Why are circuit symbols used? How are the electrical components connected together to form a circuit? What happens to the energy store of a cell/battery when it is connected into a circuit? Play generation game with the circuit symbols shown on a PowerPoint. Give pupils 2 minutes to draw and label all of them – allow less time for more able pupils. 4.2.1.2 Electric currents are the flow of charge. Equation for electric current as the rate of flow of charge should be known. For electrical charge to flow through a closed circuit the circuit must include a source of potential difference. Electric current is a flow of electrical charge. The size of the electric current is the rate of flow of electrical charge. Charge flow, current and time are linked by the equation: 1 Define potential difference. State the name of the particle that carries the electrical charge round a circuit. Ask questions such as: What is an electric current? particle moves to cause an electric current? What makes the particle move? Define an electric current. Demonstrate models of electricity and discuss what each part of the model represents and what makes the particles move. Examples could include the rope model, sweets model, water flow model, etc. Model the flow of an electric current using various models and also video clips available on YouTube, eg .
calculation or graphical methods. Analyse the results of the investigation to describe and explain how the resistance is affected. 4.2.1.4 Ohm’s law and the conditions needed for it to apply. Current-potential difference graphs for electrical components. The current through an ohmic conductor (at a constant temperature) is directly proportional to the potential difference across the resistor. This means that the resistance remains constant as the current changes. 1 Define what is meant by an ohmic conductor. What components are ohmic conductors? Describe the conditions for which Ohm’s law is valid. Explain why Ohm’s law is not when the temperature of the conductor increases in terms of collisions. Draw the I-V graph for an ohmic conductor. Explain the shape of the I-V graph of the ohmic conductor. Find the resistance of a resistor by experiment. Plot an I-V graph for the resistor, disconnecting the power supply unit between readings to let the resistor cool down. Calculate the resistance from the graph and compare with the known value from the colour coding on the resistor. 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. (8.2.4)
*This activity is spread over two sessions. 4.2.1.4 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 light intensity increases. 1.5 Draw the I-V graphs for a filament lamp and a diode. Explain the 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 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. (8.2.4) 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.
*continued from the previous session. 4.2.2 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 apply practical and enquiry skills Self/peer assessment opportunities and resources Reference to past questions that indicate success 4.2.2 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, power supply and a lamp add more – both in series and then in parallel note the effect on the brightness of the lamps.
Use the concept of equivalent resistance. 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. 4.2.2 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 total resistance of two resistors is less than the resistance of the smallest individual resistor. 1 State that the potential difference across each component in a parallel circuit is the same. Describe how the currents in different 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 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. 4.2.2 Resistance in series and in parallel circuits. Students should be able to explain qualitatively why adding resistors in series increases the 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 terms of increased number of pathways. Find out some factors that affect the resistance of a wire. 4.2.3 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
objects that carry different types of charge attract. Attraction and repulsion between two charged objects are examples of force. one positively charged and one negatively charged object placed near each to each other. One possible way is to charge a plastic rod by rubbing with a cloth then place the rod on a watch glass that is free to rotate. Placing a second charged rod near the first should get the first rod to attract or repel from the second rod.