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GE6: Modelling the behaviour of Electric Circuits I’m happy with this Ge6.1 1. 2. 3. 4. Ge6.2 1. Where are the charges in circuits and how can they be made to move? appreciate that electric current is a flow of charge; . explain that in an electric circuit the components and wires are full of electrons that are free to move; explain that when a circuit is made the battery causes these free electrons to move, and that they are not used up but flow in a continuous loop recall that in metallic conductors an electric current is a movement of free negatively charged electrons What determines the size of the current in an electric circuit? explain that the larger the voltage of the battery, the bigger the current. 2 recognise that components (such as resistors, bulbs, motors) resist charge flowing through them; 3 relate the resistance of the components, to the current through them; 4 appreciate that the resistance of connecting wires is so small that it can usually be ignored; 5 recall that resistors are heated when electric current passes through them; 6 describe how a bulb filament gets hot enough to glow, and that this heating effect is caused by collisions between the moving charges and stationary atoms in the wire. 7 8 Ge6.3 explain that two (or more) resistors or lamps in series have more resistance than one on its own because the battery has to push charges through both of them; explain that two (or more) resistors in parallel provide more paths for charges to flow along than one resistor on its own so the total resistance is less, and the current is bigger. How do parallel and series circuits work? What is voltage? I need help with this 1 2 3 recognize that potential difference is another term for voltage; relate the potential difference (voltage) between two points in the circuit to the energy transferred to, or from, a given amount of charge as it passes between these points; describe the effect on voltage and current of adding further batteries in series and in parallel with original one. How does potential difference (voltage) behave in a series circuit? appreciate that when several components are connected in series to a battery: the current through each component is the same; 4 the potential differences across the components add up to the potential difference across the battery (because the total energy transferred to each unit of charge by the battery must equal the amount transferred from it to other components); explain that the potential differences across the components are in direct proportion to their resistance values, because more energy is transferred by the charge passing through a large resistance than through a small one. How does current behave in a parallel circuit? . Candidates should be able to apply these ideas to describe and explain simple features of domestic mains electric circuits in particular safety devices, fuses, earth and RCDs (all devices at same operating voltage, each independently switched). appreciate that when several components are connected in parallel directly to a battery: the potential difference (voltage) across each component is equal to the voltage of the battery; 5 Ge6.4 the current through each component is the same as if it were the only component present; the total current from (and back to) the battery is the sum of the currents through each of the parallel components. How is mains electricity produced? How are voltages and currents induced? . 1 recall that mains electricity is produced by generators; recall that generators produce a voltage by a process called induction; 2 recall that when a magnet is moving into a coil of wire a voltage is induced across the ends of the coil; 3 4 recognise that if the ends of the coil are connected to make a closed circuit, a current will flow round the circuit; recall that if the magnet is moving out of the coil, or the other pole of the magnet is moving into it, there is a voltage induced in the opposite direction. describe how in a generator, a coil of wire is rotated in a magnetic field (or a magnet is rotated within a coil of wire) to induce a voltage across the ends of the coil; understand that the size of this induced voltage can be increased by: 5 increasing the speed of rotation of the coil (or the magnet); increasing the strength of the magnetic field; increasing the number of turns on the coil; placing an iron core inside the coil. explain, when provided with an appropriate diagram, why a generator has brushes and slip rings, and how these work. 6 7 8 9 10 11 How is mains electricity generated? describe how the induced voltage across the coil of a generator changes during each revolution of the coil and explain that the current produced in an external circuit is an alternating current (a.c.); appreciate that the current from a battery always travels in the same direction: it is a direct current (d.c.); recall that mains electricity is an a.c. supply; appreciate that a.c. is used because it is easier to generate, and can be distributed more efficiently, than d.c; recognise that the mains supply voltage to our homes is 230 volts. note Ge6.5 How much electrical energy do we use at home? Candidates will not need to recall any details of d.c. generators. Details of transmitting power at high voltage are not required. How do voltage and current affect electrical energy? use the following equation to calculate energy transfer in joules and kilowatt-hours: 1 energy transferred = power × (joules, J) (watts, W) (kilowatt hours, kWh) (kilowatts, kW) time (seconds, s) (hours, h) Transformation of these equations is only required on the higher tier. 2 appreciate that when electric charge flows through a component (or device), energy is transferred to the component; state and be able to use the equation: 3 power = (watts, W) potential difference (voltage) × current (volts, V) (amperes, A) How much does my electricity cost? 4 explain that a joule is a very small amount of energy, so a domestic electricity meter measures the energy transfer in kilowatt hours; 5 calculate the cost of electrical energy given the power, the time and the cost per kilowatt hour; 6 state and be able to use the equation in the context of different electrical appliances: efficiency = energy usefully transferred total energy supplied