AQA Physics Unit 1

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All objects emit and absorb infrared radiation. Infrared radiation is a type of electromagnetic wave, and so does not need a medium to travel through. A type of picture called a thermogram can be used to show how much infrared radiation an object is emitting, because it is not always possible to tell whether it is emitting radiation just by looking at it.

When an object is warmer than its surroundings, it will emit infrared radiation; if an object is cooler than its surroundings, it will absorb infrared radiation from the surroundings. The hotter an object is, the more infrared radiation it will emit.

The surface of an object also affects how much infrared radiation it will absorb and emit. Dark, matt surfaces absorb infrared radiation better than light, shiny surfaces. This is why houses in hot countries are painted white, and why the inside of a vacuum flask is shiny.

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P1.2- Solids, Liquids and Gases

Solids

• Particles packed close together, in a regular pattern
• Held by attractive forces between them and vibrate about their points
• Fixed shape and volume

Liquids

• Particles close, in an irregular pattern
• Still attracted to each other
• No fixed shape but fixed volume

Gases

• Particles too far apart to attract each other
• No fixed shape, no fixed volume

As temperature increases, the speed of the particles also increases. They take up more space, and the substance expands. It changes state of matter. This is kinetic theory.

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P1.3- Conduction

Heat energy is transferred through solids by conduction. The particles are always vibrating, but do so more when the object is heated. They knock into neighbouring particles, causing them to vibrate and knock into their neighbouring particles.

Conduction in metals

Metals are very good conductors of heat becuase in metallic bonding, there are free electrons that are free to move through the metal. When they gain kinetic energy through heating, they can take the energy much further through the metal than a non-metallic object could transfer it from atom to atom.

Conductors and Insluators

Metals are good thermal conductors becuase energy is conducted through them easily. Materials that are not very good at conducting are called thermal insulators- for example, wood and plastic. This is because the pattern is less regular and they have no free electrons.

A conductor feels cold to the touch because it conducts energy away from the skin, and vice versa for an insulator. Solids are the best conductors; gases are the best insulators.

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P1.4- Convection

Fluids are poor thermal conductors, but because their particles are free to move, they are still able to conduct energy. Convection is when moving particles carry energy from one place to another.

When particles in one part of a fluid gain more energy, the particles in that area move around more and take up more space. The density of this area is lower, and because of this is rises. The cooler areas nearby are more dense and sink down, closer to the energy source. This movement is called a convection current

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P1.5- Evaporation and Condensation

Evaporation

In a liquid, the particles do not all have the same amount of energy. Some are able to escape from the surface of the liquid, and eventually, like a puddle on the ground, all the particles will have escaped from the surface, leaving behind no liquid. This is evaporation. There are some factors that affect the rate of evaporation:

• Increase the flow of air (prevents the particles from falling back into the liquid)
• Add energy by heating the liquid (so more particles are able to escape from the liquid)
• Increase the surface area of the liquid (so more particles are at the surface of the liquid)

Condensation

Condensation is the reverse of evaporation. Particles in a gas have more energy than the particles in a liquid, but if they lose they energy, they are forced to slow down and get closer. They condense to form a liquid again.

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P1.6- Energy Transfer by Heating

Energy is transferred to or from an object until both it and its surroundings are the same temperature. This rate can be changed in a variety of ways:

• Temperature difference- When the difference in temperature between the object and its surroundings is large, the energy transfer will occur faster, and vice versa
• Size and shape- An object with a larger surface area will transfer energy to its surroundings faster than an object of the same volume with a smaller surface area because the energy from the particles is closer to the surface so can escape more easily
• Material- A good thermal conductor will transfer energy more quickly than a similar object that is a thermal insulator
• Contact material- If the object is in contact with a good thermal conductor, the object will transfer the energy away faster. The opposite will occur with a thermal insulator
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P1.7- Comparing Energy Transfers

Animals in hot countries tend to have large surface areas so that a good blood supply can take heat to the surface of the skin and allow it to leave the body. Animals in cold countries have the opposite, with much smaller surface areas to retain heat.

