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Electricity 2
Voltage, Potential
Difference and
Electromotive Force
Aims of the Lesson- Voltage
 Recall
the meanings of the phrases
‘potential difference’ and
‘electromotive force’
 Recall that in a series circuit the sum
of the voltages is equal to the
voltage across the whole circuit.
Voltage
 Page
118
- Worksheet on Alexandro Volta (basic
notes on voltage)
 Complete questions 9 and 10 pg 121
Total PD in a circuit
 Read
page 119 and 120
 Copy out the statement in the blue
box.
 Complete the Worksheet
‘Understanding Voltage’
Energy Saver Light Bulb
Transfers Electrical to Light and Heat
- 220 Joules of energy transferred for
every coulomb of charge passing
through
- For a current of 140 mA (0.14 A)
- 0.14 Coulombs passing through each
second
Energy = 220 / 0.14 = 1571 J
-
Aim of the Lesson
Clearly define what is meant by the
current and voltage of a circuit!
 Recall why a voltmeter is placed into
a circuit in parallel and an ammeter
is placed into a circuit in series

Eh… explain that to me please!

What does the current flowing a
circuit mean?
 What
does the voltage of a
component mean?
Number of
Coulombs
For every
Coulomb
That passes
through a
component
Going past a
point every
second
Amount of
Energy
transferred
Voltmeter action

How does a voltmeter go into a
circuit?
Equipment you
need-
First of all we
need a circuit…
What is the
Voltmeter
measuring?
Energy in and
energy out, for
each coulomb
passing through
a component
Sorry Sir but I’m gonna’ have to
search you…
What have you got on
you, Mr Coulomb?
Experiment- Investigating Voltage
How does the voltage of a component
in a series circuit compare to the
voltage of a component in a parallel
circuit?
The following two circuits are set up
and the voltage is measured across
both 1.5 V batteries and across
each 1.5V bulb individually.
Experiment- Investigating Voltage
Series
Parallel
+
+
V1
Series
V1 =
V2 =
V3 =
Parallel
V4 =
V5 =
V6 =
Investigating Voltage - Conclusion
 In
a series circuit the voltage supplied
by the battery is divided between the
components.
 In a parallel circuit the voltage
supplied is the same as the
component’s voltage.
 The energy each coulomb received
(from the battery) is equal to the total
energy given out as it goes round the
circuit (conservation of energy).
Voltage in a series circuit
If the voltage
across the
battery is 6V…
V
…and these
bulbs are all
identical…
…what will the
voltage across
each bulb be?
V
V
2V
Voltage in a series circuit
If the voltage
across the
battery is 6V…
…what will the
voltage across
two bulbs be?
V
V
4V
Voltage in a parallel circuit
If the voltage across
the batteries is 4V…
What is the
voltage here?
4V
V
And here?
V
4V
In a SERIES circuit:
Summary
Current is THE SAME at any point
Voltage SPLITS UP over each component
In a PARALLEL circuit:
Current SPLITS UP down each “strand”
Voltage is THE SAME across each”strand”
An example question:
6V
A3
3A
A1
V1
What is the
easiest path for
the Coulombs of
Charge?
All bulbs are
identical in
power rating
A2
V2
V3
Advantages of parallel circuits…
There are two main reasons why parallel circuits are used
more commonly than series circuits:
1) Extra appliances (like bulbs) can be added without
affecting the output of the others
2) If one appliance breaks it won’t affect the others
either