Energy Transfer by Heating - 1
1.1 - 1.5
- Dark, matt surfaces are good absorbers but bad reflectors of IR.
- Shiny, light surfaces are good emitters but bad absorbers of IR.
- Solid: particles vibrate about a fixed position-fixed shape.
- Liquid: particles are in contact with each other but move randomly, so can flow.
- Gas: particles are far apart and move randomly and fastly, so has no fixed shape and can flow.
- Conduction- mainly in solids: particles at one end of the solid gain kinetic energy which is trasferred to neighbouring particles, transferring energy through the solid. Metals are good conductors because they have free electrons which gain energy when heated, moving along the metal and transferring energy by colliding with other particles.
- Poor conductors are called insulators, like woll because it contains trapped air.
- Convection-mainly in fluids (liquids & gases): When a fluid is heated it expands , becoming less dense and rising, replacing cool, denser fluid with warm fluid, causing convectional currents, transferring energy throughout the fluid. It can be done small scale, like heating water in a beaker, or large scale, like heating the air above land and sea-convetional currents is responsible for wind.
- Evaporation: takes place when the most energetic liquid molecules escape from the liquid's surface, entering the air. The average kinetic energy of the remaining molecules is less of the temperature of the liquid decreases. Evaporation causes cooling, and is increased by: -increasing surface area of the liquid. - increasing temperature of the liquid. -having a draught of air across the liquid surface.
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Energy Transfer by Heating - 2
1.6 - 1.9
- Condensation: This often takes place on places like windows and mirrors, and is increased by: -increasing surface area. -Reducing surface temperature.
- The bigger the temperature between two substances, the higher the rate of energy transfer.
- Rate of energy transfer is also affected by materials an object is in contact with, an object's shaoe and an object's surface area.
- To max the rate of energy transfer; good conductors, black paint & having air flow maxed can be used.
- To minimise, good insulators, white and shiny objects and prevention of convectional currents is used.
- Vacuum flask:-Inside surfaces silvered to stop radiation.-A vacuum preventing conduction & convection.
- Specific heat capacity: E=MC(theta): E= energy transferred, in joules. M= mass, in kg. C= specific heat capacity; J/KgdegreesC. ɵ=temperature change, degrees C.
- Different substances have different SHCs, even if they have the same mass.
- U-Values: energy/s passing per metre squared for 1 degree celsius temperature difference. The lower it is, the better it can be used as an insulator.
- Solar heating panels: contain water heated by radiation from the Sun, which can be used to heat buildings or provide hot water. They don't use fuel, but are expensive to buy and don't work at night.
- To reduce fuel bills in houses, you can install fibreglass loft insulation , have cavity wall insulation, install double/triple glazed windows, have draught excluders & put aluminium foil behind radiators.
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2.1 - 2.4
- Energy can exist as: -Active energies: Kinetic, sound, heat, light.
-Stored energies: Gravitational potential, Elastic, electrical, chemical.
- Energy can be transformed from one form to another-anything above ground has gravitational potential energy. A falling object transfers that to kinetic energy.
- It is impossible to creat/destroy energy-it is only transferred. In a solar cell, light energy is transferred to electrical energy.
- A machine: something transferring energy from one place to another or from on form to another.
- You have useful and wasted energy. No machine, apart from an electrical heater, is 100% efficient. Both useful & wasted energy is eventually transferred to surrounding, making them warm up but eventually it is hard to use for further energy transfers. A hairdryer uses energy for heat and kinetic, but wastes as sound.
- Energy~measured in joles, form all forms of energy.
- Efficiency=useful energy transferred ÷ total energy supplied (×100%).
- A Sankey diagram can be used to represent energy transfer in an appliance.
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3.1 - 3.4
- Common appliances can include lamps, to produce light and electric mixers, to produce kinetic energy.
- Many transfer energy by heating, which is a useful energy in a hairdryer, but energy is often wasted.
- The power of an appliance is the rate of energy transfer, using watt, with the symbol 'W'. An appliance with 1 watt tranfers 1 joule of electrical energy per second. Most power units are given in kW-kilowatts.
