1. Content P2.3 - P2.4
Currents in electrical circuits
Lesson 1
What is static electricity?
Lesson 2
What is electrical current?
Lesson 3
Series and parallel circuits
Lesson 4
Resistance & Ohm’s Law
Lesson 5
Investigating resistance
Lesson 6
How LDR and thermistors work

2. Content P2.3 - P2.4
Currents in electrical circuits
Lesson 7
Potential difference
Lesson 8
Current in series & parallel circuits
Lesson 9
The heating effect of current
Lesson 10
Electrical power
Lesson 11
Mains electricity
Lesson 12
Fuses and circuit breakers

3. Lessons 4
Resistance
Ohm’s Law
Rich question:
Can we control
electricity? How?
Agree learning outcomes
D/E
1. State that the components (motors, bulbs,
wires etc.) in a circuit resist the flow of
charge. The bigger the resistance, the
smaller the current.
C
2. Describe how to find the resistance of a
component by measuring the current
through, and the potential difference across,
the component
3. Calculate potential difference (V) using
current (I) and resistance (R)
B
4. Describe the relationship between the
current through and potential difference
across a resistor (at a constant temperature)
as directly proportional (*also use a graph)
A/A* 5. Use a model to explain how the resistance
changes in terms of ions and electrons
linking ideas to length of wire, thickness &
temperature.

5. What is my obstacle to learning?

7. What does this word
mean in Physics?
Other words with
similar meanings are…
11 December 2013
Why do we need mood lighting?
What is the science behind this
idea? [metal ions, electrons, collide]

8. Stage lighting engineer wanted
Your mission – To design a lighting scheme for my
new show coming to Stratford.
Specification:
1. You must be able to set up and draw a simple
circuit for making mood lighting.
2. Explain how it works using the idea of
resistance. Use the words ‘metal ions and
electrons’.
3. Use an analogy to explain to me so that I can
understand why the bulb changes brightness.

9. Present new information
Electricity in wires is a flow of electrons along the wire. As the
electrons move along the wire they collide with the metal ions. These
collision make the atoms vibrate more…which makes the metal hotter.

10. Electron flow and resistance
Resistance is a measure of how much a material tries
to stop electricity passing through it.
All wires and devices have some resistance, which is why
electrical appliances always waste some energy as heat.
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11. Investigating current and voltage
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12. Construct meaning
What is the
explanation
?
How does changing
the length of wire in
this variable
resistor affects the
bulb?

13. Apply to demonstrate

14. When the length of the wire increases…
The effects:
• The brightness of the bulb…
• The size of current…
• The wire feels…
The cause:
• This is because, the number of
metal ions...
• It is harder for the electrons to
flow through the wire as there
are more ……………… with the
metal ions of the wire.

15. Factors that affect resistance
The resistance of a wire depends on several factors:
 Material – Different materials have different resistances
because some materials are better conductors. Nichrome
wire has a higher resistance than a copper wire of the
same size.
 Length – The longer a wire is the higher its resistance.
When electrons travel down a long wire they can collide
with more metal ions than in a short wire.
 Thickness – A thin wire has a higher resistance than a
thick wire.
 Temperature – The higher the temperature of a wire the
higher its resistance. Metal ions vibrate more at higher
temperatures and so collisions with electrons are more
likely to happen.
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16. Review
What is resistance?

17. How are current and voltage related for a resistor?
Set up this circuit with a resistor and a variable resistor.
voltage
(V)
0
0.5
1.0
A
V
Slowly move the variable resistor
so that the voltage increases by
0.5 V and record the current for
each setting.
current
(A)
0
0.6
1.1
1.5
1.8
2.5
3.0
2.0
2.5
3.0
3.5
3.5
4.2
Plot a current-voltage graph of the results.
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18. The graph is a straight line so
the two quantities current and
voltage are proportional.
So if voltage doubles then the
current doubles and so on.
x
x
x
x
x
Plot the current and voltage
readings for a resistor on a
graph and draw a line of best fit.
Current / A
Current-voltage graph for a resistor
x
x
x
Potential difference / V
This is called Ohm’s Law after the scientist Georg Ohm.
Ohm’s Law
The current flowing through a wire is proportional
to the potential difference (voltage) across it
provided the temperature remains constant.
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19. Current-voltage graphs for different wires
The copper wire has a steeper
gradient and so has a lower
resistance than the nichrome.
x
Current / A
The points produce straight
lines with different gradients.
copper
x
x
x
x
Plot the current and voltage
readings for nichrome and
copper wires of the same size.
x
x
x nichrome
x
x x
x
Potential difference / V
At the same potential difference, a copper wire lets a
larger current flow than a nichrome wire of the same
length and thickness.
The steeper the gradient of a current-voltage graph,
the lower the resistance of the wire.
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20. Current-voltage graphs for a bulb
Increasing the voltage across
the filament in the bulb causes
this wire to get very hot and
give out light.
x
Current / A
The graph produced is not a
straight line but a curved line.
x
x
x
Plot the current and voltage
readings for a filament bulb.
x x
x
x
Potential difference / V
As the wire gets hotter, its resistance gets higher, which
means the current flow is less. So as the temperature
rises the current is not proportional to the voltage.
The higher the temperature of a wire,
the higher its resistance.
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21. Current-voltage graphs and Ohm’s Law
Which of the components obeys Ohm’s Law?
I
1
I
2
I
3
V
V
V
1. A wire or
resistor
2. A filament
lamp
3. Wires of
different
materials

