SNC1D1: Notes
Law Of Attraction And Repulsion
 LIKE CHARGES REPEL AND OPPOSITE CHARGES ATTRACT
 Note: The devise used to detect charges is an electroscope
 Conductors allow electrons to flow easily through them; therefore they are
excellent conductors of electricity.
e.g. Metals are excellent conductors – silver, copper, gold, aluminum, etc
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 Insulators do not allow electrons to flow through them easily; therefore they
are poor conductors of electricity.
e.g. Non-metallic objects tend to be poor conductors – glass, rubber, plastic,
cotton, wood, etc
Note: A charged object can be discharged by simply touching it. In these cases
the excess electrons travel from the conductor through your body to the
Earth.
 The process of conducting a charge to or from the Earth is called
grounding and is symbolized by the symbol outlined below.

All particles can have one of two possible charges
a) Negative
b) Positive

However there are three possible charged states
1) Negative
2) Positive
3) Neutral
 Remember that atoms are composed of protons, neutrons and electrons,
and that in nature most atoms exist in a neutral (uncharged) state.
 Protons have a positive charge
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 Electrons have a negative charge
 Neutrons have a neutral charge
 Any atom that possess an excess or deficient amount of electrons are called
ions
NOTE: Protons and Neutron DO NOT move, only electrons have the ability to move
(come and go)
 A positively charged atom or material has a deficient number of electrons
in comparison to the number of protons. In other words there are more
protons present than electrons, therefore the atom or object has a
positive charge
 A positively charged atom is called a cation
 A negatively charged atom or object has an excess number of electrons in
comparison to the number of protons. In other words there are more
electrons present than protons, therefore the atom or object has a
negative charge.
 A negatively charged atom is called an anion.
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WHAT IS THE RELATIONSHIP BETWEEN CHARGED & NEUTRAL
OBJECTS
(A)
Neutral Object – Paper
(B) Negatively Charged Object
– Comb
Charges are evenly distributed
Charges are unevenly
distributed
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(C)
Electrons in the paper shift
(D) Attractive forces
between the
slightly away from the comb
protons and the electrons are
greater than the repulsion forces
between the electrons in both objects
HOW DO OBJECTS BECOME CHARGED
 There are three methods of charging
1) Charging by Friction
2) Charging by Contact
3) Charging by Induction
1. Charging by Friction overview – Charging by friction occurs when two different
neutral materials are rubbed together. There is a transfer of electrons from
one object to another, thereby causing one object to become negatively
charged and the other positively charged. In charging by friction the two
objects being charged receive opposite charges.
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2. Charging by Contact overview – Charging by contact occurs when the object to
be charged is brought in contact with a charged object such as a charged rod.
The neutral object (the object being charged) becomes charged after contact is
made with the charged object. The object being charged receives the same
charge as the charging agent. In this process there is a transfer of electrons
to or from the charging agent when contact is made.
3. Charging by Induction overview – Charging by induction occurs when a charged
object such as a charged rod is brought near but does not come in contact
with the neutral object or object being charged. In charging by induction,
electrons are induced to or from the object being charged. In this process the
object being charged receives a opposite charge in comparison to the charging
agent.
Examples:
1. Charging By Friction – When two different neutral materials such as fur and
ebonite rod are rubbed together, both objects become charged. The
ebonite receives a negative charge and the fur receives a positive charge.
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2. Charging by Contact – When charging by contact, a charged object is used
to charge a neutral object by bringing the neutral object in contact with
the charged one. The neutral object receives the same charge as the
charging agent.
(A)
Neutral Electroscope
(B) Positively charged
acetate is
brought in contact with the
electroscope allowing some
electrons to transfer from the
electroscope to the acetate.
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(C) The acetate is removed and the electroscope is left with a positive charge
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3. Charging by Induction. When charging by induction, the charging agent does
not come in contact with the object being charged. Electrons are induced
to or from the object being charged. The object being charged receives an
opposite charge in comparison to the charging agent.
Note: positive charging agents will produce negatively charged objects and
negative charging agents will produce positive charged objects.
A) Neutral Electroscope
B) Negatively charged object is
C) Electroscope is
grounded
brought close but not
touching
allowing some electrons
the electroscope. The
electrons
to be transfer to the ground
are repelled to the leaves of
the
by the grounding agent.
electroscope. The leaves
move
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apart because like charges
repel.
D) Grounding agent removed
E) Negatively charged
agent removed
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