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Physics AQA P1
Infrared Radiation a) All objects emit and absorb infrared radiation. b) The hotter an object is the more infrared radiation it radiates in a given time. c) Dark, matt surfaces are good absorbers and good emitters of infrared radiation. d) Light, shiny surfaces are poor absorbers and poor emitters of infrared radiation. e) Light, shiny surfaces are good reflectors of infrared radiation. Infrared radiation can be detected. Uses?
Emitting Infrared Radiation worst emitter best emitter silver matt black white All objects emit (give out) some thermal radiation. Certain surfaces are better at emitting thermal radiation than others. Matt black surfaces are the best emitters of radiation. Shiny surfaces are the worst emitters of radiation. Which type of kettle would cool down faster: a black kettle or a shiny metallic kettle?
Absorbing Infrared Radiation worst emitter best emitter silver matt black white worst absorber best absorber Infrared waves heat objects that absorb(take in) them. Matt black surfaces are the best absorbers of radiation. Shiny surfaces are the worst emitters because they reflect most of the radiation away. Why are solar panels that are used for heating water covered in a black outer layer?
Application Questions Why are marathon runners wrapped in foil after a race? Why would dressing like these ninjas be a bad idea on a sunny day? Which t shirt would dry quickest on washing line? Why?
Kinetic Theory a) The use of kinetic theory to explain the different states of matter. b) The particles of solids, liquids and gases have different amounts of energy.
Kinetic Theory As you heat a substance, the heat energy is transferred to the particles in the substance as kinetic energy. This causes the particles to move further apart, decreasing the density of the substance.
Kinetic Theory A loss of heat energy will cause the opposite effect.
Application Questions Hot air balloons rise because a fuel is burned releasing heat. Using the kinetic theory, explain why the balloon rises. 2. (a) When carbon dioxide is turned from a gas to a solid, what two phases happen? (b)Does this require an input of thermal energy, or a removal of thermal energy?
Energy Transfer by Heating • a) The transfer of energy by conduction, convection, evaporation and condensation involves particles, and how this transfer takes place. • b) The factors that affect the rate of evaporation and condensation. • c) The rate at which an object transfers energy by heating depends on: • surface area and volume • the material from which the object is made • the nature of the surface with which the object is in contact. • d) The bigger the temperature difference between an object and its surroundings, the faster the rate at which energy is transferred by heating.
Energy Transfer by Heating gas solid liquid Particles that are very close together can transfer heat energy as they vibrate. This type of heat transfer is called conduction. Conduction is the method of heat transfer in solids but not liquids and gases.
Energy Transfer by Heating Warmer regions of a fluid are more densethan cooler regions of the same fluid. The warmer regions will risebecause they are more dense. The cooler regions will sinkas they are less dense. This is how heat transfer takes place in fluids and is called convection. The steady flow between the warm and cool sections of a fluid, such as air or water, is called a convection current.
Energy Transfer by Heating The Earth is warmed by heat energy from the Sun. How does this heat energy travel from the Sun to the Earth? infrared waves There are no particles between the Sun and the Earth, so the heat cannot travel by conduction or by convection. The heat travels to Earth by infrared waves. These are similar to light waves and are able to travel through empty space.
Energy Transfer by Heating 3. The walls have silvery surfaces, which prevent heat leaving or entering by radiation. How is a vacuum flask able to keep hot drinks hot and cold drinks cold? 2. The plastic (or cork) lid is an insulator and the screw top prevents convection currents escaping from the flask. 1. There is a vacuum between two layers of glass or steel, which prevents heat leaving or entering by conduction.
Energy Transfer by Heating Heat loss through evaporation.
Heating and Insulating Buildings a) U-values measure how effective a material is as an insulator. b) The lower the U-value, the better the material is as an insulator. c) Solar panels may contain water that is heated by radiation from the Sun. This water may then be used to heat buildings or provide domestic hot water. d) The specific heat capacity of a substance is the amount of energy required to change the temperature of one kilogram of the substance by one degree Celsius. Energy transferred = mass x specific heat capacity x temperature change
Heating and Insulating Buildings A thermogram shows the distribution of heat over the surface of a house. It highlights where heat is being lost. The white, yellow and red areas are the warmest, so these are the worst insulated parts of the house. The blue and green areas are the coolest, so these are the best insulated parts of the house.
Heating and Insulating Buildings specific heat capacity temperature change energy = mass x x The specific heat capacityof a material is the amount of energy required to raise 1kg of the material by 1°C. It can be used to work out how much energy is needed to raise the temperature of a material by a certain amount: Energy is measured in joules (J). Mass is measured in kilograms (kg). Temperature change is measured in °C. Specific heat capacity is measured in J/kg°C.
