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neurologyYou need to know

• Standard circuit symbols include a cell, battery, switch, lamp, fixed resistor, variable resistor, diode, light-emitting diode, thermistor, light-dependent resistor, fuse, ammeter and voltmeter.
• 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 matter measured in coulombs, C, and electric current is the rate of flow of electric charge measured in amperes, A.
• Electric current is calculated using `I = Q \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, V.
• Resistance is a measure of how difficult it is for current to flow through a component, and it is measured in ohms, `\Omega`.
• For an ohmic conductor at constant temperature, potential difference, current and resistance are linked by `V = I R`.
• Increasing the potential difference across a component usually increases the current through it, while increasing the resistance decreases the current for the same potential difference.
• The resistance of a wire increases as its length increases, so a longer wire gives a smaller current for the same potential difference.
• An ohmic conductor has a straight-line current-potential difference graph through the origin when its temperature is constant.
• A filament lamp has increasing resistance as current increases because its temperature rises, giving a curved current-potential difference graph.
• A diode allows current to flow easily in one direction but has very high resistance in the reverse direction.
• The resistance of a thermistor decreases as temperature increases.
• The resistance of a light-dependent resistor decreases as light intensity increases.
• In a series circuit, components are connected in one loop, so the current is the same through every component, the total potential difference is shared, and the total resistance is the sum of the component resistances.
• In a parallel circuit, components are connected in separate branches, so the potential difference is the same across each branch, the total current is shared between branches, and the total resistance is less than the smallest branch resistance.
• The UK mains supply is an alternating potential difference with a frequency of 50 Hz and a potential difference of about 230 V.
• Direct potential difference has one fixed direction, while alternating potential difference repeatedly changes direction.
• In a UK 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 connected to the metal case.
• The National Grid uses step-up transformers to increase potential difference and reduce current for efficient transmission, then step-down transformers to reduce potential difference for safe use by consumers.

• Draw accurate circuit diagrams using standard symbols, with components connected by straight wires and no unnecessary gaps.
• Interpret circuit diagrams by identifying whether components are in series or parallel and predicting the current, potential difference and resistance relationships.
• Calculate current, charge or time by rearranging and substituting into `I = Q \t` with correct units.
• Calculate potential difference, current or resistance by rearranging and substituting into `V = I R` with correct units.
• Investigate how the length of a wire affects resistance by measuring current and potential difference for different wire lengths while controlling material, thickness and temperature.
• Plot and interpret current-potential difference graphs for components such as an ohmic conductor, filament lamp and diode.
• 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.
• Calculate energy transferred using `E = P t` or `E = Q V`, and calculate efficiency using `efficiency = useful energy output \div total energy input`.
• Calculate power using `P = E \t`, `P = I V`, selecting the correct equation for the information given.
• Draw electric field patterns around charged particles, showing arrows away from positive charges and towards negative charges.