Download What you will need to remember from year 10…

Energy and Electricity
Basic ideas…
Electric current is when electrons start to flow around a
circuit. We use an _________ to measure it and it is
measured in ____.
Potential difference (also called _______) is
how big the push on the electrons is. We use a
________ to measure it and it is measured in
______, a unit named after Volta.
Resistance is anything that resists an electric current. It is
measured in _____.
Words: volts, amps, ohms, voltage, ammeter, voltmeter
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
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…
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
Summary
In a SERIES circuit:
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
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
Resistance
Resistance is anything that will
RESIST a current. It is measured
in Ohms, a unit named after me.
Georg Simon Ohm
1789-1854
The resistance of a component can be
calculated using Ohm’s Law:
Resistance
(in )
=
V
Voltage (in V)
Current (in A)
I
R
An example question:
Ammeter
reads 2A
A
V
Voltmeter
reads 10V
1) What is the resistance across
this bulb?
2) Assuming all the bulbs are the
same what is the total resistance
in this circuit?
More examples…
3A
6V
12V
3A
2A
4V
2V
1A
What is the
resistance of
these bulbs?
Two simple components:
1) Light dependant
resistor – resistance
DECREASES when light
intensity INCREASES
Resistance
2) Thermistor –
resistance DECREASES
when temperature
INCREASES
Resistance
Amount of light
Temperature
Current-voltage graphs
I
I
I
V
V
V
1. Resistor
Current
increases in
proportion
to voltage
2. Bulb
As voltage increases
the bulb gets hotter
and resistance
increases
3. Diode
A diode only
lets current go
in one direction
DC and AC
+
DC stands for “Direct
Current” – the current only
flows in one direction:
V
Time
-
AC stands for “Alternating
Current” – the current
changes direction 50 times
every second (frequency =
50Hz)
1/50th s
+
240V
T
-
V
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, damage, safety, melt, live, circuit, fuse
Other safety devices…
1) Insulation and double insulation
Insulating a wire prevents someone from touching
the ____ wire.
A device can also be double insulated – this is when
the metal parts inside the device are insulated from
the outer case.
A double insulated device does not need an _______
wire but they still have _____.
2) Residual Current Circuit Breaker
This circuit breaker detects any difference in
current between the live and neutral connectors and
switches off the current when needed. They can be
easily _______.
Words – earth, reset, live, fuses
The Cost of Electricity
Electricity is measured in units called “kilowatt hours” (kWh).
For example…
A 3kW fire left on for 1 hour uses 3kWh of energy
A 1kW toaster left on for 2 hours uses 2kWh
•A 0.5kW Vacuum Cleaner left on for 4 hours
uses __kWh
•A 200W TV left on for 5 hours uses __kWh
•A 2kW kettle left on for 15 minutes uses __kWh
The Cost of Electricity
To work out how much a device costs we do the following:
Cost of electricity = Power (kW) x time (h) x cost per kWh (p)
For example, if electricity costs 8baht per unit calculate the
cost of the following…
1) A 2kW fire left on for 3 hours
48B
2) A 0.2kW TV left on for 5 hours
8B
3) A 0.1kW light bulb left on for 10 hours
8B
4) A 0.5kW hoover left on for 1 hour
4B