AQA GCSE Physics - Unit 1

1. Energy Transfer by Heating
1. 1.1- Infrared radiation
  1. Infrared radiation is energy transfer by electromagnetic waves.
    1. All objects emit infrared radiation.
      1. The hotter an object is , the more infrared radiation it emits in a given time.
        Infrared radiation can travel through a vacuum because it doesn't involve particles, that's how we get heat from the sun.
2. 1.2- Surfaces and radiation
  1. Dark, matt surfaces emit infrared radiation more quicker than light, shiny surfaces so it will tranfer energy and cool down quicker.
    1. Dark, matt surfaces absorb infrared radiation more quickly than light, shiny surfaces so it will get hotter.
      1. Light, shiny surfaces reflect more infrared radiation than dark, matt surfaces.
3. 1.3- States of matter
  1. Flow, shape, density and volume are the properties used to describe each state of matter.
    1. The particles in a solid are held next to each other, vibrating in their fixed positions.
      1. The particles in a liquid move about at random and are in contact with each other ( they can flow).
        The partices in a gas move about randomly and are much farther apart than particles in a solid or liquid so it can flow. They also move faster and and gas is less dense than a solid or a liquid.
4. 1.4- Conduction
  1. Metals are the best conductors.
    1. Materials such as wood and fibreglass are good insulators because they contain trapped air.
      1. Conduction in a metal is mainly due to free electrons tranferring energy inside the metal when they gain kinetic energy.
        Non-metals are poor conductors because they do not contain free electrons.
        Conduction occurs mainly in solids because most liquids and gases are poor conductors. If one end of a solid is heated, the particles at that end gain kinetic energy and vibrate more. this energy is passed to neighbouring particles and in this way energy is transferred through the solid.
5. 1.5- Convection
  1. Convection is the circulation of a fluid (liquid or gas) caused by heating it.
    1. Convection takes place only in liquids and gases (fluids).
      1. Heating a liquid or a gas makes it less dense so it rises and causes circulation.
        When a fluid is heated, it expands causing it to become less dense and rise. The warm liquid is replaced by coller, denser fluid. The resulting convetion current transfers energy throughout the fluid.
6. 1.6- Evapouration and condensation
  1. Evapouration is when a liquid turns into a gas. Evapouration takes place because the most energetic liquid molecules escape from the liquids surface and enter the air. Therefore the average kinetic energy of the remaining molecules is less so the temperature of the liquid decreases.
    1. Condensation is when a gas turns into a liquid. This often takes place on cold surfaces such as windows and mirrors.
      1. The rate of evapouration is increased by: increasing the surface area of the liquid, increasing the temperature of the liquid and creating a draught of air across the liquid's surface.
        The rate of condensation is increased by: increasing the surface area and reducing the surface temperature.
7. 1.7- Energy transfer by design
  1. The rate of energy transfer to or from an object depends on: the shape, size and type of material of the object, the materials the object is in contact with and the temperature difference between the object and its surroundings.
    1. To maximise the rate of energy transfer and keep things cool, we might use things that are: good conductors, painted black and have the air flow around them maximised.
      1. To minimise the rate of energy transfer and keeps things warm, we might use things that are: good insulators, white and shiny and prevent currents by trapping air in small pockets.
8. 1.8- Specific heat capacity
  1. The greater the mass of an object, the more slowly its temperature increases when it's heated and the more energy required.
    1. The rate of temperature change in a substance when heated depends on the energy transferred to it, its mass and its specific heat capacity.
      1. Specific heat capacity is the amount of energy needed to heat 1 kilogram of a substance by 1 degree Celsius.
9. 1.9- Heating and insulating buildings
  1. The rate of energy transfer to and from our homes can be reduced.
    1. U-values tells us how much energy per second passes through different materials. The lower the U-value the better the material is as an insulator.
      1. Solar heating panels do not use fuel to heat water (they use radiation from the sun) and are cheap to run but they are expensive to buy and install.
2. Using Energy
1. 2.1- Forms of energy
  1. Energy exists in different forms.
    1. Energy can be transferred from one form into another form.
      1. When an object falls and gains speed, its gravitational potential energy decreases and its kinetic energy increases.
        Energy exists in different forms such as: light, sound, heat, kinetic, nuclear, electrical, gravitational potential, elastic potential and chemical.
2. 2.2- Conservation of energy
  1. Energy can be transferred from one form to another or from one place to another.
    1. Energy cannot be created or destroyed.
      1. Conservation of energy applies to all energy changes.
        Conservation of energy means the total amount of energy is always the same.