Design for energy transfer

Radiators- long and thin to maximise surface area; bent fins at the top to direct convection current into the room rather than up the wall

Vacuum flasks- inner and outer surfaces are silvered to reflect infrared radiation; vacuum between surfaces to prevent conduction and convection; bottle held in place by poor conductors; screw cap made of a good insulating material

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P1.8- Heating and Insulating Buildings

Cavity Walls

There are three main parts to a cavity wall: the outer made of bricks, the inner made of lightweight concrete and a cavity between the two. The inner wall is made of a very poor conductor. The cavity (made of explanded polystyrene or a similar insulating material with small pockets of air), prevents convection currents being set up and allowing heat to leave the building. Double glazed windows work in a similar way, but with a vacuum between two panes of glass.

U-Values

Different parts of a building will conduct energy at different rates. We can measure the rate of losing energy for each part using a U-value. The higher the U-value, the faster energy is transferred. A material with a low U-value is a very good insulator.

Builders try to construct buildings with as low U-values as possible.

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P1.9- Solar Panels and Payback Time

Solar Panels

Solar panels absorb radiation from the sun and transfer the energy to heat water. A natural convection current occurs in the pipes connected to the solar panel. Solar panels even work on a cold day because the sun constantly gives out infrared radiation. Only a cloudy day will stop the panel from working. Solar panels are black in colour because dark, matt surfaces absorb infrared radiation well, so it makes the panel as efficient as possible.

Payback Time

Some methods to reduce the amount of energy used in a house cost money. To figure out whether it is worth investing in methods such as solar panels, loft insulation or double glazed windows, the payback time needs to be calculated. The payback time is the cost divided by savings per year, giving an answer in years. The method with the shortest payback time, or lowest amount of years, is the most cost-effective.

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P1.10- Specific Heat Capacity

The specific heat capacity of a material is the amount of energy is takes to heat 1kg of the material by 1 degree. The units are J/kg degrees. The equation to work out the amount of energy needed to heat an object is

energy = mass x specific heat capacity x temperature change

If you know the amount of energy transferred, the mass and the change in temperature, the same equation can be rearranged to work out the specific heat capacity

specific heat capacity = energy transfer / (mass x temperature difference)

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P1.11- Uses of Specific Heat Capacity

Different materials have different uses depending on what their specific heat capacity is.

Water- central heating systems due to its high specific heat capacity. It can transfer a lot more energy than a liquid with a lower specific heat capacity.

Concrete- electric storage heaters because it has a high specific heat capacity and can release energy slowly during the day, but is easier to maintain than water. Concrete can store a lot of energy and the temperature can be quite low and still hold the energy.

Oil- oil-filled radiators because it has a high specific heat capacity and can provide a gentle, steady heat. The energy in the oil is transferred to the surface of the radiator by convection

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P1.12- Understanding Energy

Energy takes many forms, such as heat, light, sound, kinetic, and electrical. It can be stored in many ways, including:

• chemical energy- stored in food, fuel and batteries
• nuecleur energy- stored in the nucleus of atoms
• elastic potential energy- stored in anything squashed or stretched (eg rubber band)
• gravitational potential energy- stored in any object higher than its surroundings

Many appliances transfer energy from one of these forms to another- for example, a kettle transfers electrical energy into sound and heat energy. Most appliances transfer energy into more than one form, like the kettle example. One of these energy forms will be useful, like the heat energy; the others will be wasted energy, like the sound energy from the kettle.

The amount of energy at the beginning of these transfers is always equal to the amount of energy at the end, even if some of it is wasted, as energy cannot be created or destroyed. This is the law of conservation of energy.

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P1.13- Useful Energy and Energy Efficiency

When an appliance transfers energy, some is useful and some is wasted. For example, a lightbulb may transfer 1500J of electrical energy into 300J of light energy, and 1200J of heat energy to its surroundings.

With this information we can work out the efficiency of the lightbulb. The equation is

efficiency = useful energy transferred / total energy supplied

The answer will be in joules, but can be converted to a percentage by multiplying by 100.

All electrical appliances have an energy efficiency rating. The label shows how much energy you would expect the appliance to use within a year, and the appliance is graded in one of seven categories, from A to G.

