Models for teaching electric
circuits
Physics Teachers Conference
18 February 2011
Christina Hart
Making a globe light
Connect the battery and globe to
make the globe light; use connecting
wires if you need to or want to.
Find connections that:
do make the globe light?
do not make the globe light?
Draw diagrams of one connection :
where the globe does light,
where it does not.
Explain why the globe does light
with some connections but not with
others.
Making connections
filament
With a hand lens
look at the globe
Identify the filament.
Why does the globe have to be connected in a particular way
for it to light?
How are connections made from the globe holder?
How the connections made in a household light globe and
holder?
Illustrate your answers with diagrams.
Electric charge and electrical energy
Understanding how electric circuits work
depends on understanding the difference
between:
electrical energy
electric charge
These two terms are confounded in everyday
language: we talk about ‘electricity
We cannot experience electrical energy
directly: only electrically charged particles can
have electrical energy.
Electric charge and electrical energy
Electric charge and electrical energy are
different.
A charged particle (electron, proton, ion) may
carry electrical energy.
But a charged particle does not have electrical
energy just because it is charged.
Separating electrons from the atoms they
‘belong’ to requires energy.
The energy is transferred to the separated
charges: they then have electrical energy.
lightning aplet
Photo: Pym Prescott - Canberra January 27 2006: flickr.com/photos/ppym1/92003809/
Reproduced under Creative Commons Licence: http://creativecommons.org/licenses/by-nc/2.0/deed.en
Attribution-Noncommercial 2.0 Generic
Placing the switch in a circuit
Set up a simple circuit.
Predict: Where might you place a switch
to turn the globe on and off.
Mark on the diagram
Write down you reason for placing it at that
point.
Observe: Connect the switch into to the
circuit at the point you marked.
Does changing the position of the switch
make any difference to the effect of turning
it on or off?
Note:
the different positions you try
anything that surprises you
Electron flow and conventional current
In most circuits the current is
due to the movement of
(negatively charged) electrons
Electrons move from the
negative terminal of the
energy source to the positive
terminal.
Conventional current is the
equivalent flow of positive
charges, from the positive
terminal of the energy source
to the negative terminal.
Direction of
conventional
+
current
-
I
Direction of
electron flow
Model 1
The role of the battery
Conventional current
Why a complete circuit is needed
A break at any point in the circuit will stop
the flow of charges
Applet that illustrates the flow of electrons:
http://www.mste.uiuc.edu/users/Murphy/Hole
Flow/default.html
Circuits and diagrams
Experiment with connecting 2 globes, battery
and switch in different arrangements.
For each arrangement:
draw the circuit diagram;
ask your teacher to check your circuit and
diagram;
carefully note the relative brightness of the globes
and which globes are affected by the switch;
make a note of any questions you have, or
puzzling observations you notice.
Other similar activities in Brainbox kit
Electricity questions
How come, the longer the circuit or the more things
you put in it, the light comes on instantly? Speed of
electricity – how long/big could a circuit be?
Why, when the circuit has more stuff in it, does the
light fade on?
Does the number of wires matter?
Can you make circuits that ring bells/buzzers rather
than a light?
Why is the globe furthest from the battery brighter?
Shouldn’t the one nearer the battery be brighter?
Electricity questions
How does a battery work? What is the role of the
positive and negative in batteries?
Why does a battery have a positive and a negative
side, what role to positive and negative play?
Why doesn’t the battery operate when two batteries
are placed together at the flat ends? We know
positive and negative have to alternate, but unsure
what the exact reason is.
What happens when you recharge a battery?
Why are there no more power black outs any more?
Electricity questions
How does fruit conduct electricity?
Does any other food conduct electricity?
Is that why when you eat fruit/food you get
energy?
Electricity questions
Why does this stay on until we press the
switch, then it goes off?
Model 2
Current and resistance
Why the globe gets hot
Resistance at one point
in the circuit causes a
decrease in current right
round the circuit
Conductors and insulators
About practical work
At CONASTA in 1982) 1 discussed a lesson which involved a class of 12 year
old children dealing with a simple battery-bulb circuit (Osborne, 1982). The
circuit was drawn on the board (Figure 1) and the pupils were asked to
construct it. They were then required to use the circuit to identify which
common materials appeared to "conduct an electric current".
Osborne, R. (1984).
“Children's science meets scientists'
science.”
Lab Talk 28(1): 2-7.
About practical work
Figure 2 showed the circuit that was finally constructed by two of the
children, despite considerable teacher help.
What did the students find out
when they connected different
materials in their circuit?
Osborne, R. (1984). "Children's science meets
scientists' science." Lab Talk 28(1): 2-7.
About practical work
Figure 2 showed the circuit that was finally constructed by two of the
children, despite considerable teacher help.
They were very happy with
their circuit because in their
view it was important that
the light glowed every time
the switch was closed. They
found all the things they
tested were conductors.
Osborne, R. (1984). "Children's science meets
scientists' science." Lab Talk 28(1): 2-7.
About practical work
However, they seemed to have no problem in ignoring their
conclusions when the teacher's end-of-lesson conclusions were
written up on the board:
most metals unless coated with some non-conducting material will
conduct electricity, e.g. gold, aluminium, copper.
most plastic based products, e.g. foam, cellotape, plastic bags, will not
conduct electricity.
products from nature, e.g. leaves, wood, fruit pips, will generally
conduct electricity.
These statements were happily copied by the pupils into their
books. The pupils did not appear to be concerned that the teacher's
statement bore no relationship to their views and experiences;
indeed they did not even seem to be aware that this should be so.
Osborne, R. (1984). "Children's science meets
scientists' science." Lab Talk 28(1): 2-7.
About practical work
What lesson did these students
learn?
Investigating a hand-held
torch
Dismantle a battery operated hand held torch.
Identify the closed path followed by the electrons when the
torch is operating.
How does the switch operate?
Make a diagrammatic drawing of the main parts of the
torch. Show the closed circuit with a solid coloured line.
Draw the corresponding circuit diagram.
Label the main components of the torch on the circuit diagram:
A, B, C etc.
Mark the corresponding components on the diagrammatic
drawing of the torch with the same letters.
Two globe circuits
Circu it 1
Circu it 2
Circu it 3
Model 3
Resistance and current in two globe circuits
Circu it 1
Circu it 2
Circu it 3
Model 4
Energy in a simple circuit
Electrical charge vs
electrical energy
Brightness of the globe
Other analogies
Model 5
Energy in two globe circuits
Energy distribution
Current distribution
Brightness of the globes
Energy in circuits with two batteries
Circu it 1
Circu it 2
Circu it 3
Model 5 (cont)
globes with different resistance
Electricity questions
How come, the longer the circuit or the more things
you put in it, the light comes on instantly? Speed of
electricity – how long/big could a circuit be?
Why, when the circuit has more stuff in it, does the
light fade on?
Does the number of wires matter?
Can you make circuits that ring bells/buzzers rather
than a light?
Why is the globe furthest from the battery brighter?
Shouldn’t the one nearer the battery be brighter?
Electricity questions
How does a battery work? What is the role of the
positive and negative in batteries?
Why does a battery have a positive and a negative
side, what role to positive and negative play?
Why doesn’t the battery operate when two batteries
are placed together at the flat ends? We know
positive and negative have to alternate, but unsure
what the exact reason is.
What happens when you recharge a battery?
Why are there no more power black outs any more?
Electricity questions
How does fruit conduct electricity?
Does any other food conduct electricity?
Is that why when you eat fruit/food you get
energy?
The difficult bits!
Why does this stay on until we press the
switch, then it goes off?
The difficult bits!
How do electrons ‘know’ what is in the
circuit?
Model 6
Alternative models for the energy
carried by electrical charges
dominoes
bicycle chain
rope circuit
The difficult bits!
How do electrons ‘know’ what is in the
circuit
alternative models:
bicycle chain
rope circuit
Alternating current
Power supply, earth return and
electrical safety