3. 2.3- Useful energy
  1. Useful energy is energy in the place we want it and the form we need it.
    1. Wasted energy is energy that is not useful energy.
      1. Useful energy and wasted energy both end up being transferred to the surroundings, which become warmer.
        As energy spreads out, it gets more and more difficult to use for further energy transfers.
        Energy is often wasted because of friction between the moving parts of a machine. This energy warms up the machine and its surroundings.
        Sometimes friction can be useful, for example in the brakes of a bicycle or a car. Some of the kinetic energy of the vehicle is transferred to energy heating the brakes.
4. 2.4- Energy and efficiency
  1. The efficiency of an appliance = useful energy transferred by the appliance divided by total energy supplied to the appliance x100%.
    1. No machine can be more than 100% efficient.
      1. Measures to make machines more efficient include reducing: friction, air resistance, electrical resistance and noise due to vibrations.
        The energy transfer through an appliance can be represented by a sankey diagram.
3. Electrical Energy
1. 3.1- Electrical appliances
  1. Electrical appliances can transfer electrical energy into useful energy at the flick of a switch.
    1. Uses of everyday electrical energy appliance include: heating, lighting, making objects move and creating sound and visual images.
      1. An electrical appliance is designed for a particular purpose and should waste as little energy as possible.
2. 3.2- Electrical power
  1. Power is rate of transfer of energy.
    1. Power = Energy divided by time taken (in seconds) for the energy to be transferred.
      1. An appliance with 1 Watt transfers 1 Joule of electrical energy to other forms of energy every second.
3. 3.3- Using electrical energy
  1. The kilowatt-hour is the energy supplied to a 1kW appliance in 1 hour.
    1. Energy transferred in kWh = Power of the appliance x the time taken for energy to be transferred.
      1. Total cost = number of kWh x cost per kWh.
4. 3.4- Cost effectiveness matters
  1. Cost effectiveness means getting the best value for money.
    1. To compare the cost effectiveness of different appliances, we need to take account of a number of different costs.
      1. The costs may include: the cost of buying the appliance, the cost of installing the appliance, the running costs, the maintenance costs, environmental costs and the interest charged on loan to buy the appliance.
        The payback time is the time it takes for an appliance or installation to pay for itself in terms of energy savings.
        Payback time (in years) = Cost of installation divided by savings per year
4. Generating electricity
1. 4.1- Fuel for electricity
  1. Electricity generators in power stations are driven by turbines.
    1. Coal, oil and natural gas are burned in fossil-fuel power stations.
      1. Uranium or Plutonium is used as the fuel in a nuclear power station.
        Biofuels are renewable sources of energy which can generate electricity.
        Most power stations burn fuels to produce energy to heat water. In a nuclear power station uranium is not burned; the energy comes from the process of nuclear fission.
        Nuclear power stations don't release greenhouse gases unlike fossil-fuel power stations but they do produce radioactive waste that must be stored safely for a long time.
2. 4.2- Energy from wind and water
  1. A wind turbine is an electricity generator on top of a tall tower.
    1. Waves generate electricity by turning a floating generator.
      1. Hydroelectricity generators are turned by water running downhill.
        A tidal power station traps each high tide and uses it to turn generators.
3. 4.3- Power from the Sun and the Earth
  1. Solar cells transfer solar energy directly into electricity.
    1. Solar heating panels use the Sun's energy to heat water directly.
      1. Geothermal energy is produced inside the Earth by radioactive processes and this heats the surrounding rock. In volcanic or other suitable areas, very deep holes are drilled and cold water is pumped down to the hot rocks. There it is heated and comes back to the surface as steam which is used to drive turbines that turn generators and so electricity is produced.
        Solar energy from the Sun travels through space to the Earth as electromagnetic radiation.
4. 4.4- Energy and the environment
  1. Burning fossil fuels produces greenhouse gases that cause global warming.
    1. Nuclear fuels produce radioactive waste.
      1. Using renewable energy resources can affect plant and animal life.
5. 4.5- The National Grid
  1. The National Grid distributes electricity from power stations to our homes.
    1. Step-up and step-down transformers are used in the National Grid.
      1. A high grid voltage reduces energy wastage and makes the system more efficient. Step-up transformers increase the voltage before it is transmitted across the grid.
        Step-down transformers decrease the voltage to 230V so it is safe to use in our homes.
6. 4.6- Big energy issues
  1. Gas-fired power stations and pumped-storage power stations can meet variations in demand.
    1. Nuclear, coal and oil power stations can meet base-load demands.
5. Waves
6. Electromagnetic Waves

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	Criado por Charlotte Stobbs mais de 9 anos atrás