larger the surface area the faster the rate of heat transfer • the larger the temperature difference to the surroundings the faster the rate of heat transfer

Heat Conduction of heat is when vibrating particles collide and pass on their extra kinetic energy. It occurs mainly in solids. • Metals are good conductors of heat because they have electrons which can move freely. • Poor conductors of heat like wood and plastic are called insulators. • Particles are involved and needed for conduction.

Heat Convection of heat occurs when the more energetic particles move from the hotter region to the cooler region and take their heat energy with them. Convection currents are all about changes in density. It only happens in liquids and gases as the particles are needed to move around. We can show a convection current using a cold beaker of water, solid lump of potassium permanganate (coloured crystal) and a heat source. 1) Particles are heated and gain kinetic energy, causing them to spread out and expand. 2) This means there is more distance between them making them less dense. 3) Reduction in density means the hotter air rises above the denser cooler air, moving it out of the way and making it fall towards the area being heated. 4) The hot air is receiving less heat to loses kinetic energy causing it to contract making it more dense. 5) As it is more dense it sinks back down while the cold air being heated rises.

Thermos Flask The thermos flask is the ultimate in insulation! 1) Stopper is made out of plastic and filled with cork or foam to reduce any heat conduction through it. 2) Outer plastic or stainless steel case. 3) Outer layer of glass coated with reflective material to keep heat loss by radiation to a minimum. 4) Vacuum between two walls stops all conduction and convection through the sides. 5) Inner layer of glass coated with reflective material. 6) Insulating foam supports the bottle and minimizes heat conduction to or from the outer glass bottle. 7) Additional insulation reduces heat losses and cushions flask against impacts.

Energy Transfer There are nine types of energy: Electrical Energy - when a current flows Light/Radiant Energy - from the sun, light bulbs, etc Sound Energy - released by vibrating objects Kinetic/Motion Energy - anything that’s moving has it Nuclear Energy - released only from nuclear reactions Thermal Energy - flows from hot objects to colder ones Gravitational Potential Energy - possessed by anything which can fall Elastic Potential Energy - stored in stretched or squashed objects Chemical Energy - possessed by foods, fuels, batteries, etc Two Types of Energy Conservation 1) “Energy Conservation” is about using fewer resources because of the damage they do and they might run out. 2) “Principle of the Conservation of Energy” says that energy can never be created or destroyed, it is only ever converted from one form to another.

Efficiency = Useful Energy Output Total Energy Input • Useful devices are only useful because they can convert energy from one form to another. • Some of the useful input energy is always lost or wasted. • The less energy that is wasted the more efficient the device is. Some devices are more efficient than others, but that’s not all that matters: 1) initial cost 2) running cost, including energy efficiency 3) how often will it need repairing/replacing? 4) ease of use, suitability for the job 5) appearance, how it looks

Energy Transformations All types of energy are measured in joules! • Electrical devices convert electrical energy into sound, light, heat, etc. • Batteries convert chemical energy to electrical to run electrical devices. • Electricity generation always involves converting forms of energy into electrical energy. • Gravitational and elastic potential energy always get converted into kinetic energy first.

Sankey Diagrams – Energy Transformation Diagrams The thickness of the arrow represents the amount of energy • The idea of Sankey diagrams is to make it easy to see how much of the input energy is being usefully made use of compared with how much is being wasted. • The thicker the arrow the more energy it represents. • You can have either a little sketch or a properly detailed diagram where the width of each arrow is proportional to the number of joules it represents.

Cost of Electricity Number of Units(k. Wh) = Power(kilowatts) x Time(hours) Cost = No. of Units x Price per Unit • An electricity meter counts the number of units used. • A unit is known as a kilowatt hour or k. Wh. • A kilowatt hour is the amount of electrical energy used by a 1 k. W appliance left on for one hour.

Energy Efficiency at Home • Cavity Wall Insulation: foam put into the gap between bricks reduces convection and radiation across the gap. • Loft Insulation: a thick layer of fiberglass wool laid out across the whole loft floor reduces conduction and radiation into the roof space from the ceiling. • Draught Proofing: strips of foam and plastic around doors and windows stop draughts of cold air blowing in, they reduce heat loss due to convection. • Double Glazing: two layers of glass means more radiation reflected back and the air gap between the layers reduces conduction. • Thermostatic Radiator Valves: these simply prevent the house being over warmed. • Hot Water Tank Jacket: lagging suck as fiberglass wool reduces conduction and radiation. • Thick Curtains: bits of cloth over the window to reduce heat loss by conduction and radiation. • Cheaper methods of insulation tend to be more cost effective than expensive ones. • The ones that save the most money each year is considered the most effective.

National Grid Electricity Gets Around via The National Gird • The national grid takes electrical energy from the power stations to just where it’s needed in homes and industries. • It allows power to be generated anywhere on the grid and then be supplied anywhere else on the grid. • To transmit the huge amount of power needed, you need either a high voltage or a high current. • The problem with a high current is that you lose loads of energy through heat in the cables. So it’s much cheaper to boost the voltage up really high and keep the current very low. • Transformers have to step the voltage up at one end, for efficient transmission and then bring it back down to safe, usable levels at the other end. • The voltage is increased using step up transformers and reduced at the consumer end using a step down transformer.

