• Be able to describe and explain the difference
between DC and AC current.
• Be able to describe the colours and purpose of Live,
Neutral and Earth wires.
• Understand why insulation is important
for mains voltage.
Task 1 - Recap
Remind the person next to
you:
• How the resistance of a
bulb changes with temperature, and why this happens.
• How the resistance of a
thermistor changes with temperature, and why this happens.
• How the resistance of an
LDR changes with light intensity, and why this happens.
• The difference between DC
and AC current. You met these in our work on the national grid in
year 10!
Task 2
Mains electricity uses AC
current, and is slightly different to the DC current which flows in the
circuits we have built so far. Your teacher will explain the
difference between AC and DC current using the simulation below.
Click to Run
Teacher note: there is a local copy stored
here if the phet website is inaccessible.
Task 3
Write the title "Mains
Electricity" in your exercise book. Your teacher
will give you a copy of the text below.
There are two types of electrical
____________. The first is DC, which stands for ____________
current. This is the type of current that flows from a battery
or cell, and is most familiar to us. The direction of flow of
the charges is always __________________.
The second type of current is AC, which stands
for ________________ current. In this type of current the
direction of flow of the charges is constantly _______________.
UK mains electricity is AC, and it changes direction ______
times per second. We say that it has a ______________ of 50Hz.
Mains electricity is also a much higher
_____________ than is produced by most cells or batteries. This
can make it very dangerous. The cables have to be covered with
plastic _____________ to prevent users being harmed.
Fill in the missing words and
stick the sheet into your exercise book. When you have finished,
your teacher will check your answers.
Task 4
Another important difference
with mains electricity is the high voltage (230V), which can present
considerable danger to the user if there is a fault. This
necessitates a third wire in many appliances. You need to know the
colours of each wire in the plug, and where they are connected.
Your teacher will give you a plug, like the one below, to take apart.
Strip the plug down into the
separate component parts, and then try to put it back together again.
When you have finished, show your teacher before putting
the case back together.
SAFETY:
Your plug has a rivet through one of the pins to
prevent you from plugging it in, but even so you MUST NOT
attempt to plug your plug into a mains socket.
Your teacher will give you a
diagram, like the one below, and some colouring pencils. Show the
colour of the insulation on each wire, and give each part of the plug a
suitable label.
Teacher note: need to create link to
digital copy of diagrams!
Task 5
Were you correct? Find
out, by helping your teacher to correctly label the parts of the plug on
the diagram below.
Homework/Extension
Lots of different materials
are used in the construction of a plug.
This sheet lists some of the materials which are commonly used, with
the characteristics that makes them useful. Match each material to
the correct description and stick them into your exercise book.
Make sure your work is
labelled "Gwaith Cartref" and has a date.