Physics Electricity Section 1 Circuit Symbols Section 2

Physics: Electricity Section 1: Circuit Symbols Section 2: Equations to learn Equation Charge flow = current x time Symbol equation Q=Ixt Potential difference = current x resistance V=Ix. R Power = potential difference x current P=Vx. I Power = current 2 x resistance P = I 2 x R Energy transferred = power x time E=Pxt Energy transferred = charge flow x potential difference E=Qx. V Units Charge flow - coulomb (C) Current – amperes (A) Time – seconds (s) Potential difference – volts (V) Current – amperes (A) Resistance – ohms (Ω) Power – watt (W) Potential difference – volts (V) Current – amperes (A) Power – watt (W) Current – amperes (A) Resistance – ohms (Ω) Energy = joules (J) Power – watt (W) Time – seconds (s) Energy = joules (J) Charge flow - coulomb (C) Potential difference – volts (V) Section 3: Key Terms More information Pages in revision guide: Electric current The flow of electric charge around a closed circuit. Potential difference The potential difference of a supply is a measure of the energy given to the charge carriers in a circuit. Units = volts (V). (Potential difference is the driving force that pushes charge around the circuit) Electric charge Resistance is caused by anything that opposes the flow of electric charge. Units = ohm Matter with a positive or negative charge e. g. electrons or ions. Series A circuit with only one route for charge to take. Parallel A circuit with more than one route for charge to take. Resistance

Physics: Electricity Section 4: V, I and R in Series and Parallel Components Diagram connected in… Series Current Potential Difference The current is the same at The total potential difference every point in the circuit and of the power supply is in every component. shared between the components. Itotal = I 1 + I 2 Vtotal = V 1 + V 2 Resistance Adding resistors in series increases the total resistance. The more resistors, the greater the resistance. Rtotal = R 1 + R 2 Parallel The total current through the whole circuit is the shared between the separate components. Itotal = I 1 + I 2 The potential difference Adding more resistors in across each component is parallel decreases the same. All the resistance. components get the full force potential difference Vtotal = V 1 = V 2 Section 6: Mains Electricity Alternating Current The current regularly changes direction e. g. mains electricity Direct Current The current flows in one direction only e. g. batteries. Mains Electricity UK mains is an alternating current of 230 V and at a frequency of 50 Hz. National Grid A series of cables and transformers linking power stations to consumers. Section 5: The Three Core Cable Live Brown colour. This wire provides the alternating potential difference (at about 230 V) from the mains supply. Current flows in through the live wire. Neutral Blue colour. Current taken away from appliance through this wire. It completes the circuit and has a potential difference of 0 V. Earth Yellow and green colour. This wire has a potential difference of 0 V. It is for safety as it stops the appliance from becoming live. If there is a fault, it arries charge to Earth. More information Pages in revision guide:

Physics: Electricity Section 7: Required practicals What’s the point of the practical? To find out resistance of a wire. Equation to use: 1. Investigating resistance Results: The longer the wire, the more resistance The thicker the wire, the less resistance The higher the temperature the more resistance What’s the point of the practical? To find out how current and potential difference changes in different components 2. Investigating electrical components Results: Example Apparatus Voltmeter: measures the potential difference Ammeter: measures the current Metre stick: Measures the length of wire that the current is going through Example Apparatus Voltmeter: measures the potential difference Ammeter: measures the current Resistor: what we’re testing. Can be replaced with a lamp then a diode Resistor lamp Diode What’s the point of the practical? Example Apparatus To find out what happens to the total resistance when resistors are put in series and in parallel 3. Resistors in series and parallel circuits Results for series circuits the total resistance is the same as both resistors added up. Each time you add a resistor, you get more resistance and less current Results for parallel circuits The total resistance is less than the smallest resistor. Each time you add more resistors, the current increases and the total resistance decreases. (the are more ‘routes’ overall for the current)