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neurologyYou need to know

• A cell is a single source of potential difference, while a battery is two or more cells connected together.
• Electric charge is a property of particles that can be positive or negative, and charge is measured in coulombs, C.
• Electric current is the rate of flow of electric charge, and current is measured in amperes, A.
• 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 work done per unit charge between two points in a circuit, and it is measured in volts, V.
• Resistance is opposition to the flow of current, is measured in ohms, `\Omega`, and is calculated using `R = V \div I`.
• For a fixed resistance, increasing the potential difference increases the current; for a fixed potential difference, increasing the resistance decreases the current.
• In a metal wire, increasing the length of the wire increases its resistance and reduces the current for the same potential difference.
• An ohmic conductor has a current directly proportional to potential difference when its temperature is constant, so its IV graph is a straight line through the origin.
• A filament lamp has increasing resistance as current increases because the filament gets hotter, so its IV graph curves and becomes less steep.
• A diode has a very high resistance in the reverse direction and allows current to flow mainly in the forward direction.
• A thermistor has a resistance that decreases as temperature increases.
• A light-dependent resistor has a resistance that decreases as light intensity increases.
• In a series circuit, the current is the same through every component, the total potential difference is shared between components, and the total resistance is the sum of the component resistances.
• In a parallel circuit, the potential difference is the same across each branch, the total current is the sum of the currents through each branch, and adding branches decreases total resistance.
• The UK mains supply is alternating current at about 230 V and 50 Hz.
• Direct potential difference has one constant direction, while alternating potential difference repeatedly changes direction.
• In a UK mains plug, the live wire is brown, the neutral wire is blue, and the earth wire is green and yellow.
• The live wire carries the alternating potential difference from the supply, the neutral wire completes the circuit, and the earth wire is a safety wire connected to the metal case of an appliance.
• The live wire is dangerous even when an appliance switch is off because it can still be at a high potential difference relative to the earth and can give an electric shock if touched.

• Draw standard circuit symbols accurately, including cells, batteries, switches, lamps, resistors, variable resistors, ammeters, voltmeters, diodes, thermistors, LDRs and fuses.
• Draw and interpret circuit diagrams by identifying components, tracing complete paths for current, and distinguishing series and parallel sections.
• Calculate current, charge or time using `I = Q \div t`, including rearranging the equation and using correct units.
• Calculate potential difference, current or resistance using `V = I R`, including rearranging the equation and using volts, amperes and ohms.
• Investigate how wire length affects resistance by measuring potential difference and current for different lengths of wire, controlling variables such as wire material and thickness, and calculating resistance.
• Interpret IV characteristic graphs for ohmic conductors, filament lamps and diodes by describing how current changes with potential difference and linking gradient to resistance.
• Wire a UK mains plug safely by connecting the brown live wire to the fuse terminal, the blue neutral wire to the neutral terminal, and the green-yellow earth wire to the earth terminal, with the cable grip holding the outer insulation.
• Calculate energy transferred using `E = P t` or `E = Q V`, selecting the correct equation from the quantities given and using joules, watts, seconds, coulombs and volts.
• Calculate efficiency using `\text{efficiency} = \text{useful energy output} \div \text{total energy input}` or `\text{efficiency} = \text{useful power output} \div \text{total power input}`.
• Calculate electrical power using `P = E \div t`, `P = I V` or `P = I^2 R`, and explain that power is the rate of energy transfer.