Unit E: Electrical Applications
Chapter 12: Static and Current Electricity
12.8: Moving Charges
pg. 484
Key Concepts:
1. Electricity describes how electrons move from one place
to another.
2. Current electricity is generated by moving electrons is a
closed path.
Conductors
Conductor: a material that transmits thermal energy or
electrical energy easily.
A conductor is a material that allows electrons to travel
freely through it, like copper wire in the electrical wiring in
your house. Metals (aluminum, silver, and gold) are
excellent conductors of electricity.
Pure water is a poor conductor of electricity, but water with
minerals dissolved in it is an excellent conductor.
Insulators
Insulator: is a material that resists or blocks the flow of
electrons through it.
Insulators (plastic, glass, rubber, air, and wood) are
materials that have more tightly bound electrons and resist
losing them.
Insulators are used to prevent conductors from transferring
charges, and are used to protect us from dangerous effects
of electricity flowing through conductors. Wires with
plastic coating are insulated.
Conductivity
Conductivity: a measure of a material’s ability to conduct
electricity.
Selecting what is an insulator or conductor is based on a
range of conductivity. The relative ability to conduct
electricity and allow electrons to flow through it is
conductivity, different materials fall along a range of
conductivity.
Least conductive material is an insulator and the greatest
conductive material is a conductor.
Figure 4: Insulators and conductors actually fall along a range based on increasing levels
of conductivity
Current Electricity
Electric Current: is the flow of electricity through a
conductor in a closed circuit.
Direct Current (DC): is an electric current in which the
flow of electrons travels in one direction only.
Electronic devices run on electricity, but can not use static
electricity. Electricity must flow from an energy source
through conducting wires and back again. This must be a
closed circuit or path way, the electricity goes from the
source and back again.
Batteries
Figure 5: A dry cell battery converts
the chemical energy generated by
reactions between chemicals inside it
into electrical energy.
In a battery, chemical reactions release electrons as they
move internally from positive to negative terminals. The
electrons need to move from the negative terminal to the
positive terminal, but the only way to do this is to flow a
path back, but can not return the way it came.
The flow of electrons in one direction is known as direct
current (DC). The wires and devices resist electron flow
through them.
The Grid
Alternating Current (AC): is an electric current that
repeatedly reverses direction.
Electric current travels to your house through the electrical
energy distribution grid, (power grid). Energy is produced
by the generator, when an energy source (fossil fuel,
nuclear, or hydro) turns a turbine, causing the generator to
turn. The spinning coils of the generator between magnets,
produces an alternating current (AC). The electricity flows
in wires in one direction and then reverses and goes in the
other direction. Alternating current is used to supply
electricity to our homes and electronic devices.
Alternating current must travels to a transformer so it can
be transmitted over long distances.
Figure 6: the grid consists of a generating plant with its electric generator, the substation,
transmission lines, transformers at the substation, and the poles leading electrical wires
into your home.
Check Your Learning:
Questions 1 – 6, pg. 488
Wrap Up:
- Electrical conductors are materials that allow electrons
to flow through them easily.
- Insulators are materials that resist or block the flow of
electrons.
- Conductivity is a measure of a material’s ability to
conduct electricity.
- Electric current is the flow of electrons through a
conductor.
- Direct current is current that flows through a
conductor in one direction only.
- Alternating current is current that repeatedly reverses
direction.
- Electric current travels over transmission lines from a
generating plant to our home by the electrical energy
distribution grid.