- Power is given by: P=E÷t. P~ power in watts, W. E~ energy, in joules, J. t~time in seconds, s.
- The efficiency equation can be written with power: Efficiency=useful power out÷total power (×100%)
- Companies that supply mains electricity charge for the amount used, measured in kWh (amount of energy transferred by a 1 kW appliance when used for 1 hour."
- To work out how many kWh: E=P×t. E~energy transfer in kWh. P~power, kW. t~time, in hours.
- To find the electrical bill, the number of kWh is multiplied by cost per kWh, which is set by the company: total cost= number kWh × cost per kWH.
- To compare cost effectiveness, you should consider: the cost of buying the appliance, the cost of installation, running costs, maintenance costs, environmental costs, interest charged on a loan to buy it.
- Most want to reduce energy bills, so buy newer, more efficient appliances like a new fridge, and intall materials to reduce energy wastage like double glazing on windows.
- Payback time=cost÷amount saved each year.
- Energy loss in a house: 25%-roof, 15%-floor, 35%-walls, 15%-draughts and 10%-windows.
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Generating electricity- 1
4.1 - 4.4
- Power stations: steam is made to drive a turbine, which is coupled to a generator to produce electricity.
- The energy used to heat water to turn it into steam can be made from burning fossil fuels: coal, oil & gas.
- Coal-Pros: Reliable & more reserves than other fossil fuels. Cons: Non-renewable, CO2&SO2 produced.
- Oil-Pros: Reliable. Cons: Non-renewable, CO2 & SO2 produced.
- Gas-Pros: Reliable. Cons: Non-renewable, CO2 produced.
- Nuclear power- uranium and sometimes plutonium is used which produces lots of energy from nuclear fissions, when the nucleus of the atoms are split in two, which is used to heat the water.
Pros: No polluting gases & reliable. Cons: Non-renewable, produces hazardous nuclear waste hard to dipose & risk of nuclear accident.
- Wind- wind directly turns a turbine on a tower, to generate electricity.
Pros: Renewable, no produce of polluting gases, free energy resource. Cons: Requires many large turbines, unreliable.
- Wave- waves are used to make a floating generator move up and down, turning the generator so it generates electricity. Pros: Renewable, no production of polluting gases, free energy resource. Cons: can be a hazard to boats, unreliable.
- Hydroelectric-Rainwater is collected and flows downhill, which drives turbines at the end of the hill.
Pros: Renewable, no production of polluting gases, reliable in wet areas, free energy resource. Cons: Only works in wet/hilly places, damming the areas causes flooding and damages local ecology.
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Generating electricity- 2
4.4 - 4.6
- Tidal- water from high tides are trapped behind a barrage, then are released and drive a generator.
Pros: Renewable, no production of polluting gases, reliable-tides twice a day, free energy resource.
Cons: Only few river estuaries are suitable. -Building a barrage affects local ecology.
- Geothermal- Small scale- heating water by flowing it underground and pumping it back up for hot water and heating. Large scale- flowing water really deeply below ground to volcanic areas which turn it to steam to drive a turbine.
Pros: Renewable, no production of polluting gases, free energy resource. Cons: Only economically viable in few places, and drilling through large depth of rock-hard and expensive.
- Solar- Pros: Renewable, no production of polluting gases, reliable in daytime in hot places, free energy resource. Cons: Solar cells only produce a small amount of electricity, unreliable in less sunny places.
- National Grid- system of electricity distribution in Britain. At a power station, the voltage of the electricity is raised with step-up transformers to 132kV from 25kV, in order to lower the current, therefore saving more energy as it travels through cables. When it reaches step-down transformers, the voltage is reduced to 230V so it is safe to use at home.
- Demand for electricity changes during the day, but power stations provide a constant amount of electricity-base load amount. When demand is low, excess electricty is stored then used for when demand is higher.
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5.1 - 5.3
- Waves- tranfer energy. There are two types; longitudinal and transversal.
- Transversal: the oscillation/vibration of the wave is perpendicular to the direction of travel. All electromagnetic waves, waves with string, and secondary seismic waves are transversal.
- Longitudinal: The vibration/oscillation of the wave is parallel to the direction of travel. Sound waves, slinky waves, and primary seismic waves are examples. The vibrations are compressions and rarefactions.
- The amplitude is the measurement between the rest position on the wave to a peak. A complete wavelength is the distance from one crest to the next, or from one trough to the next. The frequency is the number of crests passing a point per second, given in hertz-Hz.
- The wave speed is given by: v=f×wl (you probably know the proper symbol for that). v=wave speed, in metres per second- m/s. f is the frequency in hertz, Hz. wl=wavelength in metres, m.
- The same term apply for a longitudinal wave- the distance from the middle of one compression to another, and the same for rarefactions.
- A virtual image is produced in a mirror due to reflection of light. There can be a normal line perpendicular to the mirror, and the angle from the normal line to the incident ray is 'i', and the angle from the normal line to the reflected ray is 'r'. 'i'='r'. A virtual image is the same distance behind the mirror as the real object is in front- rays of light of light only appear to pass through it. The image is upright and the same size as the object.
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5.4 - 5.7
- Refraction is the bending of a wave and when it changes speed entering a new medium. Waves change speed when entering a new medium. When they enter a denser medium, they slow down and bend towards the normal line, and when they enter a less dense medium, they speed up and bend away from the normal line.
- However, if the wave is travelling along the normal line, then there is no direction change.
- The angle between the normal line and the ray at first is the incident angle. The angle somewhat opposite it, where the wave changes direction enetering a new substance, is the angle of refraction.
- Diffusion is a property of all waves-it is the spreading of waves when they pass through a gap or around an obstacle. If the gap is wide, then there is less diffraction, but if the gap is narrower, then there is more diffraction.
- Sound is caused by mechanical vibrations, which then travel as a wave. It can travel through liquid, solids and gases. They travel fastest in solid and slowest in gases.
- However, they cannot travel through a vacuum-they need particles. This can be proved by the 'bell jar' test.
- For humans, the frequency range is from 20Hz to 20kHz. The ability to hear higher frequencies declines with age. Sound waves can be reflected, especially by hard, flat surfaces.
- The higher the pitch of a sound, the higher it sounds. The higher the amplitude, the louder it sounds. In an instrument, something is vibrated to create the sound.
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Electromagnetic Waves- 1
6.1 - 6.3
- All EMS waves can travel through space- a vacuum, at the same speed, but at different wavelengths and frequencies. They consist of: Radiowaves, Microwaves, Infrared Radiation, Visible Light, Ultraviolet, X-Rays, Gamma rays. The speed is 3 × 10^8m/s.
- Radio waves can have wavelengths over 10km, gamma rays can have wavelengths as short as 10^-15m.
- V=f×wavelength. V=wave speed; 3×10^8ms/s. F=frequency in hertz, Hz. Wavelength is in metres, m.
- Visible light is the only part of the EMS that our eyes can detect. Different wavelengths are seen as colours.
- Microwaves are used in communications- they can pass through the atmosphere so are used for mobile phone networks.
- Radiowaves transmit radio and TV programs and carry mobile phone signals.
- An alternating voltage aplied to an aerial emits radiowaves with the same frequency as the alternating voltage. When the waves are recieved they produce an alternating current in the aerial with the same frequency as the radiation recieved.
- Optical fibres-useful in communications because they carry useful information.
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Electromagnetic Waves- 2
6.4 - 6.5
- Red shift-the wavelength increasing when something is moving at a very fast speed. The frequency decreases and the wavelength increases.
- The more red shift, the further away and faster the galaxy is. Absorption lines from a galaxy are closer to the red end of the spectrum. Red shift provides evidence for the Big Bang theory.
- Big Bang Theory- the theory that space, matter and time all came from a single point 14 billion years, and the universe started expanding.
- Cosmic microwave background radiation-as the universe expands, the wavelength of waves in space created by the Big Bang did too. At the beginning they started off as gamma rays but the waves 'stretched' over billions of years to become microwaves.
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