Chapter 12 – Static and Current Electricity
12. 1 Protons and electrons attract (pull together) each other. This
force of attraction or repulsion is known as electric force. Objects that
exert an electric force are said to have an electric charge.
When there are equal number of protons and electrons in an atom, the
charges are balanced or neutral.
Particle
Proton
Neutron
Electron
Neutral Object
Electric Charge
Positive
No charge
Negative
Location
Nucleus
Nucleus
Outside nucleus
Negatively charged object
Particle Symbol
p+
n0
e-
Positively charged object
Law of Electric Charges which states the following:
 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.
12. 2 Static Electricity and Discharge
Static Electricity: an imbalance of electric charge at rest on the surface of an
object.
Electric Discharge: the rapid transfer of electrons from one object to another.
Example: lightning and photocopier.
12.3 Charging by Contact
Charging by friction: the charging of two neutral objects made of different
materials by rubbing them together.
The hair and the comb start out electrically neutral. After combing, the comb is
negatively charged and the hair is positively charged.
* Charged objects tend to lose their charge quickly in humid weather. In dry
weather objects are less likely to lose charge and they will remain charged,
making your hair more prone to static electricity *
Charging by Conduction – charging an object by contact with a charged object
The negatively charged rod transfers
electrons to the sphere by direct
contact. The sphere gains a negative
charge by conduction.
12. 4 Think back to the pith ball
electroscope as seen in the you tube
videos. What happened when the
ebonite rod was charged?
12.5 Charging by Induction: charging a neutral object by bringing another
charged object close to, but not touching, the neutral object.
Induced charge separation: a shift in the position of electrons in a neutral object
that occurs when a charged object is brought near it.
When a negatively charged balloon is brought near a neutral wall, the part of the
wall near the balloon is temporarily charged by induction. The positive charges on
the surface of the wall attract the balloon.
Charging More Than One Object By Induction
Two identical neutral spheres are in contact. A charged balloon induces the movement
of electrons. Separating the spheres prevents further electron transfer. Both spheres
have been charged by induction.
Grounding: connecting an object to a large body, like Earth, that can remove an
electric charge from the object.
The person’s hand is negatively charged. The faucet is neutral. The excess electrons
move from the hand through the faucet to the ground. Both the hand and the faucet are
neutral.
A negatively charged rod induces a positive charge on one side of the pith ball. Electrons
that moved to the other side of the ball can travel to the ground. Removing the ground
before the charged rod is moved away leaves the ball permanently charged.
Refer to Static Electricity Lab
12.8 Moving Charges
Conductor – a material that transmits thermal energy or
electrical energy easily. Copper wire is used in many electrical
applications because it is a good conductor of electricity, does
not easily corrode, and is inexpensive.
Insulator – a material that resists or blocks the flow of
electrons through it. Example: glass and ceramic.
Conductivity – a measure of a material’s ability to conduct
electricity.
Current Electricity
Electric current – the flow of electricity through a conductor in a closed path. Batteries
are the most common source of electric current to power small electrical devices.
Direct current (DC) – an electric current in which the flow of electrons travels in one
direction only. The flow of electrons in one direction from the battery through a
conductor (wires) to a device and then back to the other end of the battery.
The Grid
Alternating (AC) – an electric current that repeatedly reverses direction.
Travels over transmission lines from a generating plant to your home by the
electrical energy distribution grid.