Download What is a Circuit?

Year 9–10 Science Lesson Plan
What is a Circuit?
Lesson plan provided by Richard Worsey, Head of Science Faculty
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Watch out for some common misconceptions, such
as that batteries store electric charge or electrons.
Some students often think that current flows in one
direction but gradually weakens since each device
uses up some of the current. To overcome the
many misconceptions or preconceptions that
students arrive with I always model electrical
circuits.
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Electricity is the vital but mysterious provider of energy that we all take for granted.
To many students it is initially a jumble of confusing terms such
as voltage, current, amperes and ohms. One of the reasons
electricity is so difficult to understand is that the flow of charge
sample material
around a circuit cannot be seen directly… or can it?
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Background
Approach/Intentions
Introduce the topic of circuits using slide 2 of
the Boardworks presentation ‘What is a circuit’.
Explain that Benjamin Franklin proved that lightning
is linked to electricity. Benjamin Franklin was one of
the founding fathers of America, as well as a scientist,
inventor, politician and musician. You could ask students to
look into his experiments and inventions in more detail, to give
them a little bit of history mixed in with the science!
What is a C
ircuit? – Slid
e4
Using slides 3 and 4, begin with the model of the electric
circuit to help students visualise what is happening inside.
Using the concept of flow within a circuit, take it a stage
further and use the model of a coulomb travelling
through a circuit.
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Year 9–10 Science Lesson Plan
What is a Circuit?
Coulombs are lumps of electricity. They collect energy from the battery and transfer it as
they move around the circuit – this can be linked nicely to the water being pumped around
the circuit on the slide. To illustrate the transfer of energy, you could show coulombs
changing their ‘expression’ as they gain or transfer electrical energy whilst passing
between two points in the circuit. A smile changing to a frown could mean transferring
energy to other forms.
Resistance can be modelled by a part of the circuit that the coulombs have difficulty
traversing.
The diagram shows the coulombs squashing up, and hence having to transfer more
energy in order to pass through a narrow part of the circuit. Make it clear a similar result
occurs in a bulb or a resistor.
The reason I ‘lump’ the electrons into a coulomb is that now (or later on in a sequence of
lessons) electric current can be defined as a coulomb per second and electrical potential
difference as a joule per coulomb.
Once the students have an understanding of what is happening inside an electric circuit,
you can then move on to building them.
The objectives of this practical part of the lesson are to:
1)
build circuits by recognising circuit diagrams and symbols
2)
measure electric current in both series and parallel circuits
3)
realise that electric current is the same all the way around a series circuit
4)
understand how an electric current divides at a junction and be able to perform simple calculations based upon this.
Higher ability students should understand how resistance affects the size of a current and
relate this to an uneven division at a junction in a parallel circuit.
Equipment required: batteries and holders, bulbs and holders, leads, ammeters,
crocodile clips.
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Year 9–10 Science Lesson Plan
What is a Circuit?
The activities
1)
2)
Draw a circuit picture and ask students how this process could be made quicker.
Compare the time and effort involved with drawing the picture to that of drawing
the circuit with symbols. Slides 5 and 6
of the Boardworks presentation can really help here.
What is a C
ircuit? – Slid
Test the students on a selection of circuit symbols and then ask students to set a
quick test for their neighbour.
Use slide 7 as more formative assessment.
e6
Now the practical...
Before the students commence the practical work, a demonstration of how the ammeter
has to be placed into the circuit (and replacement of the wires when they have finished
the measurement) should be undertaken. The important concept this practical aims to get
across is that current is not used up by components in an electric circuit and this will need
emphasising.
Activity 1
Students set up a circuit as in the
diagram – you could display the
image below along with a circuit
diagram to help students set up.
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Year 9–10 Science Lesson Plan
What is a Circuit?
Ask students to place the ammeter in the location
on the diagram, then between the bulbs, between
the right hand side bulb and the battery and then
between the batteries – each time recording the
current.
Discuss the findings – students should find that
the current is the same at every point in the series
circuit.
What is a C
ircuit? – Slid
e7
In order to reinforce this teaching point, you could place
two different voltage bulbs in series and compare their
brightness. Measure the current before and after the bulbs to
prove that this is the same. Swap the bulbs around and repeat for
further emphasis.
Activity 2
Now ask students to measure the
current at various points in a parallel
circuit.
Use the results to discuss current
addition in parallel circuits Kirchoff’s Current Law.
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Year 9–10 Science Lesson Plan
What is a Circuit?
Taking it Further
The natural extension of this lesson is to take a look at how switches placed at different
points in series and parallel circuits can control different bulbs.
At this stage, move to using only circuit diagrams. Faster working members of the group
could investigate how shortening a length of resistance wire placed in the circuit affects the
measured current. Make sure students take care as the wire will get hot.
Outcomes/Benefits
If the learning objectives have been achieved, students will now understand that electric
current is a flow of charge that possesses electrical potential energy obtained from a
battery or other power source. They will be able to explain the behaviour of electric current
in series and parallel circuits, and at an extension level, how resistance affects electric
current.
Questions for homework:
Have you ever noticed that if you switch off your bedroom light, the light in another room
remains unchanged? This is because your home is wired in parallel.
1) Design a mains circuit that supplies three rooms with electric lighting. Each room has a `
switch to control each light. Draw a simple circuit in your book.
2) Design a circuit that will switch on:
- two lights in one room from one switch
- one light in another room from one switch.
Draw these circuits in your book.
You could ask students to build and test their circuits in the next lesson.
From circuits to cells, Boardworks Science
resources contain a wealth of ready-made, fully
customisable resources to help your students
achieve their full potential.
To see it in action, try our online interactive
sample:
http://www.boardworks.co.uk/science-year-710_
874/product-samples
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Boardworks Ltd
The Gallery
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Oxford, OX4 1LF
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t: +44 845 0 300 400
f: +44 845 0 300 200
[email protected]
www.boardworks.co.uk