Introducing
Your new presentation assistant.
Refine, enhance, and tailor your content, source relevant images, and edit visuals quicker than ever before.
Trending searches
TEKNİKİNG SUNUM
9
Static and current electricity
hypothesis
INTRODUCTION
When two different substances rub together,
electrons are transferred from one substance to
the other. One substance gains electrons and
becomes negatively charged. The other loses
electrons and becomes positively charged.
However, this happens only with certain
substances, such as polythene, acetate, wool,
and rubber. Other substances that can be
charged in this way include glass, ceramics,
nylon, paper, and air. These substances are
known as insulators. The electrons stay fixed
on the surface of the substance and can not
move away. Insulators do not let charge flow
through them. We say the charge is static, a
word meaning ‘standing’.
A person may become charged when walking
on a carpeted floor. The rubbing of their plastic
soles against the carpet (often nylon) generates
a charge on the person. In very dry climates the
charge on the person may become very large.
They feel a ‘tingle’, hear a tiny ‘tick’ or may
even see a spark, when they touch an earthed
metal object, such as a door handle.
Similarly, just sitting working at a desk may
generate charge because of the person’s
woollen, nylon or polyester clothes rubbing
together. Electronics engineers have to be
particularly careful to avoid this, as the charge
they pick up on their bodies may destroy
delicate electronic components when they
touch them.
hypothesis
LIGHTNING
The charges build
up so much that
there is a strong
attraction between
the electrons and the
nearest positive
charges. A lightning
flash occurs as
electrons rush across
the gap. The air
along the flash is
heated so much that
it causes a shock
wave, which we
hear as thunder.
Small particles in a cloud collide together. It
is thought that the larger particles gain
electrons and become negatively charged.
The smaller particles lose electrons and
become positively charged. Movements in the
cloud tend to sort out the particles by size.
The top of the cloud has a positive charge,
and the bottom a negative charge.
discussion
Most lightning flashes are within a cloud,
and some are between a cloud and one of its
neighbours. They do not do any damage,
except possibly to aeroplanes flying through
the cloud.
The most dangerous flashes are between a
cloud and charged areas on the ground.
discussion
discussion
Some substances let electric charge flow
through them. These substances are called
conductors.
One of the best-known conductors is copper. It
conducts so well because the electrons of
copper atoms are able to escape easily from the
atoms.
CONDUCTORS
experiment
In a piece of copper, the atoms (large spheres in
the drawing above) are arranged in regular
rows and columns, called a lattice. The
electrons that have escaped from the atoms
(small circles) are able to wander about freely
in the space between the copper atoms.
If we connect a battery to each end of a strip of
copper, its negative terminal supplies electrons
to the copper. Its positive terminal removes
electrons from the other end. They are attracted
by the positive (opposite) charge.
experiment
e l e c t r i c
The flow of
electrons along
the copper strip
is called an
e l e c t r i c
current. The
flow is from
negative to
positive.
Thing to do test different substances to find out if they
are conductors or insulators (nonconductors).
What Happened
Try this with different materials, such as:
an iron nail or screw (as shown), a piece of
brick, a copper strip or wire, a plastic rod, a
strip of aluminium kitchen foil, a piece of
wood, a ‘silver’ coin, the ‘lead’ of a pencil
(not really lead, but carbon), a piece of
stone, and other materials..
The lamp shines when the material is a
conductor. Make lists of conductors and
non-conductors.
Matter is made up of molecules of many
different kinds. Molecules are made up of one
or more atoms. Atoms are made up of electrons
(negatively charged), protons (positively
charged) and neutrons (uncharged).
Electrons and atoms
The simplest possible atom consists of one
electron and one proton. The proton is at the
centre of the atom and the electron is circling
around it, in orbit.
:)
:(
Each element has its own distinctive structure,
the atoms being made up of fixed numbers of
electrons and protons.
In spite of these differences, all elements have
the same basic plan. There is a central part,
called the nucleus, where most of the mass of
the atom is concentrated. The nucleus is
surrounded by a cloud of circling electrons.
Atoms other than hydrogen have more than
one proton and also some neutrons in the
nucleus.
;)
With one unit of negative charge on the
electron and one unit of opposite but equal
charge on the proton, the atom as a whole is
uncharged.The electron is circling at high speed around
the proton, like a planet orbiting the Sun. There
must be a force to keep it in orbit. In the case of
a planet the force is gravity, the attraction
between the masses of the Sun and the planet.
In the case of the electron the force is the
electrical attraction between oppositely
charged bodies. The experiments on pages 2-3
demonstrated this.
;(
The protons in the nucleus give the nucleus a
positive charge — one unit of charge for each
proton. The number of electrons in the cloud
equals the number of protons, so the cloud as a
whole has an equal but negative charge which
balances the charge on the nucleus.
The electrons of an atom are on the outside.
They can be removed by friction, heating and
electric fields. This is how we obtain the supply
of electrons to use in the electronic circuits and
devices described in this book.
Other kinds of atom
other kind of atoms and particles
There are more than a hundred different
elements in nature, including hydrogen,
helium, copper, zinc, iron, mercury and
oxygen, to name only a few.
Other particles
Some readers may have heard of quarks and
other sub-atomic particles. Detailed studies by
atomic scientists have discovered that atoms
are actually made up of several more sorts of
particle. In electronics, however, the only
particle we need to know about is the electron.
Which of these represent ions?
Cl–, CuSO4, Na+, H2O,
SO4--
, H2, NaCl.
question
CL- , NA+
ANSWER
QUESTION
List these substances in order, from the
best conductor to the worst:
aluminium, rubber, copper, carbon, gold,
silver.
silver, copper,gold,
aluminum
ANSWER
RUBBER, CARBON
insulator