Unit E: The Characteristics of Electricity
11.1 What is Static Electricity
pg. 465
Key Concepts:
1. Static electricity results from an imbalance of electric charge on the surface of an
object.
2. There are many useful applications of static electricity.
Atomic Structure and Electric Charge
Electric Charge: a form of change, either positive or negative, that exerts an electric
force.
- All matter is made up of Atoms.
- The sub – atomic particles that make up atoms are; protons (p+), neutrons (n0), and
electrons (e-).
- Protons and neutrons are contained in the Nucleus of the atom.
- Electrons are found in the space surrounding the nucleus, Electron Energy Shells or
Orbits.
- When protons and electrons are equal for an atom then the atom has a neutral charge.
- If an atom has more protons then electrons, the atom will have a positive charge.
- A positive ion has lost one or more electrons.
- If an atom has more electrons then protons, the atom will have a negative charge.
- A negative ion has gained one or more electrons.
Figure 2: A lithium atom. Electrons (blue) move in the space surrounding the nucleus of
an atom and can be transferred from atom to atom. Electrons and protons carry the
electric charges within an atom.
Table 1: Properties of the Particles of an Atom
Particle
Electric Charge
Location
Positive
Nucleus
Proton
No charge
Nucleus
Neutron
Negative
Outside nucleus
Electron
Particle Symbol
p+
no
e-
Positive, Negative, and Neutral Objects
Neutral object: an object that has equal numbers of protons and electrons.
Negatively charged object: is an object that has more electrons than protons.
Positively charged object: is an object that has fewer electrons than protons.
Static Electricity: an imbalance of electric charge on the surface of an object.
- The atoms in large objects contain a large number of atoms, positively and negatively
charged.
- It is not possible to draw each charge atom in diagrams. Therefore charge symbols are
used to represent charged objects.
- The symbol for a large number of protons is (+) and the symbol for a large number of
electrons is (-).
- The symbols are used to represent the abundance and distribution of charges in an
object.
Figure 3: a) Bohr-Rutherford diagram can be used to show the electrons and protons in
an individual lithium atom, b) objects contain billions of individual atoms. c) the “+” and
“-“, symbols on the object represent the relative numbers of protons and electrons and
their distribution.
- For a neutral object, there will be an equal number of positive and negative charged
symbols.
- For a positive object, there will be more positive charges then negative charges.
- For a negative object, there will be more negative charges then positive charges.
- Objects can become charged when they gain or lose electrons as they are transferred
between objects.
- A neutral or positive charged object becomes negatively charged as they gain electrons.
- A neutral or negative charged object becomes positively charged as the lose electrons.
- Most objects are electrically neutral charge
- When two different neutral objects are rubbed together, they can transfer electrons.
- Both objects become charged, one loses electrons, while the other gains electrons.
- An imbalance of charge between the two objects is called Static Electricity.
Figure 4: a) Neutral objects have equal numbers of protons and electrons. b) Negatively
charged objects have more electrons than protons. c) Positively charged objects have
fewer electrons than protons.
Detecting Static Electric Charges
- An electroscope is used to detect the presence of electric charges.
- A pith ball electroscope can be used to determine a presence.
- How the neutral pith ball reacts will determine if there is a charge, an attraction means
there is a charge.
- If the pith ball is charged, positive, and moves away from an object the object has a
positive charge. (Like charges repel)
- If the pith ball is charged, positive, and moves towards the object, the object has a
negative charge. (Opposite charges attract)
Figure 5: A pith ball electroscope is a simple device that can be used to detect the
presence of electric charges.
The Law of Electric Charges
Electric Force: the force exerted by an object with an electric charge; can be a force of
attraction or a force of repulsion.
* Objects that have like charges repel each other.
* Objects that have opposite charges attract each other.
- The strength of the charge is determined by the amount of charge each object has and
the distance between the objects. An increase in charge increases the attraction. The
greater the distance the less of an attraction between objects.
Figure 7: a) both objects are negatively charged and repel each other. This causes the
pith ball to move away from the metal rod. b) When the pith ball and metal rod are
oppositely charged, they are attracted to each other and the pith ball moves toward the
rod.
Attraction of Neutral Objects to Charged Objects
Induced Charge Separation: is a shift in the position of electrons in a neutral object that
occurs when a charged object is brought near it.
- Neutral objects have an equal number of positive and negative electric charges.
- When a charged object approaches a neutral object, it causes the electrons to either
move towards or further away form the approaching charged object. This is called
induction. The neutral object becomes attracted to the charged object.
- Induction is supported by the Law of Electric Charges.
- Positive charged objects causes the electrons to move closer to the surface towards the
positive charged object, attraction occurs.
- Negative charged object causes the electrons to move further from the surface, away
from the negative charged object, attraction occurs.
- Once the charged object is removed, the original neutral object returns back to normal, a
neutral charge.
Figure 8: the side of the pith ball facing the negatively charged metal rod now has a local
positive charge and is attracted to the metal rod. The force of attraction is greater than the
force or repulsion because of the differences in distances between the charges.
Using a Metal Leaf Electroscope to Detect Electric Charge
- A metal Leaf Electroscope is more sensitive then the pith ball electroscope.
- When the metal ball is touched with a charged object, the metal leafs will take on the
same charge as the object. The leaves will then repel each other.
Figure 10: A metal leaf electroscope a) is used to detect electric charge. When a
negatively charged object is brought near the electroscope electrons are transferred into
the leaves, which causes them to repel and spread apart b) until the charged object is
removed c).
Using Static Charges
- The use of the properties of static charges is a branch of science called Electrostatics.
Electrostatic Paint Sprayers
- When paint leaves the sprayer, the paint is charged. The object is also charged, the
opposite to the paint particles. This causes an attraction between the paint and the object.
- Minimizes paint waste or over spray.
Figure 11: the charged paint particles are attracted to the oppositely charged object.
Evidence of Learning …. Students can
- Explain that an electrically neutral object has equal numbers of positive (protons) and
negative charges (electrons).
- describe static electricity as an imbalance of electric charges.
- explain how path ball electroscope can detect the presence of electric charges.
- use the Law of Electric Charges to predict how charged objects will interact.
- explain how a neutral object can be attracted to a charged object.
- explain how electrostatic painting systems operate.
Check Your Learning
Questions 1 – 9, page 471
Summary:
- Static electricity is an imbalance of electric charge on the surface of an object.
- Electric charge is a property of the particles of atoms. Protons have appositive charge,
electrons have a negative charge, and neutrons have no charge.
- Electrons can be added to, or removed from, atoms.
- When two different materials come in contact, electrons can be transferred between
them, causing an imbalance in charge.
- Neutral objects have equal numbers of protons and electrons. Negatively charged
objects have more electrons than protons, and positively charged objects have fewer
electrons than protons.
- Objects can become positively charged by losing electrons so that there are fewer
electrons than protons.
- Objects can become negatively charged by gaining electrons so that there are more
electrons than protons.
- The Law of Electric Charges states that like charges repel while unlike charges attract.
- A charged object can be used to induce a charge separation in a neutral object.
- A metal leaf electroscope can be used to detect the presence of an electric charge.
- Static electricity has practical application.