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neurologyYou need to know

• The standard circuit symbol for a cell is one long line and one short line, and the symbol for a battery is two or more cells connected together.
• A cell is a single source of potential difference, while a battery is two or more cells connected together to provide a larger potential difference.
• Electric charge is a property of particles, measured in coulombs, and electric current is the rate of flow of charge, measured in amperes.
• Current is calculated using `I = Q \div t`, where `I` is current in amperes, `Q` is charge in coulombs, and `t` is time in seconds.
• Potential difference is the energy transferred per unit charge between two points in a circuit, and it is measured in volts.
• Resistance is a measure of how difficult it is for current to flow through a component, and it is measured in ohms.
• Ohm’s law is `V = IR`, where `V` is potential difference in volts, `I` is current in amperes, and `R` is resistance in ohms.
• For a fixed resistor at constant temperature, current is directly proportional to potential difference, so its I–V graph is a straight line through the origin.
• For a filament lamp, resistance increases as temperature increases, so the I–V graph curves and becomes less steep at higher potential differences.
• For a diode, current flows easily in the forward direction after a threshold potential difference, but only a very small current flows in the reverse direction.
• Increasing the length of a wire increases its resistance, so for the same potential difference the current decreases.
• The resistance of a thermistor decreases as temperature increases, while the resistance of a light-dependent resistor decreases as light intensity increases.
• In a series circuit, current is the same through every component, potential difference is shared between components, and total resistance is the sum of the individual resistances.
• In a parallel circuit, potential difference is the same across each branch, current splits between branches, and total resistance is less than the resistance of the smallest individual branch.
• The UK mains supply is alternating current with a frequency of 50 hertz and a potential difference of about 230 volts.
• Direct potential difference has a constant direction, while alternating potential difference repeatedly changes direction.
• In a mains plug, the live wire is brown and carries the alternating potential difference, the neutral wire is blue and completes the circuit, and the earth wire is green and yellow and is a safety wire.
• The live wire is dangerous even when a switch is off because it can still be at a high potential difference compared with the Earth and can give an electric shock.
• Power is the rate of energy transfer, measured in watts, and one watt is one joule per second.
• Electrical power can be calculated using `P = E \div t`, `P = IV`, or `P = I^2R`, and energy transferred can be calculated using `E = Pt`.

• Draw standard circuit symbols accurately, including a cell, battery, switch, lamp, resistor, variable resistor, ammeter, voltmeter, diode, LED, fuse, thermistor and LDR.
• Draw and interpret circuit diagrams by placing components in complete loops and using correct series or parallel connections.
• Calculate current, charge or time by substituting values into `I = Q \div t` and rearranging the equation when needed.
• Calculate potential difference, current or resistance using `V = IR`, giving the answer with the correct unit.
• Investigate how wire length affects resistance by measuring potential difference and current, calculating resistance, and controlling variables such as wire material and thickness.
• Interpret I–V graphs for a fixed resistor, filament lamp and diode by linking the shape of the graph to resistance and current flow.
• Apply series and parallel circuit rules to calculate total resistance, branch currents and potential differences across components.
• Wire a mains plug safely by connecting the brown live wire to the fuse, the blue neutral wire to the neutral terminal, and the green and yellow earth wire to the earth terminal.
• Calculate energy transferred, power or time using `E = Pt`, and calculate efficiency using `\text{efficiency} = \text{useful energy output} \div \text{total energy input}`.
• Explain energy transfer in the National Grid, including how step-up transformers reduce current to reduce energy loss in transmission cables and step-down transformers make the supply safer for consumers.