Unit E: Electrical Applications
Chapter 12: Static and Current Electricity
12.1: Electric Charges
pg. 460
Key Concepts:
1. Static electricity is the result of an imbalance of charges
on the surface of an object.
2. Objects can be charged by contact or by induction.
Charges
To understand electric charges, you have to look at the
particles that make up matter, protons, neutrons and
electrons.
Figure 1: A Lithium atom.
Electrons (blue) can move from
atom to atom.
Atomic Structure and Electric Charge
Electric Force: force of attraction or repulsion between
charged objects.
Electric Charge: positive or negative charge on objects that
exert an electric force.
Neutral: having no charge or an equal number of positive
and negative charges.
Neutrons and protons are located within the nucleus of an
atom, electrons are found orbiting the nucleus. Protons and
neutrons are unable to leave the nucleus, but electrons can
be lost or gained, passed from one atom to another.
Protons will repel other protons but are attracted to
oppositely charged electrons.
Electrons will repel other electrons but are attracted to
protons.
Neutrons are attracted to either protons or electrons.
The interaction between particles is known as an electric
force. Objects that exert an electric force are said to have an
electric charge.
If there are an equal number of oppositely charged particles,
the atom is neither; positive or negative in charge; therefore
it is a neutral particle.
Charged and Neutral Objects
Neutral Object: an object that has an equal number of
protons and electrons.
Negatively Charged Object: is an object that has more
electrons than protons.
Positive Charged Object: is an object that has fewer
electrons than protons.
Objects are made up of particles. An object’s charge
depends on the charge of its atoms. Electrons can move
from one atom to another creating an imbalance. An atom
that gains electrons becomes negatively charged. An atom
that loses electrons becomes positively charged.
Figure 2: a) A Neutral object. b) Negatively charged objects have more electrons than
protons. c) Positively charged objects have fewer electrons than protons. (Note: Each
charge symbol represents a very large number of protons (+) or electron (-).)
Law of electric Charges
Law of Electric Charges: are objects that have opposite
charges attract each other; objects that have like charges
repel each other.
- Objects that have opposite charges attract each
other. Negative attracts positive and positive
attracts negative.
- Objects that have the same charges repel each
other. Negative repels negative and positive repels
positive.
-
Figure 4: a) Count the charges in each object. The rod is negatively charged and the ball
is positively charged. They attract each other. B) Both the rod and the ball are negatively
charged. They repel each other.
The strength of the force between charged objects is related
to distance and amount of charge.
- Electric force decreases as distance increases between
the objects.
- Electric force increases as electric charge increases.
-
Figure 5: a) For a given amount of charge, the amount of force decreases as distance
increases. b) For the given distance, the amount of force increases as the amount of
charge increases.
Check Your Learning:
Questions 1 – 6, pg. 463
Wrap Up:
- Protons have a positive charge. Electrons have a
negative charge. Neutrons have no charge.
- Electrons can move from one atom to another. When
electrons move, they transfer electric charges.
- Protons do not move from one atom to another.
- Neutral objects have an equal number of protons and
electrons.
- When a neutral object gains electrons, it becomes
negatively charged. When a neutral object loses
electrons, it becomes positively charged.
- Charged objects exert an electric force on each other.
Objects with like charges repel each other. Objects
with opposite charges attract each other.
- Electric force increases with an increase in electric
charge and decrease with increasing distance between
the objects.
Try This: Testing Charged Objects
Try This: Moving Objects by Charging
pg. 461