Additional Science P2.3 Electricity

P2.3 Currents in electrical circuits
The current in an electric circuit depends on the
resistance of the components and the supply.
You should be able to:
■ apply the principles of basic electrical circuits to practical
situations
■ evaluate the use of different forms of lighting, in terms of
cost and energy efficiency.

P2.3.1 Static electricity
Static electricity
Electrons
Repel
Attract
Electric charge

P2.3.1 Static electricity
a) When certain insulating materials are rubbed against each
other they become electrically charged. Negatively charged
electrons are rubbed off one material and onto the other.
b) The material that gains electrons becomes negatively
charged. The material that loses electrons is left with an
equal positive charge.

c) When two electrically charged objects are
brought together they exert a force on each
other.
d) Two objects that carry the same type of
charge repel. Two objects that carry different
types of charge attract.

e) Electrical charges can move easily through some
substances, eg metals. The flow of electric charges is
called current electricity.

Key words
Current
Resistance
Components
Energy efficiency
Static electricity
Electrons
Repel
Attract
Electric charge
Potential difference
Voltage
Work done
Energy transferred
Coulomb
Switch
Lamp
Fuse
Ammeter
Resistor
Thermistor
Variable resistor
LDR
LED
Resistance
Filament bulb
Diode
Cells
Batteries
Earth
Live wire
Neutral wire
Electrical charge
Resistor

P2.3 Electrical circuits:
Series and parallel
circuits

Current
Resistance
Components
Potential difference
Voltage
Coulomb
Switch
Lamp
Fuse
Ammeter
Resistor
Resistance
Cells
Batteries
http://www.teachitscience.co.uk/shared/free/CircuitBuilder_iframe.html
Key words

CURRENT ISSUES
A battery is connected to a bulb. The bulb is glowing.
Which of the four diagrams A - D in your opinion best
describes the electric current in the wires?

A. There will be no electric current The electric current will be in a
in the wire attached to the base direction towards the bulb in
of the battery. both wires.
The direction of the current will The direction of the electric current
be as shown. The current will will be as shown. The current will
be less in the return wire be the same in both wires.
Give a reason for your answer:

http://www.teachitscience.co.uk/shared/free/CircuitBuilder_iframe.html

R1 R2
Resistance matters
A battery is connected to a bulb and two variable
resistors, as above. The bulb is glowing
What happens to the
bulb if ….
R1 increase/
decrease?
R2 increase/
decrease?

I is the current in amperes (A)
Q is the charge in coulombs (C)
t is the time in seconds (s)
a) Electric current is a flow of electric charge.
The size of the electric current is the rate of flow
of electric charge. The size of the current is
given by the equation:
I =
Q
t
A coulomb is 6.2 x 1018 electrons. As the electrons flow
around the circuit they do not get used up.
An amp is a 1 Coulomb per second.

b) The potential difference (voltage) between two points in an
electric circuit is the work done (energy transferred) per coulomb
of charge that passes between the points
V =
W
Q
V is the potential difference in volts (V)
W is the work done (energy transferred) in joules (J)
Q is the charge in coulombs (C)

A battery is a number of cells joined together. They
supply energy to each coulomb as they flow around
the circuit. The energy is transferred from the battery
(chemical potential energy) to the components in the
circuit eg a lamp (light and heat energy).
Batteries are measured in volts. Voltage is the push
given to the electrons as they flow, it is often called
potential difference (pd). A volt is a joule per Coulomb.

Voltage (V)(or potential difference)
is how much energy the charge is
given by the power supply.
Voltage = PUSH
Current (A) is how much charge
flows in the circuit in a certain
time.
Current = FLOW
Resistance (Ω) is how hard it is for the current to flow
Resistance = TRYING TO STOP

What are these?
What job does each
one do in a circuit?

BTEOTSSSBAT:
Identify series circuits
Identify parallel circuits
Investigate how current flows through series and parallel
circuits
Investigate how voltage flows through series and parallel
circuits

What do we use to measure a current?
What do we use to measure a potential difference (voltage) across a component?
ammeter
voltmeter
digital multimeter

Series circuits
What happens to
the current as
more components
are added?

Series circuits
What happens to
the voltage as
more components
are added?

Series circuit
CURRENT:
The current is always the same at each point in the circuit.
VOLTAGE:
The voltage differs over each component - but the total over each
component will add up to the total provided by the battery

Parallel circuits
What happens to the current as more
branches are added?

Parallel circuits
What happens to the voltage as more
branches are added?

Parallel circuit
CURRENT
It splits up - but current in = current out
VOLTAGE
Is the same over each parallel component. It is the
same as the voltage of the battery.

Extension:
Series and parallel circuits

BTEOTSSSBAT:
Know the relationship between current, voltage and
resistance
Solve problems using Ohm's law
Identify electrical safety problems
Wire a three-pin plug correctly

What are the variables?
Independent
Dependent
Controlled
What are the main sources of error?
How can it be minimised?
What is the main health and safety issue?
How can it be minimised?

Match the brightness of the bulbs
Which is the brightest?
Which is the dimmest?

1. What current will flow through a 20Ω resistor with a voltage of 6V across
it?
V = 6V R = 20Ω
so C = V/R = 6/20 = 0.3A
2. What voltage is needed to make 0.5A flow through a 100Ω resistor?
3. A current of 0.23A flows through a bulb when a voltage of 20V is across it. What is its
resistance?

What components would produce these graphs?

What voltage would you get from these combinations?

True or false?
The current through each resistor is the same
The voltage across each resistor is the same
The total resistance is 150Ω
Calculate the current through each resistor
How are these 2 resistors arranged?

True or false?
The current through each resistor is the same
The voltage across each resistor is the same
The total resistance is 150Ω
How are these 2 resistors arranged?
What will the voltage be across each resistor?

This is an LDR. Its resistance gets ……………..
when light falls on it.
This is a ……………….
Its resistance depends on which way round it is
connected
This is a thermistor. Its resistance gets bigger when it
gets …………….
This is a filament lamp. Its resistance gets bigger
when it gets ……………..

1. How much heat energy does a 3kW kettle
produce in 2 minutes?
P = 3,000W t = 120s
So E.T. = P x t = 3,600,000J
2. An electric fire produces 500,000J of heat energy in 3 minutes. Calculate its power.
3. How long will it take a 2kW water heater to give 300,000J of heat energy to the water inside it?

1. A current of 0.5A flows through a 240V
bulb. Calculate its power.
C = 0.5A V = 240V
P = V x C = 240 x 0.5 = 120W
2. What current flows through a 60W, 240V bedside lamp?
3. Which of these fuses should be used inside its plug?
1A 5A 10A 15A 30A

Q1 contd.
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Q2 mark scheme
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Q2 Foundation AQA-PH2FP-QP-Jun12 Q4
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Q2 contd.
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Q2 mark scheme contd.
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Q3 Higher AQA-PH2HP-QP-Jun12 Q5
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Q3 contd.
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Q3 mark scheme
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Q3 mark scheme contd.
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Additional Science P2.3 Electricity

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