Page 146 - Science Coursebook

10.3 Electrons on the move

It is easier to understand how something
becomes electrically charged if we can picture electron – negative
the particles of which it is made.

All substances are made of atoms. If you have nucleus – positive
studied Unit 4, you will know that every atom
has a tiny nucleus at its centre. Electrons orbit
around the nucleus.
The nucleus has a positive electric charge. Atoms are made up of charged particles. This shows the
The electrons have negative electric charge. positive and negative particles in an atom of lithium.

Questions

1 An atom is usually described as ‘neutral’. What does this tell you about the
amounts of positive and negative charge in an atom?
A+I 2 The nucleus of an atom attracts the electrons which orbit around it. This is
what stops an atom from falling apart. Explain why the nucleus and electrons
attract each other.

Explaining static electricity
When an acrylic rod is rubbed with a cloth, it becomes positively
charged. What is going on?
The cloth rubs against the atoms which make up the surface of
the rod. The force of friction rubs electrons from these atoms
onto the cloth.
Because the cloth has gained negatively charged electrons, it
now has a negative charge.
The rod is no longer neutral. It has lost electrons, so it has a
positive charge.

Why do electrons move from the rod to the cloth? The reason
is that the electrons are on the outside of the atoms, so they are Rubbing transfers electrons
easily transferred from one material to the other. from the rod to the cloth.

Some materials hold on to their electrons more strongly than
others. Acrylic holds its electrons weakly, so it easily loses them
and becomes positively charged. Polythene holds its electrons
more strongly.

Question
A+I 3 Use the same ideas to explain why a polythene rod gains a negative charge
when it is rubbed with a cloth.

144 10 Electricity

A+E SE