Energy Resources and Energy Transfer Contents n

Energy Resources and Energy Transfer

Contents n n n Thermal Energy Transfer Efficiency Energy Resources Work, Power and Energy Electromagnetic Forces Electromagnetic Induction

Heat Transfer Heat is transferred in order to equalise the temperatures of the object and its environment A cup of coffee will cool down because it is giving out heat energy into the surroundings This drink (taken out of the fridge) will warm up because it is taking in heat energy from the surroundings

Conduction Atoms in a substance are always vibrating. If the substance gets hotter, the atoms vibrate more. The heat energy is given to the atoms, which makes them move about faster n Every time they collide with another atom, the heat energy is transferred n This is how heat travels through a solid n

Convection n n Hot air rises in cold air. Hot water rises in cold water This is called convection When hot air rises, colder air has to move in to replace it Convection cannot happen in solids, as the atoms aren't able to move around

Radiation n Hot objects radiate heat to their colder surroundings n Black and dull surfaces emit and absorb radiation well n White and shiny surfaces do not emit radiation well and reflect radiation instead of absorbing it

Insulation Air can convect the heat energy away from a house if it is able to move. If the air is trapped in small spaces it can't move so it doesn't convect the heat energy n Fibreglass keeps the air still n Trapped air insulates heat by not allowing it to escape n n Double glazing works in this way

Power Which boils quicker? Kettle with high power rating or Kettle with low power rating Power = how quickly the energy is transferred (from electrical to heat energy) High power = Kettle heats up quickly Low power = Kettle heats up slowly

Power The power rating of a light bulb. . . Power = how much energy is given to an appliance per unit of time Power (Watts) = voltage x current P V I

Cost of Electricity 1 unit = 1 k. Wh Number of units = power rating x time used

Efficiency n Power = energy transfer per second E P T Power = energy transferred/time taken (W) (J) (sec) During a movement or change of state (etc. ) energy is usually lost as heat energy to the surroundings n The energy inputted is therefore always higher than the useful energy taken out n Efficiency = (useful energy out/energy in) x 100 = %

Non-Renewable Fuels n All power stations generate electricity: - Fuel is used to produce heat energy - The heat energy heats water and turns it into steam - The steam is pushed at high pressure along pipes to the turbines - The steam makes the turbines spin, turning a generator which then produces electricity - The electricity is then supplied to houses, factories and schools via the national grid n Non-renewable (fossil) fuels are oil, gas and coal

Nuclear Fuels n n n Uranium is the fuel used in many nuclear power stations Uranium is not burnt like coal or gas but undergoes nuclear fission Atoms of uranium are split up which releases large amounts of energy Nuclear fission produces harmful radiation so people are sceptical Waste from these reactions is also radioactive Accidents are serious but very rare

Electromagnetic Forces A current (I) has a magnetic field (B) around it n A wire has a circular magnetic field around it n n If the current changes direction, so does the field

Electromagnetic Forces Magnets attract magnetic materials using a magnetic field n The magnetic field surrounds the magnet, and gets weaker as the distance from the magnet increases n Magnets should be called permanent magnets the magnetism is always there n Electricity makes a magnet much stronger n This can be turned on and off n

Electromagnetic Forces Magnets pick up paper clips etc. strong weak Electromagnets pick up cars etc.

Electromagnetic Forces n The magnetic field around a coil electromagnet can be increased by: - Increasing the current flowing through the wire - Adding loops on the coil (loops are long lengths of wire) - Placing an iron or steel core inside the coil Basic electromagnet

Electromagnetic Forces The Motor Effect: - When two magnets are placed close to each other, they the fields affect each other produce a force n If a wire carrying a current is placed inside this magnetic field, a force is produced. This is called the motor effect n The direction of the force will depend on the direction of the magnetic field and the direction of the current in the field n

Electromagnetic Forces n Fleming’s Left Hand Rule: - When creating a force, use Fleming’s LH Rule to determine in which way the motor will spin -

Electromagnetic Forces n We can increase the force produced by: - increasing the current - increasing the number of coils - increasing the magnetic field strength (stronger magnet)

Electromagnetic Induction • When a magnet is moved into a coil, an electrical current is induced • When the magnet stops, the induced current stops • When the magnet reverses, the electrical current reverses

Electromagnetic Induction Increase the voltage? … 3 ways… 1. Stronger magnet 2. Speed of magnet 3. Number of coils

Transformers

Transformers 4 coils produce 10 V 8 coils produce 20 V

Transformers Power stations step-up the voltage to reduce energy losses (but v high voltage) Pylons to houses step-down the voltage to reduce risk of electrocution

Summary n n n Thermal energy is transferred by conduction, convection and radiation Efficiency % = (useful output/total input) x 100 Fossil fuels are widely used energy resources but these are non-renewable E = Px. T, P = V x I, units = power (k. W) x time (hr) u Electromagnetic forces are used to create movement Movement is used to create voltage using electromagnetic induction