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22. Resistance – true or false?
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23. P2 REVISION – CHAPTER 4 – Current Electricity
Electrical Charges
If you rub two electrically
insulating materials are rubbed
together, __________________
are rubbed off one material and
deposited on the other.
Objects that have opposite electric
charges ______________ each
other, if they have the same
electric charge they___________.
Electric Circuits
Electric symbols
I is the current in amperes, A
Q is the charge in coulombs, C
t is the time in seconds, s.
Every component has an agreed circuit
symbol.
Make sure you can recognise and draw
them!
Resistance
Current is measured with an ammeter. Where are ammeters placed in relation to the
component?
What is the unit of current?
The potential difference(pd) across a component is measured with a voltmeter. These
are always placed in parallel with the component. What is the unit of potential
difference?
V is ?
W is ?
Q is ?
Don’t forget units!
R is ?
V is ?
I is ?
Don’t forget units!
Ohm’s law: states that the current through a resistor at constant temperature is
directly proportional to the potential difference across the resistor.
KEY WORDS:
Insulating
Electron
Attract
Repel
Resistance
Series
ASSESSMENT:

24. P2 REVISION – CHAPTER 4 – Current Electricity Cont.
Series Circuits
Current-Potential Difference Graphs
A current-potential difference
graph for a resistor.
How are the components connected in a series circuit?
What happens if there is a break in the circuit?
Is the current the same or different through each component?
If you add together the potential difference what does it give you?
The resistance of the individual
components add up to give the
total resistance of the circuit.
A current-potential difference
graph for a filament bulb, line is
a curve so the current is not
directly proportional to the
__________________
___________________.
The current in a diode flows
in one direction only, in the
reverse direction the diode
has a very high resistance so
the current will be what?
Parallel Circuits
How are the components connected in a series circuit?
What happens if there is a break in the circuit?
Is the pd across each component the same or different?
The bigger the resistance of a component, the ______________ the current through it.
Use this equation to work out the
current through a component in a
parallel circuit.
Thermistor: Resistance _______________ if its temperature
increases.
LDR: resistance decreases if the light intensity on it ___________.
KEY WORDS:
Diode
Filament bulb
Resistor
Thermistor
ASSESSMENT:

25. P2 REVISION – CHAPTER 5 – Mains Electricity
Alternating Current
Direct current is supplied by cells and
batteries and passes round the circuit in
one direction.
Alternating current is from the mains,
how does it travel?
Frequency of am ac supply can be
worked out from an oscilloscope trace
using the equation:
Cables & Plugs
Fuses
How does a fuse work?
Where is a fuse fitted in a circuit?
Electrical Energy & Charge
An electric current is the flow of what?
What is the equation that relates to charge, current and time?
When charge flows through a resistor, what makes it hot?
How does a circuit breaker work?
What can you use this equation for?
Electrical Power & Potential
Difference
Electrical Issues
Electrical faults are dangerous what two things can they cause?
Power can be calculated using the
above equation.
Why are the pins of a plug made of
brass?
What does the earth wire earth?
Why are some cables thicker than
others?
Using the current and the pd and the
equation above enables us to
calculate the power of an appliance.
To work out the correct rating in
amperes for a fuse rearrange the
above equation, what would the
equation now be?
Why must you check cables, plugs and sockets for damage
regularly?
What must you not touch with wet hands?
Why are filament bulbs very inefficient?
KEY WORDS:
Current
Frequency
Oscilloscope
Circuit breaker
ASSESSMENT: