5 Forces and electricity
5.4 Different circuits and
circuit diagrams
We are going to...
• use conventional symbols to draw circuit diagrams
• choose components to make circuits and compare circuits that
include batteries, switches and buzzers
• compare the brightness of lamps in series and parallel circuits
• make predictions, referring to what you know about electricity and
test to see if your predictions are correct
• describe risks when planning practical work and consider how to
minimise them and carry out practical work safely
• decide when observations need to be repeated to give more reliable results
• present and interpret results in tables
• make a conclusion from results using your understanding of electricity
• identify and classify circuits as series or parallel.
Getting started
circuit diagram
Look at the picture of a circuit. conventional symbol
1 List the components of parallel circuit
this circuit. series circuit
2 If you made a circuit to symbol
look like this, without +
– volt
–
touching the circuit, +
voltage
would the lamp light up?
3 Explain why or why not.
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5.4 Different circuits and circuit diagrams
Circuit diagrams
It takes a long time to draw a circuit like the one in the picture of
cells, lamps and switch. It is much quicker to replace the pictures
of components with signs. This is called a circuit diagram.
People all over the world can understand circuit diagrams
because everyone uses the same signs or symbols. We call them
conventional symbols because they are used by everybody. Look
at the picture at the start of this topic – this is a very complicated
circuit diagram. But imagine having to draw all the components
instead of using symbols! Here is a circuit diagram of the simple
circuit in the picture above:
Here is a list of circuit components and their symbols. In the cells
and batteries, the long lines represent the negative ends and the
short thick lines represent the positive ends.
– +
1.5V cell open switch
1.5V cells
closed switch
joined together
3V
3V battery bell
connecting wire
buzzer
bulb motor
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5.4 Different circuits and circuit diagrams
Adding different components
to a circuit
Different components need different strengths of electricity.
You can put a buzzer in a circuit instead of a lamp. But a buzzer
needs a stronger supply of electricity than a lamp.
The strength of electricity is measured in units called volts (V).
The strength of electricity that a component needs for it to work
is called the voltage.
For example, if you put a 3 V buzzer into a circuit, you need
a 3 V battery to make the buzzer work. You can make a 3 V
battery by joining two 1.5 V cells.
Think like a scientist 1
Build circuits with different components
You will need:
one 1.5 V cell, a 3 V battery, a switch, a lamp, a buzzer, connecting wires
You are going to make:
• a circuit with a cell, a lamp and a switch
• a circuit with a 3 V battery, a switch and a buzzer.
1 In your group, discuss how you will make these circuits.
Choose what components you need.
2 What are the risks when making circuits? How will you minimise these risks?
3 Predict what will happen before you make each circuit.
Make the circuit. Does the evidence support your predictions?
4 Test whether adding another cell will make the buzzer sound louder.
5 Repeat any observations you are not sure of.
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5 Forces and electricity
Continued
Questions
1 Draw a circuit diagram for each of the circuits you made.
2 Think about when you added a cell to your buzzer circuit.
What was your conclusion about the effect of this?
3 How could you make the lamp shine brighter?
4 Look at circuits A, B and C.
A B C
a Predict which circuit will work.
b Explain why the other two circuits will not work.
Series circuits
So far you have made circuits where
the electric current has only one path.
A circuit like this is called a series circuit.
Here is an example:
People often use strings of coloured lamps
connected in series to decorate trees,
buildings or rooms for festivals or parties. If one lamp does not
work, none of the lamps will light up. You have to check every
single lamp to find the faulty one.
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5.4 Different circuits and circuit diagrams
Parallel circuits
Is it possible to light up several lamps so that if one lamp burns
out the rest of the lamps will stay alight?
You can to do this if you connect the lamps so that each lamp has
its own circuit with the battery. This is called a parallel circuit.
Each pathway in a parallel circuit receives the full circuit voltage.
Find out more about parallel circuits by making one yourself in
the next investigation.
Think like a scientist 5.4.2
Make and compare a series circuit and a parallel circuit
You will need:
• plastic coated wire • 4 lamps in lamp holders • two 3 V batteries
Connect the components as shown in the drawings.
+ +
Series circuit
Parallel circuit
For each circuit:
1 Predict whether both lamps will shine. Predict whether one lamp will shine more
brightly than the other or whether they will both shine the same amount.
2 Test your prediction.
3 If you unscrew one of the lamps, predict whether the remaining lamp will shine
or not. Will it shine more brightly, the same amount or less brightly than before?
Safety: Make sure you don’t unscrew a lamp if it has been on for a while
because it will be hot and it could burn your fingers.
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5 Forces and electricity
Check your progress
1 a What units are used to measure mass?
b What unit is used to measure weight?
2 When an astronaut stands on weighing scales on Earth, the scales
read 70 kg. The astronaut travels to planet X which has half the gravitational
force of the Earth.
a What is the astronaut’s mass on Earth?
b What is the astronaut’s weight on Earth?
c What is the astronaut’s mass on Planet X?
d What is the astronaut’s weight on Planet X?
3 Describe FOUR ways in which the photograph shows the effects
of forces on the car
4 Arun and Marcus are
investigating floating and
sinking. Here are the things
they used.
a Draw a force diagram to
show a plastic toy duck floating
on water. Label the forces.
b Draw a force diagram to show a stone sinking in water. Label the forces.
c Explain why the toy duck floats and the stone sinks.
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Check your progress
Continued
5 Sofia and Zara made the circuit in the picture below:
–
+
a Draw a circuit diagram of the circuit that Sofia and Zara made.
b Identify whether this a series or a parallel circuit. Explain why.
c When they added a second buzzer to the circuit the buzzers did not work.
What could they add to the circuit to make the buzzers work?
d How could they change their circuit, without adding components,
to make the buzzers work? Draw a circuit diagram of your answer.
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