CP9 Electricity and Circuits

CP9 Electricity and Circuits

• CP9a Electric Circuits:
  • Atoms are made up of protons, neutrons, and electrons.
  • Electrical symbols are used to represent electrical components in circuits (e.g., cells, switches, voltmeters, ammeters, lamps).
  • Circuit diagrams use conventions for positive and negative terminals.
  • Identical lamps in series have different brightness levels than identical lamps in parallel.
  • The number of lamps, cells, or switches affects the brightness and current in series or parallel circuits.

CP9b Current and Potential Difference

• Measuring Voltage: How to measure voltage.
• Potential Difference: Definition of potential difference.
• Measuring Current: How to measure current.
• Electric Current: Conditions needed to produce an electric current (a complete circuit and a voltage source).
• Current at a Junction: Behavior of current at a junction.

CP9c Current, Charge, and Energy

• Potential Difference, Charge, and Energy Transfer: Link between potential difference (voltage), charge, and energy transferred across a battery or component.
• Volt: Unit of potential difference (energy transferred per coulomb).
• Energy Transfer Equation: Equation relating energy transferred, charge, and potential difference (E = Q × V).
• Electric Current and Electric Charge: Link between electric current and electric charge.
• Current in Metals: Explanation of electric current in metals based on electrons.
• Charge, Current, and Time Equation: Equation relating charge, current, and time (Q = I × t).

CP9d Resistance

• Resistance and Variable Resistors: Effects of changing resistance in a circuit, variable resistors.
• Potential Difference, Current, and Resistance Equation: Potential difference (V) = current (I) x resistance (R), (V=I x R).
• Resistances in Series and Parallel: Why net resistance increases in series and decreases in parallel.
• Series Circuits Calculation: Calculating currents, potential differences, and resistances in series circuits.
• Series Circuits Design: Design and construction of series circuits for testing.

CP9e More About Resistance

• Resistance Variation: How current varies with potential difference for filament lamps, diodes, fixed resistors, LDRs, and thermistors.
• Light-Dependent Resistor (LDR): How resistance changes with light intensity.
• Thermistors: How resistance changes with temperature (negative temperature coefficient).
• Filament Lamps, Diodes, LDRs, Thermistors Explaining how to investigate the relationships between potential difference, current, and resistance for different circuit components.

CP9f Transferring Energy

• Energy Transfer in Resistors: Energy transfer in resistors when there's an electric current.
• Thermal Energy Dissipation: Explanation that electrical energy is dissipated as thermal energy in the surroundings.
• Electron-Ion Collisions: Energy transfer in circuits due to collisions between electrons and ions in the lattice.
• Low Resistance Wires: Ways to reduce unwanted energy transfer through low resistance wires.
• Heating Effect Advantages and Disadvantages: Advantages and disadvantages of the heating effect of an electric current.
• Equation for Energy Transfer: Energy transferred (joules) = current (amps) x potential difference (volts) x time (seconds)

CP9g Power

• Power Explanations: Power described as energy transferred per second, with watts as the unit.
• Power Equation using Energy and Time: Power (watts) = energy transferred (joules) / time taken (seconds).
• Power Equations for Circuits: Electrical power equations relating power, current, voltage (P = I x V) and current, resistance (P = I² x R).

CP9h Transferring Energy by Electricity

• Energy Transfer in Devices: Mechanisms for energy transfer in various domestic devices (motors, heating devices).
• Direct and Alternating Voltage: Differences between direct current (DC) and alternating current (AC).
• Domestic AC Supply: Explanation of the UK's domestic supply (AC, frequency, and voltage).
• Electrical Appliances and Storage: The relationship between power ratings of domestic appliances and changes in stored energy.

CP9i Electrical Safety

• Live, Neutral, and Earth Wires: Explanation of the differences in function between live, neutral, and earth wires.
• Earth Wire Function: Function of an earth wire.
• Fuses and Circuit Breakers: Fuses and circuit breakers in ensuring safety within a circuit.
• Switch and Fuse Connections: Explanation of why switches and fuses should be connected to the live wire in residential circuits.
• Potential Differences (Live, Neutral, Earth): Explanation of the potential differences between the live, neutral, and earth mains wires (live=230V, neutral=0V, earth=0V)
• Live-Earth Connection Dangers: Dangers of providing a connection between the live wire and the earth.