Transcript Electricity in the home - Science at St. Dominics

Physics
Electricity in the
home
What is direct current (d.c.)?
Direct current (d.c.) is an
electric current that always
flows in one direction.
Made by batteries.
Electronic circuits such as
those in computers and
stereos need direct current
electricity in order to work.
Direct current cannot be
transferred well over large
distances.
What is alternating current (a.c.)?
Alternating current (a.c.) is
an electric current that is
constantly changing direction.
produced by most generators
and is used in mains
electricity.
Motors often work using
alternating current. The
voltage of alternating
current is easily changed
with a transformer.
Alternating current can be
transferred efficiently over
large distances.
Which type of current – a.c.
or d.c.?
Electricity supply to our homes
• Voltage of 230 v a.c.
Plugs and electrical cable
An electrical plug is inserted into a socket and the
cable which is attached to the plug carries electricity
to the appliance.
Inside an electrical cable
copper
There are three wires made out
of copper
Each wire is surrounded in
plastic.
insulating plastic
Materials in a plug
The live wire carries a current
from the mains supply to the
applicance . It is brown
The earth wire is a
safety device that
allows current to flow
from the appliance to
the plug if there is a
fault in the appliance. It
is green and yellow!
The neutral wire carries the
current from the appliance to the
mains supply. It is blue
What is a fuse?
A fuse is a safety device
When a large current flows the wire becomes hot.
If too much current flows, the wire overheats and
How
does
a
fuse
work?
melts which breaks the circuit.
terminals
thin wire with
high resistance
case made of
insulating material
How to wire a plug correctly
• Open the plug
• Connect live wire to the
live pin with the fuse on
it
• Connect the neutral wire
to the neutral pin
• Connect the earth wire
to the earth pin!
• Close the plug!
Plugs – true or false?
Power ratings
• Power is the amount of energy used per
unit time.
• Power is measured in watts.
High power rating
• Things that use a lot of power e.g electric
heater, dishwasher
Low power rating
• Appliances that use a small amount of
power E.g CD player 15 W power rating,
computer 70 W
Paying for electricity in Ireland?
• It depends on how many units
of energy used
• Unit of energy used = kilowatt
hour.
• A kilowatt hour =
amount of energy
needed for 1kW of
power to be used for 1
hour.
Cost of electricity
cost = number of kilowatts x number of hours x cost per hour
Buying electricity problem
A kettle has a power rating of 8 kW
It is turned on for 5 hours.
If electricity costs 10 c per kilowatt hour
how much does it cost to use the kettle?
Cost of electricity:
cost = number of kW x number of hrs x cost per hr
= 8kW x 5hrs x 10 c/ kWhr
= 400c or 4 euro
A toaster has a power rating of 6 kW
It is turned on for 3 hours.
If electricity costs 9 c per kilowatt hour how
much does it cost to use the kettle?
Cost of electricity:
cost = number of kW x number of hrs x cost per hr
= 6kW x 3hrs x 9 c/ kWhr
= 162c or 1 euro 62 cent