Energy

P1a Energy Heat theory Convection (l & g) Condensation & evaporation (l&g) TheThe Rate of heat transfer Energy efficiency at home at Specific heat capacity.. Energy transfer (J) Efficiency of machines % % Sankey diagrams  Choosing electrical appliances electrical Cost of electricity £ Heat radiation Kinetic Theory Conduction solid

Heat Radiation Heat transfer Conduction Convection Radiation particles In Solids In liquids & gases Emit & absorb Emit from surface If hotter than surroundings... emit more than absorb. Hotter it is the more energy it will radiate. Surface colour and texture IR waves colour texture dark matt Good absorber Good emitter Good reflector light shiny Heat energy flows away from hotter to cooler surroundings

Kinetic Theory & conduction gas liquid Solid 3 states of matter Strong forces of attraction Fixed pattern Not much Energy - vibrate forces of attraction weaker than In a solid Particles can move past each other More energy than in a solid, move randomly at low speeds Irregular pattern forces of attraction VERY weak Particles have a lot of energy Move randomly at high speeds When you heat a substance you give it more KE. The particles vibrate more / move faster.. Melting + boiling Describes how particles behave because of the amount of KE that they have

Conduction in solids Have free electrons Vibrating particles pass on their extra KE to their neighbours by colliding with them Faster in dense solids Metals are good conductors Poor conductors insulators Have larger spaces between particles.

Conduction When you heat a metal strip at one end, the heat travels to the other end. As you heat the metal, the particles vibrate, these vibrations make the adjacent particles vibrate, and so on and so on, the vibrations are passed along the metal and so is the heat.

Convection Liquids & gases ONLY All about changes in density Hotter particles with more KE move from the hotter to the colder region TAKING THEIR ENERGY WITH THEM! Where the particles gain energy, they move faster and spread out. EXPANDS The gas / liquid in this area becomes less dense. The less dense gas/ liquid displaces the cooler, more dense gas/liquid. The more dense gas / liquid sinks nearer to the heat source......it gains energy This is now a convection current!

Water movement Hot water rises Cooler water sinks Convection current Cools at the surface

Where is the freezer compartment put in a fridge? Freezer compartment It is put at the top, because cool air sinks, so it cools the food on the way down. It is warmer at the bottom, so this warmer air rises and a convection current is set up.

Condensation & evaporation Evaporation Condensation Liquid  gas Gas  Liquid Loss of KE Gain KE Particles must be; travelling fast enough to escape the attractive forces between the particles. travelling in the right direction. The average KE of the particles left in the liquid is lower....so the liquid is cooler! Increasing the rate depends on; 1.Decreasing temperature of the gas...Less KE. 2.Decreasing temperature of the surface the gas touches. 3.Increasing the density of the gas...bigger force of attraction between particles. 4. Low airflow....increases the concentration of the gas. Increasing the rate depends on; 1.Increasing temperature of the gas...More KE. 2.Increasing the surface area. 3.decreasing the density of the gas...less force of attraction between particles. 4. High airflow....lowers the concentration of the gas in the air Useful to control body temperature.... Sweating!

Rate of heat transfer Depends on.... Surface area of an object Volume of an object IR radiation Radiators fins Heat sinks computers Smaller volume will cool more quickly. Type of material made from Insulator or conductor What is object in contact with? You need to be able to describe how devices limit heat transfer.....vacuum flask. You need to describe how animals (including humans control heat transfer.

Energy efficiency at home Effectiveness Cost - effectiveness Are NOT the same thing! Give you the most money every year Have the shortest payback time Payback time How long it takes for the money you have saved on the bills to equal the cost of putting in the insulation. Types of heat transfer Cavity wall insulation Loft insulation Draught proofing Hot water tank jacket Thick curtains convection conduction radiation U-value Shows how fast heat is transferred through a material The better the insulator the lower the U-value

Specific heat capacity Tells you how much energy materials can store It takes more heat energy to increase the temperature of some materials compared to others. These materials also release more energy as they cool.....they act as heat stores The amount of energy needed to raise the temperature of 1Kg of the substance by 1°C Energy = mass (m) x specific heat capacity (c) x temperature change (Ɵ) j Kg j/kg/°C °C E m x c x Ɵ

Energy transfer Chemical Elastic potential Gravitational potential GPE Thermal heat Nuclear Kinetic KE Sound Light Electrical Principle of conservation of energy Energy can be transferred usefully from one form to another or dissipated (spread out through surroundings). It can NEVER be created or destroyed All types of stored energy

Efficiency of machines The energy /power used to do the job you want the machine to do. Efficiency = Useful energy out Total energy in Efficiency = Useful power out Total power in Energy that is not transferred usefully from one form to another is dissipated (spread out through surroundings). Usually heats the surroundings Difficult to collect in or use Have to consider cost- effectiveness when choosing appliances Low energy bulb = 4x as efficient as an ordinary bulb, and last longer, but they cost more. LED bulbs are even more efficient as an ordinary bulb and last even longer, but they cost a lot more & don’t give out as much light. Heat exchanger

Sankey diagrams Total energy in wasted energy Useful energy Useful energy Thickness of the line represents the amount of energy. Can be drawn to scale so that the width of each arrow is proportional to the amount of energy.

Cost of electricity Unit of electricity Kilowatt-hours kWh E P x t Energy transferred = Power x time J W s Use kWh because we are dealing with huge amounts of electrical energy (joules). Number of units / electrical energy transferred (kWh) = Power (kW) x Time (hours) Cost = number of units x cost of 1 unit You must always check the units first! You must be able to read an electricity meter

Compare practical advantages Compare cost- effectiveness Compare efficiency Compare energy consumption Choosing electrical appliances Limited electrical supplies? Cost of batteries clockwork Environmental cost You may be given data to help you compare.....always quote the amounts in your answers! Standard of living is affected by access to electricity convenience safety Fridges (food & vacines) Public health (Hospitals) Life expectancy communication