Page 143 - How It Works - Book of Amazing Answers To Curious Questions, 12

Technology ' Q�

________________

Why do I need
an electrical

adaptor abroad?

f you travel to a different country, one of the
I first things you might look for in your hotel
room is a plug socket. Only there is a good
chance it will look different, maybe bigger,
smaller or have a different number of holes.
This is because back when electricity grids
were first being introduced, many countries
decided to develop plugs and sockets of their
own rather than adopting a world standard.
As well as the shapes and sizes of the plug
sockets changing depending on the country, How do the
the voltage and frequency of the AC current
varies too. For example Europe and most streetlights
other countries in the world use
a voltage which is
twice that in tum on
the US. Plug
an appliance automatically?
from the US
into a power T he most commonly used component in
supply in streetlights is called a cadmium sulphide
Europe without photoresistor, or a CdS cell for short. The CdS
an adaptor and cell changes the resistance of a circuit
you will probably depending on the amount of light shining on
see a spectacular it. When lots of light falls on a CdS cell, then
yet highly the resistance is very low, which means it
dangerous firework conducts electricity well. When there is not
display as the voltage will Why do the fuses much light, the photo-resistor has a high
be too high. It is worthwhile to check the resistance which means not much current
power outlets of the country you are visiting sometimes Elow can flow.
before you travel, then you can make sure you This change in current can then be used to
in my house? electromagnetic switch; when the
take the correct adaptor. control a relay. A relay is basically an
electromagnet has a high current (lots of light
Who invented W being drawn from a plug socket is falling on the photo-resistor - daytime) then it
hen a certain amount of current
pushes the switch open so no current can flow
the mobile exceeded, the fuse is designed to 'blow' to to the streetlight. When it gets dark, then not
much current can flow to the electromagnet
protect the wiring in the house and the
phone? appliances connected to that specific circuit. so the switch closes and allows electricity to
flow to the streetlight, turning it on.
Electricians install fuses as a safety feature so
that a large surge in power does not cause an
T he invention of the first handheld mobile electrical fire. A fuse is simply a small wire
phone is credited to Dr Martin Cooper running from one electrode to another '' The cadmium
and his team at Motorola in April 1973. The electrode and encapsulated in some kind of
first call he made was to his rival inventor, Joel fire-proof casing. sulphide photoresistor
Engel at Bell Laboratories, who had also been An appliance that needs more power than a
racing to invent the first mobile phone. Before fuse can supply will ultimately blow the fuse. cell changes the
this time, radiophones on-board ships and in Most houses use circuit breakers that operate
cars were available; however, Dr Cooper's by similar means, although these differ from resistance of a circuit
phone was the first truly handheld modern fuses in that they can be reset. If too many
mobile phone. It weighed in at around two appliances try to draw power from a wiring depending on the
kilograms and had a battery life of only 20 system at once, switching on a new appliance
minutes. According to Cooper, this didn't can 'trip' the circuit breaker and cut power, amount of light
matter as you couldn't really hold the phone which is why switching on an appliance such
up for that long! as a light can cut the power in a house. shining on it ''

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