Edexcel GCSE Physics: Electromagnetic Induction Notes PDF

Edexcel GCSE Physics Topic 13: Electromagnetic induction Notes (Content in bold Higher Tier only) This work by PMT Education is licensed under https://bit.ly/pmt-cc https://bit.ly/pmt-edu-cc CC BY-NC-ND 4.0...

Edexcel GCSE Physics Topic 13: Electromagnetic induction Notes (Content in bold Higher Tier only) This work by PMT Education is licensed under https://bit.ly/pmt-cc https://bit.ly/pmt-edu-cc CC BY-NC-ND 4.0 https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc Current Induction (Physics only) - Current is induced if a wire is moved in a magnetic field - The Conductor (wire) forms a potential difference (electrons move to one side of the conductor as the field changes) - If the conductor is connected in a circuit, a current will flow o (This current will produce its own magnetic field) o (The direction of this new field is in the opposite direction to the first field) ▪ (I.e. it opposes the original change) Production (Physics only) - Small-scale o Spinning a coil of wire in between two permanent magnets will cause a current to flow in the wire, which can be shown by a sensitive ammeter (only milliamps will be generated) o Passing a wire through a field will also show a deflection in an ammeter (a reading). - Large-scale o In a thermal power station, water heats up and evaporates to form steam ▪ Combustion of fossil fuels / nuclear fission may cause this o The steam is put under pressure and forced into a turbine o This causes the turbine to rotate, which is connected to a massive coil of wire in a strong magnetic field (the generator) o Current is generated in the coil by the spinning motion of the coil through the field. Factors that affect the size of the current/voltage produced: - Number of coils of wire - Speed of rotation - Magnetic field strength Alternator - Every half turn, the current switches direction, as the wire will be in the opposite orientation compared to its starting position (see figure). o Use the Left Hand Rule to show the direction of the current induced switches as it moves up or down - This produces AC. Dynamo - Same set up as an alternator. - At end of the coil, there is a ‘commutator’ o A metal ring that reverses the sign of the current that flows from the coil – ensuring current output remains positive o Every half-turn the commutator switches the sign of the current, so it remains positive - This produces DC. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc Microphones and Loudspeakers - Produce a current which is proportional to the sound signal - Fixed magnet is at the centre, and the coil of wire around the magnet is free to move - Pressure variations in the sound waves cause the coil to move, and as it moves current is induced in the coil (because it passes through the magnetic field) - This current is then sent to a loudspeaker - The Loudspeaker setup is identical - Current flows into the coil - The magnetic field from magnet and from current interact, causing the coil to move - The cone therefore moves - Producing pressure variations, making sound Transformers - AC in first coil creates a changing magnetic field - This changing magnetic field cuts through the secondary coil - This induces a current in the secondary coil o Which is also AC o If primary current was DC, magnetic field produced will be constant, not inducing anything in the secondary coil - (Physics only) More coils on secondary? Step up transformer, as voltage will be increased, as changing field will cut through more of the secondary wire inducing a larger pd - (Physics only) Fewer coils on secondary? Step down transformer, as smaller pd forms on secondary 𝒏𝒖𝒎𝒃𝒆𝒓 𝒐𝒇 𝒄𝒐𝒊𝒍𝒔 𝒐𝒏 𝒑𝒓𝒊𝒎𝒂𝒓𝒚 𝒑𝒅 𝒐𝒇 𝒑𝒓𝒊𝒎𝒂𝒓𝒚 = 𝒏𝒖𝒎𝒃𝒆𝒓 𝒐𝒇 𝒄𝒐𝒊𝒍𝒔 𝒐𝒏 𝒔𝒆𝒄𝒐𝒏𝒅𝒂𝒓𝒚 𝒑𝒅 𝒐𝒇 𝒔𝒆𝒄𝒐𝒏𝒅𝒂𝒓𝒚 𝑵𝒑𝒓𝒊𝒎𝒂𝒓𝒚 𝑽𝒑𝒓𝒊𝒎𝒂𝒓𝒚 =𝑽 𝑵𝒔𝒆𝒄𝒐𝒏𝒅𝒂𝒓𝒚 𝒔𝒆𝒄𝒐𝒏𝒅𝒂𝒓𝒚 National Grid - Electrical energy is transferred at high voltages from power stations - In domestic uses, electrical energy is transformed to lower voltages o This is done to improve the efficiency of the transmission o The larger the current, the greater the heating effect occurs in wires o So this means a large current means lots of energy is lost o So as P = IV and power is constant, increasing the voltage out of the power station and so reduces the current ▪ However high voltages are very dangerous o So when it is close to towns (etc.) the voltage is decreased (and so current increases) o This means it is safer to use ▪ As well as making sure less energy is lost as it is carried from power stations Transformer Summary - Step-up transformers increase the voltage - Step-down transformers decrease the voltage Power for a transformer with 100% efficiency: power of primary circuit = power in secondary 𝑉×𝐼 =𝑉×𝐼 𝑝𝑟𝑖𝑚𝑎𝑟𝑦 = 𝑠𝑒𝑐𝑜𝑛𝑑𝑎𝑟𝑦 https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc