charge flow, Q, in coulombs, C current, I, in ampere, A time, t, in seconds, s Define an electric current. Describe and explain why an electric current will flow in a circuit. Describe different models of electricity including: marbles moving down a ramp with masses placed on the ramp to represent rope models of electricity with knots or marks on the rope to represent electrons students modelling the electrons taking energy (sweets) from the battery (teacher) to a component (cup held by a pupil). Evaluate the benefits and drawbacks of each model. Calculate the charge flow, current or time when given the other two values. State the units used for each quantity. and also video clips available on YouTube, eg . Describe how the model represents an electric current and the limitations of the model. 6.2.1.3 The current in a series circuit. The current at any in a series circuit has the same value as the current at any 1 Draw a circuit that can be used to measure the current in a component. Investigate the current at various points within a series circuit. Does the current vary YouTube:
other point in the same circuit.. Describe how the current varies in a series circuit. Explain why the current at each in a series circuit must be the same in terms of electrons not being lost from the wire. if the ammeter is placed either side of a component? Link this idea about the current in a series circuit being the same throughout the circuit to the models of electricity looked at previously. 6.2.1.3 How the resistance of a component affects the current through it. The current through a component depends on both the resistance of the component and the potential difference across the component. The greater the resistance of the component the smaller the current for a given potential difference (p.d.) across the component. 1 Define resistance. Describe and explain how increasing the resistance in a circuit will affect the current through the circuit. What is resistance? Why are materials with low resistance chosen for power cables? What are superconductors? Model the effect of resistance on a circuit. You can do this with clear tubing and coloured water to act as the current. Pinch the tubing to show higher resistance. Investigate how increasing the resistance of a circuit affects the current. *. 6.2.1.3 How potential difference, current Current, potential difference or resistance can be 1 Use the equation to calculate the potential difference (voltage), How can the resistance of a component be calculated
and resistance are linked. Equation linking potential difference, current and resistance should be known. How to find the resistance of electrical components by experiment. calculated using the equation: potential difference, V, in volts, V current, I, in amperes, A resistance, R, in ohms, Ω Explain the design and use of a circuit to measure the resistance of a component by measuring the current through, and potential difference across, the component. Students should set up and use a circuit to investigate a factor/ the factors that affect the resistance of an electrical component(s). current or resistance when given the other two values. State the correct SI units for each quantity (potential difference, current and resistance). How does the type of metal used for a wire affect its resistance? Why do expensive leads have gold plating on them? What factors affect the resistance of a length of wire? Draw a circuit that can be used to find the resistance of an electrical component a voltmeter and an ammeter. using the current and potential difference? Why does increasing the potential difference in a circuit also increase the current? What is meant by resistance? Find the resistance of some electrical components using current and potential difference readings. Required practical: Use circuit diagrams to set up and check appropriate circuits to investigate the factors affecting the resistance of electrical circuits. This should include: • the length of a wire at constant temperature • combinations of resistors in series and parallel (10.2.15).
resistor at constant temperature. (10.2.16) *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. 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 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 carry out an investigation into how the resistance of an LDR varies with light intensity and how the resistance of a thermistor varies with temperature.
The resistance of an LDR decreases as intensity increases. LDRs including thermostats and switching on lights. *continued from the previous session. 6.2.2 Series and parallel circuits 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 practical and enquiry skills Self/peer assessment opportunities and resources Reference to past questions that indicate success 6.2.2 Series and parallel circuits. There are two ways of joining electrical components, in series and in parallel. Some circuits include both series and parallel parts. 1 Describe the differences between series and parallel circuits. Draw circuit diagrams for components connected in series and in parallel. Describe how ammeters and voltmeters are connected into a circuit Investigate series and parallel circuits: make a simple circuit containing a switch, supply and a lamp add more lamps – both in series and then in parallel note the effect on the brightness of the lamps.
6.2.3.1 Alternating and direct potential difference. Mains electricity supply. The potential difference across cells and batteries is always in the same direction. The potential difference does not change polarity. The potential difference of mains electricity changes direction. The potential difference changes polarity. Mains electricity is an a.c. supply. In the UK it has a frequency of 50 Hz and is about 230 V. 0.5 Describe the potential difference across a cell in a circuit as being in one direction only. State some common sources of a direct potential difference including cells, batteries and solar cells. Describe the potential difference of an alternating supply as changing direction. Describe mains electricity in the home in terms of potential difference, frequency and type of current. What is the difference between direct and alternating potential difference? What are common sources of direct and alternating potential difference? Research the use of direct and alternating potential difference. Find out why the USA used direct potential difference, then changed to an alternating potential difference.. Use an oscilloscope to display direct and alternating potential difference signals, or the animation on Boardworks.
6.2.4 Energy transfers 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 6.2.4.1 Electrical power and how it is calculated. Equations for electrical power should be known The of a device is related to the potential difference across it and the current through it by the equation: power, P, in watts, W potential difference, V, in volts, V current, I, in amperes, A resistance, R, in ohms, Ω 1 Define power. State the equation that links power, potential difference and current. Calculate the of an electrical appliance given the potential difference and the current. Use the equation to find any missing value given the other two. . 6.2.4.2 Energy transfers in everyday appliances Everyday electrical appliances are designed to bring about energy transfers. 0.5 What energy transfers take place in electrical appliances? Investigate a number of electrical appliances, either around the lab or well-known
Describe how different domestic appliances transfer energy from batteries or a.c. mains to the kinetic energy of electric motors or the energy of heating devices. The amount of energy an appliance transfers depends on how long the appliance is switched on for and the power of the appliance. Describe in terms of energy stores the energy transfers that are taking place in a given electrical appliance – stating which energy transfers are useful and which are wasted. Electrical appliances may be either battery or mains operated and may involve motors or heating elements. Describe how the amount of electrical energy transferred depends on the time the appliance is on for and the power of the appliance. devices, eg a TV, to look at the energy transfers that occur Investigate how the amount of energy transferred to an electrical appliance depends on the amount of time that it is on for by connecting the appliance to a joulemeter. 6.2.4.2 Work done when charge flows. Calculating the amount of energy transferred. Equations for energy transfer should be known. Work is done when charge flows in a circuit. The amount of energy transferred by electrical work can be calculated using the equation: 1 Describe how work is done when a charge in a circuit. What are the charge carriers in an electric current? How does a moving charge do work? What can moving charge do? Describe, with examples, the relationship between the power ratings for domestic electrical appliances and the changes in
energy transferred, E, in joules, J power, P, in watts, W time, t, in seconds, s charge flow, Q, in coulombs, C potential difference, V, in volts, V stored energy when they are in use. Calculate the energy transferred by an electrical appliance and rearrange the equation to find the other two values. Use the equation including rearranging the equation to find any quantity the other two. Convert into SI units where required. Use of standard form may also be required as well as understanding the meaning of the different prefixes used in a scientific context.
6.2.4.3 The National Grid. The National Grid is a system of cables and transformers linking power 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 given 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. the equation to explain why step-up transformers are used to transfer electrical power at high voltage (but low current) through the National Grid. 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 model of the national grid to show the effect of transferring energy at high and low potential differences. clip YouTube: