19168_FOMT_1_073-084.qxd
C
20.5.2008
8:44 Uhr
Seite 82
Focus on technology
WHAT IS “ELECTRICITY”?
A
ll material consists of atoms. Atoms are
made up of three particles: electrons, protons and neutrons. The electrons orbit a
central core or nucleus, which is made up of
protons and neutrons.
There are two ways of doing this, one by using a
magnetic field and the other by using a chemical
reaction.
Electrons have a negative charge (–) and protons
have a positive charge (+). The charges are equal
but opposite. Similar charges repel each other and
opposite charges attract each other. These natural
forces of repulsion and attraction are harnessed to
generate electricity.
There is, however, a problem. In an atom, the
electrons orbit the nucleus at random (regellos). In
this state, electricity does not flow.
But when a majority of electrons move in the same
direction, they generate a current. This property
means that to generate electricity, it is necessary
to find a way of making electrons move in the
same direction.
82
If a coil of wire is rotated between the positive and
negative poles of a magnet, the electrons in the
wire move around the coil in the same direction.
This happens, too, if a permanent magnet inside a
coil of wire is rotated, as in a dynamo.
A chemical reaction can also be used to separate
electrons from their atoms. Free electrons then
move from one pole to the other. In inexpensive
AA, C or D dry cell batteries (normal flashlight
batteries), the ends of the battery are the
terminals. In a large car battery, there are two
heavy lead posts that act as the terminals.
Electrons collect on the negative terminal (the
anode) of the battery. If you connect a wire
between the negative and positive terminals, the
electrons will flow from the negative to the
positive terminal (the cathode) as fast as they can
- and exhaust the battery very quickly, so don’t do
it. Normally, you connect some type of load to the
battery, a light bulb, say, or an electronic circuit in
a cellphone.
19168_FOMT_1_073-084.qxd
20.5.2008
8:44 Uhr
Seite 83
UNIT 5
1
KEEPING IN TOUCH
Tick (✓) a box to say if these statements are true (T) or false (F). Correct the false
statements.
T
F
1 Atoms are made up of electrons, protons and neutrons.
2 The central core of an atom is called the ‘neutron’.
3 Electrons have a positive charge, protons a negative one.
4 Charges of the same type repel and opposites attract.
5 Electrons move around the nucleus in the same direction.
6 Current can flow only when electrons move at random.
7 A magnetic field or a chemical reaction can free electrons.
8 Dynamos are a permanent magnet rotating inside a coil.
9 In batteries, free electrons flow from one pole to the other.
10 The negative pole of a battery is the cathode.
Corrections:
_____________________________________________________________________________
_____________________________________________________________________________
_____________________________________________________________________________
_____________________________________________________________________________
_____________________________________________________________________________
2
Complete the sentences with words from the text.
1 Atoms consist of three ________________: electrons, _______________ and neutrons.
2 The _________________ of an atom consists of protons and ____________________.
3 We _____________ electricity by harnessing the natural ____________ within atoms.
4 The problem is that electrons _____________ the nucleus _____________________.
5 Current can only ___________________ if most electrons are moving in the
same ________________.
6 A _______________ field or a _________________ reaction is used to free electrons.
7 In _____________________, a magnet is __________________ within a coil of wire.
8 In batteries, electrons _______________ on the anode or negative _______________.
3
Match the steps of the instructions with the pictures.
How to make a lemon battery
1 Take a fresh lemon, a copper coin and a galvanised nail.
2 Push the coin into one end of the lemon and the nail into the other end.
(The coin and the nail are the electrodes, the acid juice in the lemon is
the electrolyte, together they form a very weak battery.)
3 Four or more lemon batteries will light an LED lamp.
83