Power Stations Nuclear Radioactive minerals like uranium are formed naturally in the ground, we which we then mine. A nuclear reaction called nuclear fission spit nuclei producing heat. Advantages • A small amount produces a lot of energy • Doesn’t give off atmospheric pollutants Disadvantages • Nuclear reactors are expensive to run • Nuclear waste is highly toxic needs to be safely stored for thousands of years • Leakages can have devastating impact on people and the environment. • Nuclear radiation damages cells. • Plutonium is a waste product and can be used to make nuclear bombs. Non Renewable Energy Resources They are: coal, oil, natural gas and nuclear fuels. Coal is formed from fossilized plants that consists of carbon. Oil is a carbon based liquid formed from fossilized sea creatures. Natural Gas is mainly methane trapped between rocks under the earth’s surface. They will all run out one day. They all do damage to the environment. But they provide most of our energy. Advantages • Ready made fuel. Quite cheap to extract and convert into energy. Produces a lot of heat. Disadvantages • Takes millions of years to form, so it will eventually run out. Releases carbon dioxide which increases the greenhouse effect which causes global warming, nitrogen oxide and sulfur dioxide which causes acid rain.

Renewable Energy Sources They Are: wind, waves, tides, hydroelectric, solar, geothermal These will never run out, most of them do little damage to the environment. But don’t provide much energy. Using Water Hydro Electric They use the kinetic energy by releasing water behind a dam, the water rushes down through tubes inside the dam driving the generator. But they are expensive to build and destroy habitats. Wave Power Wave converters are located around the coast and as waves come in to the shore they provide up and down motion which can be used to drive a generator. However, they are fairly unreliable, spoil the view and hazardous to boats. Tides Tidal barrages are big dams built across river estuaries with turbines in them. As the tide comes in it fills up the estuary of a height of several meters. This water can then be allowed out through turbines at a control speed also driving the turbines on the way. But they prevent free access by boats, spoil the view and alter the habitat. Solar Energy from sunlight is captured in solar cells which convert it directly into electricity. But it’s very expensive and only works when there is sunlight. Wind turbines have big blades and as the wind blows it spins, transferring kinetic energy which drives the generator. However, it’s noisy and spoil the view, also the amount of electricity made depends on the strength of the wind. Geothermal The natural heat of the earth can be used by pumping cold water underground and it comes out as steam, to drive a generator. However, it only works in areas of volcanic activity.

RADIATION & THE UNIVERSE

Electromagnetic Waves • Electromagnetic radiation travels as electromagnetic waves, they transfer energy from one place to another with moving any matter. • wavelength: distance from on peak to the next • frequency: how many complete waves there are per second passing a certain point, measured in hertz (Hz) • amplitude: height of the wave from midline to peak • speed: how fast it goes EM waves with different wave lengths or frequencies have different properties. We group them into seven basic types. The higher the frequency the lower the wavelength. They all move at the same speed. wave speed(m/s) = frequency(Hz) x wavelength(m)

EM Radiation • The different wavelengths of EM radiation interact differently with matter. • What happens to the radiation depends on what the substance is, what the surface of the substance is like and wavelength of the radiation. • Transmitted: just pass through the substance • Reflected: bounce back • Absorbed: the energy of the wave is transferred to the matter, this can make the substance absorbing it get hotter or set up a tiny alternating current with the same frequency as the EM wave If the angle of incidence is: • less than critical angle most of the light passes out but a little bit of it is internally reflected • equal to critical angle the emerging ray comes out along the surface and there is a quite a bit of internal reflection • greater than the critical angle no light comes out, it’s all internally reflected – total internal reflection

EM Waves Uses & Dangers In general, waves with lower frequencies are less harmful than high frequency waves. This is because the energy of any electromagnetic wave is directly proportional to its frequency. So higher frequency waves have more energy and it’s the energy of the wave that does damage. Less Dangerous • Visible light isn’t harmful unless it’s really bright, staring at the sun could damage your eyes. • Infrared can cause burn or heatstroke. • Some wavelengths of microwaves are absorbed by water molecules and heat them up. If the water happens to be in your cells, you might start to cook. More Dangerous • The sun’s rays include ultraviolet radiation which damages the DNA in your cells, so the more time you spend in the sun, the more chance of you getting skin cancer. • X rays pass through flesh but not through denser material like bones or metal. They can cause mutations which can lead to cancer. Uses • Radio waves are used for communication, long wave radio can be transmitted to long distances because long wavelengths can bend around the curved surface of the Earth. Very short wave lengths, to get reception you must be in direct sight of the transmitter. But short wave radio signals can be receives at long distances as they are reflected from the ionosphere, an electrically charged layer in the Earth’s atmosphere. • Communications to and from satellites uses microwaves, you need to use microwaves which can easily pass through the Earth’s watery atmosphere. • Optical fibers can carry data over long distances as pulses of light or infrared radiation, the waves bounce off the sides of the inner core. The wave enters one end and is reflected repeatedly until it reaches the other end. They use total internal reflection.

