Power House
What to do: Press buttons to switch on appliances in the house.
What happens: The meters show how much power the appliances
require and how much it costs.
HOW IT WORKS
1. The doll's house has lots of model
appliances; TV, fridge, washing machine,
lights, etc. which can be switched on.
None of the models actually works,
but little lights come on and the
electricity meter operates as
though they are real appliances.
2. When you press the electric kettle button, for example, the electric
meter counts in the same way that a real meter would if a real kettle
had been switched on. If you switch on more appliances, the meter
shows the total rate of energy use.
meter
plug and
socket
power station
3. As you might have guessed, a computer inside the exhibit mimics the
way that different electrical appliances use electrical energy.
So you can tell from the meter which ones use a lot of energy
and which are more modest users.
The meter also produces information about
the cost of this energy. The right hand
display panel shows how many joules of
energy have been used since switching on.
appliance
computer
in the loft!
joules
The other display shows either the cost per
hour or the quarterly cost of operating the
appliances (three months, with eight hours' use
per day) . You have to operate a switch to
choose between these two costs.
£
p
4. If you have tried various appliances on the exhibit you will have
noticed that the ones requiring most power are those which produce
a lot of heat - electric kettle, washing machine, electric radiator,
tumble dryer, etc.
DID YOU KNOW?
magnetic
current coil
brake
rotor
voltage
coils
meter
• Many domestic electricity meters still use a little electric motor which
turns at a speed which depends on the rate at which energy is being
used "downstream" of the meter. If you are using a lot of energy, the
electric current flowing through the meter is larger, so it turns faster.
The motor turns a series of cogwheels connected to a sort of
mileometer which measures energy in kilowatt hours. The meter in this
exhibit has electronic counters and display units instead of
mechanical ones.
• Electricity provides "high grade" energy which you can use
immediately for running electric motors and electronic equipment.
Gas, oil, coal, etc. only provide "low grade" energy, i.e. heat,
when you burn them. They go to a lot of trouble in power stations to
convert heat into electricity, so using electricity to produce heat again
(in electric fires or storage heaters) is much more expensive than
burning the fuel yourself.
• You buy electrical energy by the "unit",which is the energy needed to
keep a one kilowatt electric fire going for one hour. This unit, the
kilowatt hour, is 3,600,000 joules of energy and costs about 8p on
the ordinary tariff (1996).
• Real electrical appliances - cookers, lights, freezers, washing machines, etc. require different
amounts of energy every second so that they will work. For example, a light bulb might need
60 joules per second (i.e. 60 watt); an electric kettle may require 2000 joules per second
(2 kilowatt), etc. The required energy supply rate (or power) is usually stated on the appliance.
The power limit for a fit man working continuously is about 200 joules per second, so it would
need 10 fit men working hard and turning a generator to run an electric kettle.
One horse power is about 750 joules per second, so it would need three horses!
• The names of the various measurement units
commemorate famous scientists and
engineers. James Joule was a famous
Victorian scientist; James Watt vastly
improved the steam engine and invented the
"horse power" unit. Instead of horse power,
most car makers now say how many
kilowatts their engines can provide.
• You can easily work out how strong an electric current will flow to
provide the power needed by an appliance. For 1 kilowatt, the
current is 4 amps, for 2 kilowatt it will be 8 amps, etc. The fuse to put
in the plug must melt when this current is exceeded, because
something is wrong. For 1 kilowatt, use a 5 amp fuse; for three
kilowatt, use a 13 amp fuse.
THINGS YOU CAN TRY YOURSELF.
•
STUART STREET
CARDIFF
CF10 5BW
Watch the electricity meter at home. Compare the rate at which the motor goes
round when there is only the odd light on and when there is an electric fire,
a water heater or a shower (or even all three) switched on. The fright you get will
probably encourage you to switch things off when you don't really need them!
T 029 20 475 475
F 029 20 482 517
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