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P1.14- Using Electricity

Different types of electrical appliances have various advantages and disadvantages. For example, a battery powered radio will run for a long time, but will eventually need its batteries replacing. A clockwork radio does not suffer this problem, but does have to regularly be wound up in order to work.

The amount of energy an appliance produces per second is called its power. Power can be measured in one of two ways: joules per second, or watts. One joule per second is the same as one watt. 1000 watts is 1 kilowatt (or kW).

The equation to work out energy transfer or rearrange to work out power is

energy transferred = power x time switched on for

Many electrical appliances have a power rating to show how much power is needed to run them.

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P1.15- Paying for Electricity

In the equation

energy transferred = power x time

if the power is given in kilowatts and the time in hours, the energy is measured in kilowatt-hours. On an electricity bill, kilowatt-hours are called units of electricity.

The amount of electricity used is recorded by a meter, and is paid for per kilowatt-hour or unit. You can work out the cost of the electricity used by an appliance using the following equation:

cost = energy transferred x cost per unit

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P1 Part 1 Catch Up

• The transfer of energy from a hot object to a cool object by electromagnetic waves in infrared radiation. Dark, matt surfaces absorb emit and absorb infrared radiation better than light, shiny surfaces
• The three states of matter (solid, liquid and gas) are explained by the kinetic theory of particles
• Metals conduct energy well due to free electrons. Other solids do not, and are thermal insulators
• Liquids conduct energy as their particles are free to move. Convection currents develop when dense, cooler fluid falls and less dense, warmer fluid rises
• Particles in liquids use energy to escape from the surface (called evaporation)
• The rate of energy transfer increases with surface area, temp difference and materials
• Animals in hot countries are adapted to dissipate energy quickly, unlike those in cold countries
• Buildings can lose energy by conduction, convection and radiation. Insulation helps prevent this. The rate of energy loss is called its U-value
• Solar panels provide warm water when infrared radiation from the sun is transferred to water in the pipes
• The amount of energy required to heat one kilogram of a substance by one degree celsius is its specific heat capacity
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P1.16- Generating Electricity

Most electricity in the UK is generated by using an eergy source to heat water. The energy source is usually fossil fuel, biomass or the sun.

Thermal Power Station

In a thermal power station, a fossil fuel is burned to heat the water above it. The water turns to steam, and is used to turn the turbines. This in turn rotates the generator, creating electricity. The steam condenses and returns to the fossil fuels, where it is heated again and this cycle repeats, using more fossil fuels.

Geothermal Power

In volcanic areas of the world, geothermal energy cna be used to generate electricity. Steam rises to the surface of the earth from below, where there are very hot rocks, and the steam is collected and sent to a power station to frive the turbines. Geothermal energy has no fuel costs, but money must be spent on building and maintaining the power station. These power stations can be started up and stopped quite quickly and easily.

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P1.17- Fossil Fuels and Carbon Capture

Coal, oil and natural gas are all fossil fuels. They all produce carbon dioxide when burned. Natural gas has a very short start up time compared to the other two, which allows the power stations to cope with sudden increase and decrease in demand.

In every fossil fuel power station, fuel is burnt to produce a steam, which turns the tubrines. The burning of the fossil fuels produces pollutants, which are released into the atmosphere as waste products.

The main gas produced by fossil fuel combustion is carbon dioxide, which contributes to global warming

One way of reducing the amount of carbon dioxide that gets released into the atmosphere is by using carbon capture. This is when the carbon dioxide is trapped before it can enter the atmosphere, and is then stored in old oil and gas fields, such as those under the North Sea.

This process could reduce the amount of carbon dioxide that a fossil fuel power station releases by around 80%. However, this is a new and largely untested technology, and there are currently no fossil fuel power stations in the UK using carbon capture.

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P1.18- Nuclear Power

As well as fossil fuels, nuclear power can be used to generate electricity. Inside a nuclear reactor, atoms of uranium or plutonium undergo nuclear fission, which releases a huge amount of heat energy. The heat is used to turn water into steam, and from there on the process is the same as in a fossil fuel power station. However, because there is no combustion, no carbon dioxide is reduced. Nuclear power is very controversial.