Analogue & Digital Signals Information is converted into signals. Information, such as sounds and pictures, is converted into electrical signals before it’s transmitted. It’s then sent long distances down telephone wire or carried on EM waves. Analogue Signals • the amplitude and frequency vary continuously • it can take any value in a particular range • dimmer switches, thermometers, speedometers are analogue devices Digital Signals • they are coded pulses and can only take two values: on/off, true/false, 0/1 • switches, digital clocks, meters are digital devices • Both digital and analogue signals weaken as they travel, so they need to be amplified along their route. They also pick up interference or noise from electrical disturbance or other signals. • Digital signals have better quality as the information received is the same as the original, if you receive a noisy digital signal it’s pretty obvious what it’s suppose to be but it’s difficult to know what a original analogue signal would have looked like

Radioactivity Each element has 1 or 2 isotopes that are stable, the others are radioactive, the nucleus is unstable so it decays (breaks down) and emits radiation. • each nucleus decays quite spontaneously in its own good time at random, it’s unaffected by physical conditions like temperature • when it does decay it spits out one or more of the types of radiation: alpha, beta, gamma • in the process the nucleus often changes into a new element • causes ionization by bashing into atoms and knocking electrons of them – the further the radiation can penetrate before hitting an atom and getting stopped, the less damage it will do along the way and so the less ionizing it is Alpha Particles are Helium Nuclei • relatively big, heavy and fairly slow moving • don’t penetrate far into materials but are stopped quickly • because of their size its strongly ionizing • electrically charged so are deflected by electric and magnetic fields Beta Particles are Electrons • is an electron which has been emitted from the nucleus of an atom when a neutron turns into a proton and an electron, so for every beta particle emitted the number of protons in the nucleus increases by one • move quite fast and small • penetrate moderately before colliding and are moderately ionizing • negatively charged so are deflected by electric and magnetic fields Gamma Rays are Electromagnetic Waves • no mass, they are just energy • penetrate a long way into materials without being stopped • weakly ionizing as they tend to pass through rather than collide with atoms • have no charge so they’re not deflected by electric or magnetic fields

Half Life Radioactivity of a Sample Decreases Over Time • each time an unstable nucleus decays and emits radiation, that means one more radioactive nucleus isn’t there to decay later • as more unstable nuclei decay, the radioactivity of the source as a whole decreases – so the older a radioactive source is the less radiation it emits • how quickly the activity decreases varies a lot • the problem with trying to measure this is that the activity never reaches zero, which is why we have to use the idea of half life to measure how quickly the activity decreases. Half Life is the time taken for half the nuclei now present to decay • a short half life means the activity falls quickly as lots of the nuclei decay quickly • a long half time means the activity falls more slowly as most of the nuclei don’t decay for a long time, they just sit there basically unstable Half life is the time taken for the count rate to halve, you can work out the half life of a sample by monitoring its count rate (the number of atoms which decay per minute). Then plot a graph of count rate against its time.

Radiation Uses & Risks Long Half Life For Devices That Have To Last • sterilizing machines in hospitals use gamma radiation to kill bacteria on medical instruments • smoke detectors use a weak source of alpha radiation to ionize the air between two electrodes Medical Tracers • a source which emits beta or gamma radiation is injected into the patient, the radiation penetrates the body tissues and can be detected externally Industrial Tracers • if your looking for a leak in an underground pipe squirt gamma ray source into the pipe and go along the outside with a detector, if there’s a crack the source will collect outside the pipe and your detector will show extra high radioactivity Radiation Harms Living Cells • beta and gamma can penetrate the skin to reach the delicate organs inside the body, their radiation mostly passes straight out without much damage – more hazardous outside • alpha can’t penetrate the skin but once inside they do all their damage in a very localized area • if radiation enters your body it will collide with molecules in your cells this causes ionization which damages or destroys the molecules • lower doses damage without killing the cell but cause a rise to mutant cells which divide uncontrollably – this is cancer • higher doses kill cells completely causing radiation sickness • the extent of the harmful effects depend on how much exposure you have to the radiation, its energy and penetration It is used to treat cancer too Radio therapy kills the cancer cell and stop them dividing. This involves a high dose of gamma rays directly zapping the cells in the tumor which minimizing the dose to the rest of the body.

Origin of the Universe Light From Other Galaxies Is Red Shifted • when we look at light from distant galaxies we find that the frequencies are all slightly lower, they’re shifter towards the red end of the spectrum – this is called the red shift • it is like a sound is lower pitched when it is moving away from you – this is called the Doppler Effect • measurements of the red shift suggests that all the galaxies are moving away from us • more distant galaxies have greater red shifts than nearer meaning they are moving faster, this proves evidence that the whole universe is expanding Bang Theory – Universe Is Expanding • all matter and energy in the universe must have been compressed into a very small place, then it exploded and started expanding and the expansion is still going on now • the age of the universe can be estimated from the current rate of expansion, we think the Big Bang happened 13. 7 billion years ago