Scheme of work Combined Science: Trilogy - Foundation Physics – Electricity This resource provides guidance for teaching the Electricity from our new GCSE Combined Science: Trilogy/Physics (8464). It has been updated from the draft version to reflect the changes made in the accredited specification. There are many changes throughout the document. The scheme of work is designed to be a flexible medium term plan for teaching content and development of the skills that will be assessed. It is provided in Word format to help you create your own teaching plan – you can edit and customise it according to your This scheme of work is not exhaustive; it only suggests activities and resources you could find useful in your teaching. 6.2 Electricity 6.2.1 Current, potential difference and resistance Spec ref. Summary of the specification content Learning outcomes What most candidates should be able to do Suggested timing (hours) Opportunities to develop Scientific Communication skills Opportunities to develop and apply practical and enquiry skills Self/peer assessment opportunities and resources Reference to past questions that indicate success 6.2.1.1 How to draw circuit symbols. Circuit diagrams use standard symbols: 0.5 Recall circuit symbols. Identify circuit symbols used in a circuit. Construct circuit diagrams using standard symbols. Set up simple circuits from circuit diagrams. Circuits need to include voltmeters and ammeters so that students are aware of how these devices are connected.
*This activity is spread over two sessions. 6.2.1.4 How the resistance of electrical components change with external conditions. Current-potential difference graphs for electrical components. The resistance of components such as filament lamps, diodes, thermistors and LDRs is not constant; it changes with the current through the component. The resistance of a filament lamp increases as the temperature of the filament increases. The current through a diode flows in one direction only. The diode has a very high resistance in the reverse direction. The resistance of a thermistor decreases as the temperature increases. The resistance of an LDR decreases as intensity increases. 1.5 Draw the I-V graphs for a filament lamp and a diode. Explain the shape of the resulting graph in terms of resistance and current. Draw graphs to show how the resistance of an LDR will vary with light intensity and of a thermistor with temperature. Why do the current-potential difference graphs for diodes and filament lamps look different to that of an ohmic conductor? Calculate the resistance of an LDR or a thermistor given the range of resistances for that component and the conditions that it is placed in. Describe and explain real world applications of thermistors and LDRs including thermostats and switching on lights. Required practical *: Use circuit diagrams to construct appropriate circuits to investigate the I–V characteristics of a variety of circuit elements including a filament lamp, a diode and a resistor at constant temperature. (10.2.16) Plot the graphs for these components and explain the resulting shape in terms or resistance. Plan and out an investigation into how the resistance of an LDR varies with light intensity and how the resistance of a thermistor varies with temperature.
Why are decorative lights for Christmas trees connected in parallel and not series? Why does adding additional lamps in series, make them all dimmer? Current through, and potential difference across, each lamp can be measured to get numerical values and see the effect of adding more lamps. 6.2.2 Properties of series circuits and adding resistors in series. For components connected in series: there is the same current through each component the total potential difference of the power supply is shared between the components. the total resistance of two components is the sum of the resistance of each component. resistance, R, in ohms, Ω 1 Explain why the current through each component in a series circuit is the same. Why does adding more lamps in series cause the current to decrease? What is resistance? Describe how the potential difference of the power supply is shared between the components and that the share of the potential difference a component receives depends on the resistance of that component. Calculate the resistance or two components in a circuit Investigate series circuits to find out how adding resistance, in the form of a variable resistor, changes the current and the potential difference.
Use the concept of equivalent resistance. Apply knowledge of series circuits to real world applications. Students should be able to explain the design and use of d.c. series circuits for measurement and testing purposes. 6.2.2 Properties of parallel circuits including giving the upper limit of resistance when resistors are added in parallel. For components connected in parallel: the potential difference across each component is the same the current through the whole circuit is the sum of the currents through the separate components the resistance of two resistors is less than the resistance of the smallest individual resistor. 1 that the potential difference across each component in a parallel circuit is the same. Describe how the currents in different parts of a parallel circuit change and give the reasons for this change. Describe the effect on the resistance of adding resistors in parallel. State that adding resistors in parallel will make the total resistance less than the lowest value resistor. Describe the differences between series and parallel circuits in terms of current and potential difference. Investigate how the current in each loop of a parallel circuit compares to the current in the main branch of the circuit. Investigate the effect of adding two resistors in series in a simple circuit, then adding the same resistors in parallel in the same circuit. Find the resistance of three resistors in parallel by experimental methods.
Students are not required to calculate the total resistance of resistors placed in parallel. 6.2.2 Resistance in series and in parallel circuits. Students should be able to explain qualitatively why adding resistors in series increases the total resistance, while adding resistors in parallel decreases the total resistance. 0.5 What causes resistance? Research what resistance is and why some materials have no resistance (superconductors). Explain why adding resistors in series to a circuit, increases the resistance of that circuit in terms of number of collisions. Explain why adding resistors in parallel decreases the resistance of a circuit in of increased number of pathways. Find out some factors that affect the resistance of a wire. 6.2.3 Domestic uses and safety Spec ref. Summary of the specification content Learning outcomes What most candidates should be able to do Suggested timing (hours) Opportunities to develop Scientific Communication skills Opportunities to develop and apply practical and enquiry skills Self/peer assessment opportunities and resources Reference to past questions that indicate success
6.2.4.3 The National Grid. The National Grid is a system of cables and transformers linking stations to consumers. Electrical power is transferred from power stations to consumers using the National Grid. Step-up transformers are used to increase the potential difference from the power station to the transmission cables then step-down transformers are used to decrease, to a much lower value, the potential difference for domestic use. This is done because, for a power, increasing the potential difference reduces the current, and hence reduces the energy losses due to heating in the transmission cables. 1 Describe how electrical power is transferred from the power stations to the consumers via the National Grid. Students will need to be able to give the types of transformer used and describe how the potential difference in the wires changes at each stage of the process. How does electricity get from the power station to our homes? A large potential difference is dangerous. Why is the electricity sent at a high potential difference rather than a low p.d.? How do transformers work? What do substations do? Explain how the National Grid system is an efficient way to transfer energy. Why is it more economical to transfer through the National Grid at high potential differences rather than using lower and potentially safer potential differences? Model the National Grid to show how electricity is sent from power stations to consumers. Demonstrate how transformers work and where they are placed in the National Grid. Demonstrate a of the national grid to show the effect of transferring energy at high and low potential differences. Video clip YouTube: