Additional Material
LIGHT AND ELECTRICITY
In
some types of electric lamp, light is given off from a length of wire
known as a filament. It is necessary to know something about electricity in
order to understand why an electric filament gives off light.
An
electric current is the movement of very small particles called electrons along
a wire. These electrons have negative charges. Normally they orbit the
positively charged nucleus of an atom. Normally the number of electrons is
equal to the number of positive charges in the nucleus. Atoms are so small that
a million of them could fit across the thickness of a sheet of paper.
Everything
is made up of atoms. In a metal some of the electrons break free from the atoms
and move about on their own between the atoms. Electrons that do this are known
as free electrons. If a metal wire is connected to a battery, the voltage of
the battery makes the free electrons move away from the negative electrode and
towards the positive electrode. This is because a negative charge is attracted
towards a positive charge and repelled from a negative charge. The
greater the voltage of the battery, the faster the electrons move and the
greater is the current. Electric current always flows as a result of a voltage.
As
the electrons move through the metal some of them collide with the atoms that
make up the metal. As the current increases the collisions become more and more
violent and the atoms begin to vibrate backwards and forwards faster and
faster. The temperature of the wire is a measure of the speed of movement of
these vibrating atoms. As the current goes up the wire gets hotter and hotter.
When an electron collides with a vibrating atom, the electron may slow
down or stop. Electrons have electric fields around them since they have an
electric charge. When they slow down a magnetic field is produced in such a way
that electromagnetic waves are given off .Sometimes an electron collides
with a vibrating atom in such a way that the electron speeds up. Again
electromagnetic waves are given off Most of the electromagnetic waves
produced are infra-red, some are waves of visible light and, when the metal
becomes very hot, a few are ultra-violet.
GEORGE
K. STONE Science in Action
Vocabulary
Given off : memancarkan
Fit across : melalui
Volt :
unit daya listrik
Repelled : menarik atau melempar
Vibrating : bergetar
Filament : kawat pijar pada bola lampu
Exercise
1: Answers and Reasons
Answer the following questions.
1.
What is electric current?
2.
What is a filament?
3.
How big is the atom?
4.
What are free electrons?
5.
What happens when free electrons flow through a metal wire?
6.
Why does the wire get hotter as the current gets stronger?
7.
What is the correlation between a voltage and an electron
movement?
8.
What happens when an electron collides with a vibrating
atom?
9.
Why does an electron has electric fields?
Exercise 2: True or False
Now decide if these statements are true
or not true
1.
An electric current is a flow of footballs.
2.
Conductors allow a current to pass easily.
3.
Acids, gases and salts are insulators.
4.
Insulators allow some current to pass through.
5.
Electric wires don't need insulating.
6.
An electric current is something moving.
7.
An electric current flows from the positive to the negative
terminal.
Exercise
3: Advantages and Disadvantages
What are the advantages and
disadvantages of using 110 voltages and 220 voltages? Write it in one
paragraph, and then present it orally in front of the class.
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