Doc Brown's Revision  KS3 Science

PHYSICS Unit 7J Electrical circuits

QUIZ 7J on "Electrical circuits"

What the Quiz is based on - original work schemes - programmes of study

All of KS3 Science is now under review

and the quizzes will be adapted to suit the NEW National Curriculum for KS3 Science

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In this unit pupils:

consolidate and extend their ideas about circuits

use concepts of electric current and energy transfer to explain the working of circuits

explain patterns in the measurements of current and voltage

use the concept of resistance qualitatively

build circuits in which current flow is usefully controlled

consider the hazards of electricity for humans

In scientific enquiry pupils:

explore early ideas about electric current

model current in a variety of ways

plan safe procedures and recognise hazards

use ammeters to measure current

Note on the teaching of energy

This unit applies the concept of energy to electrical circuits. In particular, pupils learn that while current is not used up in the circuit, energy is. This work focuses on distinguishing between two abstract concepts: electricity as ‘flowing stuff’ and electrical energy as something that is identified by input and output effects. Its effects are associated with the brightness of bulbs and its origins in the voltage rating of batteries. There are necessary simplifications in the treatment, as appropriate to this early unit.

This unit is expected to take approximately 8 hours.

Where the unit fits in

This unit uses ideas developed in the key stage 2 programme of study. It builds on ideas introduced in unit 6G ‘Changing circuits’ and unit 4F ‘Circuits and conductors’ in the key stage 2 scheme of work.

This unit should precede unit 8J ‘Magnets and electromagnets’ and unit 9I ‘Energy and electricity’.

Expectations

At the end of this unit

in terms of scientific enquiry

most pupils will: select and use appropriate equipment to investigate circuits which include cells, bulbs and switches; measure current; identify patterns in their results and draw conclusions about series and parallel circuits; describe hazards associated with electricity and how to deal with them

some pupils will not have made so much progress and will: explore circuits using appropriate equipment; identify patterns in their results and use these to describe the behaviour of simple circuits; identify and report on hazards associated with electricity

some pupils will have progressed further and will: plan and carry out a systematic investigation of series and parallel circuits to obtain sufficient evidence to draw conclusions; give examples of the development of scientific ideas about electricity, eg Galvani and Volta on electric current, and explain how electricity can be hazardous to humans

in terms of physical processes

most pupils will: construct a range of working electrical circuits and represent these in circuit diagrams; state that electric current is the same at all points in a series circuit and divides along the branches of a parallel circuit; use a flow model to describe resistance and to distinguish between electric current and energy transfer in a circuit; compare and contrast the advantages of series and parallel circuits in use, eg fuses, ring main

some pupils will not have made so much progress and will: construct simple electrical circuits and represent these diagrammatically; give examples of useful circuits; state safety rules for use of electricity

some pupils will have progressed further and will: relate voltage of cells and batteries qualitatively to energy transfer in circuits; use a flow model to explain the difference between electric current and energy transfer; apply the idea that nerves are electrical conductors to explain electrical hazards

Prior learning

recall that a complete circuit is required for electrical devices to work

can connect a circuit

can draw and interpret standard electrical symbols for connection, cell/battery, bulb and switch

Health and safety

Risk assessments are required for any hazardous activity. In this unit pupils:

test fuses and use high currents (at low voltage)

must not experiment with mains equipment

Model risk assessments used by most employers for normal science activities can be found in the publications listed in the Teacher’s guide. Teachers need to follow these as indicated in the guidance notes for the activities, and consider what modifications are needed for individual classroom situations.

Language for learning

Through the activities in this unit pupils will be able to understand, use and spell correctly words and phrases relating to:

circuit components, eg battery, cell, bulb or lamp, connecting wire, switch, power supply, fuse

electrical concepts, eg current, resistance, energy transfer

Through the activities pupils could:

collaborate with others to share information and ideas, and solve problems

identify the main points in each paragraph, distinguishing key points from supporting material

follow the sequence of actions, processes or ideas being described

use skimming, scanning, highlighting and note making as appropriate to different texts

Resources

Resources include:

battery-powered appliances, eg torch, motorised toy

variable resistors or potentiometers, eg dimmer controls

low-voltage model ring main and/or series lighting array

steel wool and fuse wire

water flow model of electrical circuit or alternative model

secondary sources about the work of Volta and Galvani and about the use of pacemakers and defibrillators

Out-of-school learning

Pupils could:

talk to adults about the control and safe use of domestic mains appliances, including fuses (caution them not to experiment with mains equipment)

 What happens in a circuit? •   that the nature and number of components in a circuit affects current flow •   to measure current with an ammeter •   that current in a series circuit is not used up by components •   to use the term resistance to mean opposition to flow of electricity •   Provide pupils, for work in small groups, with a battery and several identical bulbs. Ask them to explore connecting them in series, and to note patterns in their observations of the brightness of bulbs. •   Show pupils how to measure current in their circuits. Demonstrate how to connect an ammeter and how to use it carefully. Ask them to measure the current at one point in a circuit and predict the current at other places. Extend the work to include circuits with different numbers of cells. •   Draw on pupils’ experience of other electrical circuits, eg dimmer switches, and of other uses of the term ‘resistance’ to develop the qualitative idea of electrical resistance. •   Establish that the readings are constant for a given circuit, perhaps using a demonstration as a follow-up, as anomalous results can confuse pupils. Demonstrate with a variable resistor in circuit, eg dimmer switch. •  describe how increasing the number of bulbs reduces their brightness in a series circuit •  use an ammeter with care •  measure and record current in simple series circuits •  know that current does not change in a simple series circuit, that it is not ‘used up’ as it travels in the circuit •  use the term ‘resistance’ in describing circuit effects •   Check that the bulbs are matched to the voltage of the battery so that there is a change in brightness and bulbs do not ‘blow’. •   Digital ammeters are easier to read than those with analogue scales, though pupils may then find it harder to see approximately equivalent currents. Show pupils how to ensure an ammeter is not damaged in use. •   The quantitative relationship between current and resistance will be covered at key stage 4. It may be helpful to make qualitative connections with physical resistance to movement, such as friction. •   that cells and batteries are a source of electrical energy •   that a battery is a number of cells connected together with regard for polarity •   that a cell’s voltage has a chemical source •   Ask pupils the purpose of cells and batteries in a circuit. Provide cells and batteries marked with different voltages, eg 1.5, 4.5, 9V, and link their use with the concept of energy as ‘the ability to make things happen’, eg greater voltage rating, more bulbs light, so that voltage is understood simply as what makes the current flow. •   Raise the issue of polarity of cells and ask pupils to name a simple rule for connecting cells to make a battery, eg in a series positive connects to negative. Show the inside of a dry cell, identifying the connections to the positive and negative electrodes. Link the chemical origin of the cell’s voltage to pupils’ experience of ‘leaking’ and ‘dead’ batteries. •  identify a cell or battery as a source of energy •  describe why cells have positive and negative terminals, and connect them correctly in circuits •   At this stage it is sufficient for pupils to think of a battery as something that drives the current and provides the energy it carries. •   Pupils will use a voltmeter in unit 9I ‘Energy and electricity’. They will also investigate simple chemical cells.

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