• Huge amounts of evergy produced per kg of fuel
• No carbon dioxide produced- no cotribution to global warming
• Readily available fuel that won't run out for years

• Highly radioactive waste has to be buried deep underground
• Cost of taking the plant down when finished with (decommissioning) is very high
• Very slow start up time- does not meet change in demand easily
• Constant risk of radioactive waste being released into environment
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B1.19- Biomass and Biofuels

Biomass is a renewable energy resource. All forms of biomass involve material produced by living organisms. When used for burning, biomass is called biofuel, eg wood and woodchips from trees; alcohol fuels (eg ethanol); methane gas; nutshells; vegetable oils to make biodieselBiomass is the most common form of renewable energy.

• Uses other products which would normally be wasted- low fuel costs
• Carbon neutral
• Gives a hot water supply

• Releases atmospheric pollutants
• Ethical issues of using food land for growing fuel in devloping countries
• Power plants give visual pollution

Although biomass is burnt, releasing carbon dioxide, the amount of carbon dioxide the plant takes in whilst alive is almost equal to that released, making biofuels carbon neutral.

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P1.20- Solar and Wind Power

Solar panels- transfer light energy into electrical energy by knocking electrons out of the solar cell, so they can flow as a direct current

Advantages: require little maintenance, no need for fuel, no power cables so can be used in remote locations, do not produce any waste, renewable energy resource

Disadvantages: large area required to to generate as much energy as a thermal power station, less electricity on cloudy days and at night

Solar towers- mirrors reflect light into a spot at the top of the tower, can reach 500 degrees, then heats water into steam and follos process of thermal power station

Wind turbines- uses wind to drive the turbines directly, which turn a generator

Advantages: renewable, do not produce any waste, can be used in remote locations

Disadvantages: spoil the landscape, noise pollution, depend on the wind blowing, must be built in open areas, take up a lot of space to generate energy equivalent to a thermal power station

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P1.21- Energy from Water

Tidal barrages- when the tide is high, the water is held back by a barrage across a river estuary. After several hours the sea level on the other side has fallen. The water held back is now released, flowing through a set of turbines as it does so.

Advantages: renewable energy resource. Disadvantages: not many places where they can be used, generate power for 6-8 hours a day, high tide is not at the same time every day

Tidal stream turbine- turbines placed underwater where tidal streams are very strong. Advantages: renewable, generates electricity for 18-20 hours a day

Air tubes- the kinetic energy from waves can be used to drive air up and down a tube, which drives a turbine

Hydroelectric power- a dam is built into a hilly area to store water in a reservoir. Water flows downhill in pipes, passing tubines as it does so and generating electricity

Advantages: renewable energy resource, no need for fuel, start and stop very quickly. Disadvantages: reservoir must be built, which changes environment

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P1.22- The National Grid

Electricity is transferred around the country by the National Grid.

Power station (25kV)   Step-up transformer (400kV)   Power cables   Step-down transformer (132kV, or 25kV for trains)   Step-down transformer   Large industrial consumers (33kV) / small industrial consumers (11kV   step-down transformer) / homes, shops, workplaces (11kV   step-down transformer   240V)

The electricity goes from the power station to a step-up transformer, which increases the voltage. This allows it to be transported faster, but it is unsafe for them to be transferred into homes at that voltage, so it goes through a step-down transformer before entering the mains supply.

In power cables, more enrgy will dissipate to the surroundings with a higher current because of the heating effect that current has. The lower the current, the more energy is transferred to the end destination.

Some power cables are buried underground because they create visual pollution and to avoid tangling with objects, but they have to be waterproofed and insulated, and dug up if they require maintenance, which is all very expensive.

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P1.23- Matching Supply and Demand

The demand for electricity can go up and down depending on the time of year, day or what is being shown on TV. A sudden increase in the demand for electricity (eg half time at a football match) is called a pickup.

It is wasteful to constantly generate electricity at a high level, so power stations stop generating electricity at points of low demand, and start again when the demand increases. This is why it is important for a power station to have a fast start up time. Nuclear power stations have the longest start up time, followed by coal, natural gas and hydroelectric power with the fastest. Power engineers look at TV schedules and weather forecasts to predict when the most and least electricity will be required.

Because it can take hours to stop and start fossil fuel power stations, they are often left runing and a pumped storage system is used. When there is a low demand, water is pumped from a lower reservoir to a higher one in underground pipes using the unneeded energy that has been generated. When the demand increases, the water is allowed to flow back down to the lower reservoir, passing through turbines as it goes and re-generating energy.

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P1.24- Waves All Around Us

Waves are a series of oscillations or vibrations which travel from one place to another. All waves transfer energy from one place to another. They also all have some key features:

amplitude in metres (m)- maximum height of a wave as measured from the middle

wavelength in metres (m)- shortest distance between the same point on one wave and the next

frequency in hertz (Hz)- the number of waves passing a point per second (1 Hz = 1 wave/second)

The speed of a wave depends on its frequency and wavelength. The following equation can be used to calculate wave speed:

wave speed = frequency x wavelength

It can be rearranged to

frequency = wave speed / wavelength or wavelength = wave speed / frequency

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P1.25- Transverse and Longitudinal Waves

There are two types of wave: tranverse and longitudinal. Both transfer energy from one place to another, but their oscillations are different.

Transverse waves (think up and down on a slinky)

• Have peaks and troughs
• Oscillations are perpendicular to energy transfer
• Examples: water, light, microwaves, x-rays

Longitudinal waves (think forwards and backwards on a slinky)

• Oscillations are parallel to direction of energy transfer
• Made up of compressions and rarefractions
• Examples: one type of seismic waves, sound

In a speaker you can see the cone moving in and out. When it moves out, it creates a compression, causing the air to bunch up. When it moves back in, it creates a rarefraction, because the air is more spread out. This is how a longitudinal wave is made.

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P1.26- Experiments with Waves

Reflection

Light waves give a reflection like the one in a mirror, but sound waves can also reflect in the form of an echo. The law of reflection states that the angle of incidence is always equal to the angle of reflection, regardless of how rough the reflecting surface is. A normal line always has to be drawn when drawing out a ray diagram for reflection. This goes at 90 degrees to the surface.

Refraction

The material that a wave travels through is called the medium, eg air for sound and light waves. When a wave goes from one medium to another, it may be refracted. Refraction is when the speed of a wave increases or decreases upon entering a new medium. If a wave slows down then it bends towards the normal, and vice versa.

Diffraction

Waves spread out when they pass through a gap or move around an object. This spreading out is called diffraction. The longer the wavelength, the greater the diffraction. Diffraction is greatest when the wavelength is equal to the size of the gap.

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P1.27- Electromagnetic Waves

Electromagnetic waves are a type of transverse wave that does not require a medium to travel through. It is because of electromagnetic waves that light and infrared radiation from the sun can reach earth. All the waves in the electromagnetic spectrum travel at the same speed, but varying frequencies, energies and wavelengths.

Wave                          Wavelength                 Frequency/Energy           Use

Microwave                                                                                             Cooking, mobiles

Visible light                                                                                            Seeing

Ultraviolet light                                                                                       Tanning

X-ray                                                                                                      Medical (bones)

Gamma                       Lowest                            Highest                          Killing cancer cells

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P1.28- Communications and Optics

The fast speed of electromagnetic waves is very useful for communication. The first four waves in the electromagnetic spectrum are most commnonly used:

• Microwaves- mobile phones, satellite TV
• Infrared- remote controls, some internet connections
• Light- photography, some internet connections

They work by encoding information into the wave, which is then sent from the transmitter to the receiver. When the wave is received, the information is extracted. In general, shorter wavelengths can hold a greater amount of information per second,

Images formed by visible light in a mirror are virtual (not really there, but appear to be because the brain assumes light always travels in a straight line), upright (same way up as the actual object) and laterally inverted (flipped horizontally).

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P1.29- Sound Waves

Sound waves are created by the vibration of an object (eg voice is produced by the vibration of vocal chords). When these vibrations reach the ear, the brain interprets them as sound.

Sound waves can't travel through a vacuum because there are no particles to vibrate, but they can travel through all solids, liquids and gases. The denser the medium it is moving through, the faster the sound travels.

Pitch- the higher the frequency of a sound wave, the higher the higher the pitch (and vice versa)

Volume- the larger the amplitude of a sound wave, the louder the volume

A piece of equipment called an oscilloscope produces an image of a sound wave so that it is easier to see changes in pitch (frequency) and volume (amplitude).

Humans are able to hear sounds up to 20,000Hz. Anything above this frequency is called ultrasound. Some animals (for example, dogs) can hear much higher frequencies than humans can

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P1.30- The Doppler Effect

Anything that emits waves is called a wave source. A good example of a wave source is a race car, which produces a high pitched sound as it is going round the race course. The driver of the car hears a constant pitch because they are not moving away from the wave source and so the frequncy remains the same; however, a spectator will hear a change in pitch as the car first comes towards them and then moves further away.

This is because when the car is moving towards them, the sound waves are becoming bunched up, giving them a shorter wavelength. There are more waves reaching the person watching per second, and so the pitch is higher. When the car moves away from the observer, the sound waves it is emitting spread out more. Fewer waves reach the person each second, and the frequency and pitch decrease

The doppler effect occurs with light waves as well, but it is harder to demonstrate. It can also occur when the observer moves to or form the wave source, but as they have to be moving very fast to notice the doppler effect in this way, it is not a very common occurence. The doppler effect is used to measure the speed of passing vehicles by the police.

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P1.31- Red-Shift

The doppler effect occurs not only with sound waves but all waves.

When a light source moves away from a person, the light gets stretched. The wavelength increases. The light is shifted towards the end of the visible light spectrum with the largest wavelength, which is the end where the colour red is found (hence the name red-shift). When the light source moves towards someone, the opposite will occur. This is known as bue-shift.

This observation is not possible to see in every day life because light travels too fast.

Galaxies and red-shift

When we observe other galaxies in the universe, they are nearly always red-shifted. This must mean that they are moving away from us, and the light waves comng from them have increasing wavelengths as they get further away. We can also see that the furthest away galaxies have the greatest red-shift, meaning they must be moving the fastest. This has led us to the conclusion that the further away from us a galaxy is, the faster it is moving.

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P1.32- The Big Bang Theory

Evidence for the Big Bang Theory

• Red-shift

We have observed that galaxies furthest away from us must be moving the fastest because they have the greatest red-shift. This evidence suggests that the universe is expanding outwards, which also means it must have all began at one singular point for everything to be moving away from. An analogy to compare this to is a firework, which has thousands of tiny sparks all exploding from one central point. If you were to record a firework and re-wind it, you would see the sparks all starting from one point. This is the principle for the beginning of the universe.

• Cosmic Microwave Background Radiation (CMBR)

In the 1960s two scientists noticed that a form of microwave radiation was interfering with results from their experiment, no matter where they positioned their equipment. They came to the conclusion that this background radiation (later dubbed cosmic microwave background radiation), was heat left over from the Big Bang. As the universe cooled and expanded, the radiation was stretched out. It is now present everywhere. The Big Bang Theory is the only one to explain the presence of CMBR in our universe.

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P1 Part 2 Catch Up

• Some power stations use fossil fuels, biomass and nuclear fuels to heat water.
• Water in hydroelectric generators and geothermal areas drives the turbines directly. Solar cells convert the sun's radiation energy directly into electricity by knocking out electrons
• Different energy sources affect the environment differently (eg releasing substances into the atmosphere, producing noise and visual pollution, producing waste, destroying habitats)
• Electricity is distributed from power stations via the national grid.
• Increasing the voltage reduces the current required, thereby reducing energy lost by heat
• Waves transfer energy. They have frequencies, wavelengths and amplitudes. They can be reflected, refracted or diffracted
• Electromagnetic waves are transverse, sound waves are longitudinal
• Electromagnetic waves form a continuous spectrum. All travel at the same speed
• Radio waves, microwaves, infrared radiation and visible light are all used for communication
• Longitudinal waves show areas of compression and rarefraction
• The normal line is perpenicular to the reflecting surface. The angle of incidence is equal to the angle of reflection
• The Doppler Effect explains a change in wavelength and frequency of a wave as seen by an observer and, with CMBR, helps to prove the Big Bang Theory
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