Heating and Insulating Buildings specific heat capacity temperature change energy = mass x x Using the specific heat capacity of water (4200 J/kg°C), how much energy is needed to increase the temperature of 600 g of water by 80°C in a kettle? Note: mass = 600 g = 0.6 kg energy = 0.6 x 4200 x 80 = 201 600 J
Energy Transfers and Efficiency a) Energy can be transferred usefully, stored, or dissipated, but cannot be created or destroyed. b) When energy is transferred only part of it may be usefully transferred, the rest is ‘wasted’. c) Wasted energy is eventually transferred to the surroundings, which become warmer. The wasted energy becomes increasingly spread out and so becomes less useful. d) To calculate the efficiency of a device using: Useful Energy Output Efficiency = X 100 Total Energy Input
Energy Transfers and Efficiency useful output energy total input energy energy efficiency = The energy efficiency of a device can be calculated using this formula: • Useful energy is measured in joules (J). • Total energy is measured in joules (J). • Energy efficiency does not have any units. • It is a number between 0 and 1 which can be converted into a percentage by multiplying by 100.
Energy Transfers and Efficiency All the energy transfers (useful and wasted) that are associated with a device can be represented by a Sankey diagram. Filament light bulb 100J electrical energy (input) 10J light energy (output) A Sankey diagram uses arrows to represent all the output energies. 90J heat energy (wasted) The thickness of each arrow is proportional to the amount of energy involved at that stage. Energy efficient light bulb 20J electrical energy (input) 10J light energy (output) 10J heat energy (wasted)
Transferring Electrical Energy a) Examples of energy transfers that everyday electrical appliances are designed to bring about. b) The amount of energy an appliance transfers depends on how long the appliance is switched on and its power. c) To calculate the amount of energy transferred from the mains using: Energy transferred = power x time d) To calculate the cost of mains electricity given the cost per kilowatt-hour.
Transferring Electrical Energy electrical energy = power x time 1 unit of electricity = 1 unit of electrical energy The amount of electrical energy (i.e. the amount of electricity) used by an appliance depends on its power and how long the electricity is used for. Power is measured in kilowatts (kW) and the time is measured in hours (h), so what are the units of electricity measured in? = 1 kilowatt hour (kWh) Example: How many units of electricity is 17.6 kWh? 17.6 units
Transferring Electrical Energy Electricity costs money, which is why every home has an electricity meter. The meter records how much electricity is used in a house in units of electrical energy. The units of electrical energy are called kilowatt hours (kWh). The cost of an electricity bill is calculated from the number of units used.
Transferring Electrical Energy cost = number of units x cost per unit The cost of electricity is the number of units of electrical energy multiplied by the cost per unit. Example: How much would 10 units of electricity cost at a price of 9p per unit? cost = 10units x 9p/unit = 90p
Transferring Electrical Energy A kettle uses 45.2 kWh of energy.If electricity costs 10 p per unit, how much does it cost to use the kettle? Number of units: number of units of electricity = number of kilowatt hours =45.2 units Cost of electricity: cost = number of units x cost per unit = 45.2 units x 10 p / unit = 452 p or £4.52
a) 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 sources include: the fossil fuels (coal, oil and gas) which are burned to heat water or air uranium and plutonium, when energy from nuclear fission is used to heat water biofuels that can be burned to heat water. b) Water and wind can be used to drive turbines directly. c) Electricity can be produced directly from the Sun’s radiation. d) In some volcanic areas hot water and steam rise to the surface. The steam can be tapped and used to drive turbines. This is known as geothermal energy. e) Small-scale production of electricity may be useful in some areas and for some uses, e.g. hydroelectricity in remote areas and solar cells for roadside signs. f) Using different energy resources has different effects on the environment. These effects include: the release of substances into the atmosphere, the production of waste materials, noise and visual pollution, the destruction of wildlife habitats. • Generating Electricity
Energy resources can be classified into two groups. Renewable Non-renewable • Generating Electricity Renewable energy resources can be replaced or regenerated and will never run out (at least not for a very long time). Non-renewable energy resources will eventually run out – once used they cannot be used again. Examples: wind and solar. Examples: coal and oil.
The National Grid a) Electricity is distributed from power stations to consumers along the National Grid. b) For a given power increasing the voltage reduces the current required and this reduces the energy losses in the cables. c) The uses of step-up and step-down transformers in the National Grid.
The National Grid Step up transformer Step down transformer Homes Power station • The voltage is altered in The NationalGrid with the use of step-up and step-down transformers. • The voltage is ‘stepped up’ when it leaves the power station to reduce the current - this reduces the amount of energy loss • The voltage is then ‘stepped down’ before it reaches our homes
a) Waves transfer energy. b) Waves may be either transverse or longitudinal. c) Electromagnetic waves are transverse, sound waves are longitudinal and mechanical waves may be either transverse or longitudinal. d) All types of electromagnetic waves travel at the same speed through a vacuum (space). e) Electromagnetic waves form a continuous spectrum. f) Longitudinal waves show areas of compression and rarefaction. g) Waves can be reflected, refracted and diffracted. h) Waves undergo a change of direction when they are refracted at an interface. i) The terms frequency, wavelength and amplitude. j) All waves obey the wave equation: v = f x k) Radio waves, microwaves, infrared and visible light can be used for communication. • Waves
Vibrations Vibrations • Transverse Waves Wave Direction The vibrations are at 90O or right angles to the direction of the waves.
peak trough Certain parts of a transverse wave have special names. The high points of a transverse wave are called peaks and the low points of a transverse wave are called troughs. • Transverse Waves