Page 12 - Physics_Form_2

Physics for Secondary Schools

net negative charge, while the electrons missing from the wool lead to a net positive
charge. The combined total charge of the two objects remains the same. Charging is
conserved, which means that individual charges are neither created nor destroyed. All
that happened was that the positive and negative charges were separated through the
transfer of electrons.

Hard rubber rod
FOR ONLINE READING ONLY

Wool

(a) (b)

Figure 1.6: Separation of charges
Law of conservation of charge Electrostatic force

A charge is a characteristic of matter that The interaction between static electric
causes it to create and experience electrical charges produces a force known as the
and magnetic effects. The underlying idea electrostatic force. For instance, when
behind charge conservation is that the plastic rods are charged by rubbing them
system’s overall charge is conserved. It with fur, they repel each other. Similarly,
can be defined as follows: glass rods rubbed with silk also become
charged and repel one another. Additionally,
According to the rule of conservation plastic rods attract the fur, while glass rods
of charge, the total charge of an attract the silk.
isolated system will always remain
constant. At any time intervals, any French physicist Charles Coulomb measured
system that is not exchanging mass or the force between two charged objects using
energy with its surroundings will have a torsional balance, establishing a unit of
the same total charge. electrical charge named the coulomb in
his honour. A coulomb is a much larger
quantity of charge than that normally
When two objects in an isolated system produced by rubbing.
each have a net charge of zero, and one
body transfers one million electrons Activity 1.2
to the other, the object with the surplus
electrons will be negatively charged, Aim: To demonstrate the
while the object with fewer electrons existence of the
will have a positive charge of the same electrostatic force
magnitude. The total charge of the system Materials: plastic pen, plastic comb,
has never changed and will never change. tissue paper, human hair

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Student’s Book Form Two

Physics Form 2 Final.indd 6 25/10/2025 10:25