Transcript Electrical Circuits

Electrical Circuits
Energy transfer in circuits
Energy cannot be created or destroyed.
In all devices and machines, including electric circuits,
energy is transferred from one type to another.
When this circuit is connected, chemical energy stored
in the battery is transferred via electrical energy to heat
and light energy in the bulbs.
The total amount of heat and light energy is the same
as the amount of chemical energy lost from the battery.
Energy transfer in electrical circuits
5 J transferred to bulb
as light energy
chemical energy
from battery
(e.g. 100J)
95 J transferred to
heat energy
of bulb
Most of the energy from the battery does not produce light
– most of it is wasted as heat!
What is the energy transfer?
Batteries can power many electrical devices.
What sort of energy is electrical energy transferred into
in these electrical devices?
What is an electrical circuit?
An electrical circuit is like a central heating system in a house.
 There is a pump
that pushes water
around the system.
 The water
everywhere starts
to move at the
same time.
 There are pipes
that carry the
water.
 In the pipes the
water is flowing.
low
pressure
boiler
and
pump
high
pressure
radiator
radiator
flow of
water
What is an electrical circuit?
The bulb in the circuit is like a radiator. An electrical device
uses electrical energy supplied by the circuit.
Instead of a flow of water, electricity flows in an electrical
circuit.
The wires are like pipes; they carry the flow of electricity
(called current) around the circuit.
The electrical current is pushed by the cell (or battery), which
has the same function as the pump and boiler. The strength of
push provided by the battery is called its voltage.
Drawing Circuits
1) A battery, a
bulb and a switch
‘in series’
2) A battery of
cells, a switch
and two bulbs
in series
Components in an electrical circuit
Measuring current
The unit of measure for current is the amp, which has the
symbol A.
Current is measured using a device called an ammeter.
In a circuit diagram, an ammeter is shown by the symbol A .
When measuring the current through a component, the
ammeter is always connected in series (in the same loop)
with that component.
A
Current in a series circuit
If the current
here is 2
amps…
The current
here will
be…
The current
here will
be…
And the
current here
will be…
In other words, the current in a series
circuit is THE SAME at any point
Changing the current
If a battery is added
the current will
________ because
there is a greater
_____ on the
electrons.
If a bulb is added the
current will _______
because there is
greater ________ in
the circuit
What is a series circuit?
This is a simple series circuit.
In a simple series circuit, everything is
connected in one loop across the terminals
of the battery. So there are not any points
where the current can split or join (these are
called junctions).
This circuit has two lamps connected in series.
Circuits are always drawn using straight lines.
Examples of series circuits
Here are some other simple series circuits:
1. Two resistances (resistors) connected in series:
R1
R2
2. A rheostat (or variable resistor) and a bulb connected
in series:
Series circuits – key ideas
1. In a series circuit the current is the same in all parts
of the circuit.
2. The supply voltage is shared between the components
in a series circuit. (The sum of the voltage across each
component is the same as the total supply voltage.)
3. The current depends on the voltage in any circuit.
Current in a parallel circuit
A parallel circuit is one where the current has a ‘choice of
routes’.
Here comes the current…
Half of the current
will go down here
(assuming the bulbs
are the same)…
And the rest will go
down here…
Current in a parallel circuit
If the current
here is 6
amps
And the
current here
will be…
The current
here will be…
The current
here will be…
The current
here will be…
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.
Comparing series & parallel circuits
Series circuit
Parallel circuit
If one bulb blows they all go
out.
If one bulb blows only that
one goes out.
One switch operates all of
the bulbs.
Each bulb can be turned on
and off with its own switch.
The voltage across the
power supply is shared
between all of the bulbs.
The voltage across each
bulb is the same as across
the power supply.
The current from the power
supply is low.
The current from the power
supply is high.
Measuring voltage
Voltage is measured using a device called a voltmeter.
In a circuit diagram, a voltmeter is given the symbol V .
When measuring the voltage across a component, the
voltmeter is always connected in parallel with (or across)
the component.
V
1
This is still
a series circuit.
V2
V3
The voltage supplied by the battery is shared between all
the components in a series circuit.
Measuring voltage across a
resistance or a bulb
Voltage is measured by connecting the voltmeter
across (or in parallel with) the component.
V
Voltage is measured in volts and the symbol for this is V.
A
Components
component
here
V
R
Wiring a plug
Earth wire
Live wire
Fuse
Neutral wire
Insulation
Cable grip
Fuses
Fuses are _______ devices. If
there is a fault in an appliance
which causes the ____ and
neutral (or earth) wire to cross
then a ______ current will flow
through the _____ and cause it to
_____. This will break the
_______ and protect the
appliance and user from further
_____.
Words – large, harm, safety, melt, live, circuit, fuse
Earth wires
Earth wires are always used if an appliance has a _____ case.
If there is a _____ in the appliance, causing the live wire to
______ the case, the current ‘_______’ down the earth wire
and the ______ blows.
Words – fuse, fault, metal, surges, touch
Circuit breakers
If the current becomes too high the __________ is activated.
This will ______ the iron and the contact will be _______.
This will break the circuit.
Circuit breakers have two main advantages over fuses: they
work ______ and can easily be ______.
Words – electromagnet, broken, attract, reset, quicker
Multiple Choice Quiz