Current Electricity - The Big Ideas
• Electricity flows through a circuit to light light bulbs and
cause other things to work.
• An electric current is a steady flow of charged particles.
• Electrically charged particles moving in a current must have
a closed circuit path.
• Circuits usually include wires made of metal and other
materials that conduct electricity.
• Metals such as copper and iron readily conduct electricity
and are used in wires to help the flow of electricity.
• Insulators, such as rubber and wood, conduct electricity very
poorly.
• Electrical energy can be changed to other forms of energy,
such as a toaster turning electrical energy into heat.
Current Electricity - Common Misconceptions
• Current flows around a complete circuit, but it is used up by
objects like light bulbs so less current retunls than leaves the
source of the electricity.
- Reality: An electric current is a steady flow of charged
particles. Electrical energy can be changed to other
forms of energy, but it is not created or destroyed. It is
conserved.
• Wires are hollow like a water hose, and electrons move
inside the hollow space.
- Reality: During a direct current in a simple circuit, the
flow of charges takes place throughout the entire wire,
which is not hollow.
Some people carry jumper or booster cables in the
trunks of their cars. They use them in case their car
batteries die. They may also use them to help other
drivers when their batteries die. You may have seen
someone use jumper cables to get a car started.
You may have noticed two things about the jumper
cables. First, there are two cables. Second, each cable
is made of metal and plastic.
Just one jumper cable would be useless. Jumper
cables must be a pair because you need two cables to
make a circuit. A circuit is a closed pathway or loop.
An electric circuit is a closed pathway through which
electricity flows. One jumper cable allows electricity
to flow from the good battery to the dead battery.
The other jumper cable allows the electricity to flow
from the dead battery back to the good battery.
The second jumper cable completes the circuit.
When a car battery dies, people can use jumper
cables to start the car.
A circuifusually includes wires made of metal. Jumper cables
contain wires made of copper. Like all-metals, copper is a
conductor. A conductoris a material that allows electricity to flow
through it.'The flow of electricity is called an electric current.
Electric 'current flows through jumper cables very easily.
Jumper cables withouta plastic covering would be dangerous.
If you touched them, electricity could flow through your body.
It could hurt or even kill you. The plastic keeps electricity from
flowing into other objects from the wire. It can do this because
plastic is an insulator. An insulator is a material that does not
allow electricity to flow through it easily. The plastic covering on
jumper cables keeps people from getting shocked. Rubber, wood,
and glass are also insulators.
When a car battery dies, it can be a real pain. But the next time you
see someone using jumper cables, you will know how they help let
electricity flow.
Discovery Education Science
© 2007 Discovery Communications, LLC
In the 1800s, horses pulled people
on trolleys through city streets. In
1887, the city of Richmond,
Virginia, decided to look for a better
way to move their trolleys. They
hired a scientist named Frank
Sprague. Sprague had worked as an
assistant to Thomas Edison, the
inventor of the light bulb. Edison
was interested in using electricity to
produce light. Sprague was
interested in using electricity to
produce power. Sprague thought
electricity might be able to replace
the horses that were used to move trolleys.
Horse-drawn trolley in New York City
In 1888, Frank Sprague invented a way to use electricity to run a trolley. He
used an electric current. An electric current is a steady flow of charged
particles. The charged particles in an electric current must flow through a
special loop called a circuit. You can think of an electric circuit as being
like a race track. The cars keep moving around the track. In an electric
circuit, the charged particles keep moving around in a loop.
Sprague had to build an electric circuit through the streets of a city to make
his trolleys run. He did it by building power ~.,.....~_ ...;;
lines in the air. A machine called a generator
makes the electric current. The electric
current flows through the power lines and
down a metal pole on the trolley. The current
then flows to motors on the trolley. The
electric current turns the motors, and the
motors move the trolley. The current flows
back to the generator through metal tracks in
the street. Then the electric current can begin
another trip through the circuit. As long as
electric current flows through the circuit, a
Electric trolleys in Atlanta, Georgia
trolley can keep running.
Discovery Education Science
Communications, LLC
© 2007 Discovery
Because of Sprague's invention, Richmond became the first city with
electric-powered trolleys. After he invented the electric trolley, Sprague
decided to use an electric current to move people in a different direction­
straight up. He invented the electric elevator!
Discovery Education Science
Communications, LLC
© 2007 Discovery
You must throw a switch to turn on a light. You must push a
button to ring a doorbell. You must press down on the
toaster to heat the bread. What happens when you throw the
switch, push a button, or press down on the toaster?
You allow electricity to flow.
Electricity must flow through a circuit to do work.
A circuit is a special closed pathway for electricity.
To understand what a circuit is, imagine the
following:
• Cut a piece of string.
• Place the string on a table and stretch it out.
• Move your finger along the string. You start
at one place and end at another place. The
string represents an open pathway.
• Now tie the two ends of the string together.
• Again use your finger to trace the string. No
matter where you start, you wind up at the
same place. This time, the string represents
a closed pathway.
When you turn on a light switch, you allow
electricity to flow.
An electric circuit is a closed pathway that includes
three parts. One part is an energy source, such as a battery.
The energy source provides charged particles.
Wires are the second part of a circuit. Most wires are made of
metal, such as copper or iron. Charged particles flow easily
through metals such as these. Metals are called
conductors. A conductor is anything that allows charged
particles to flow through it.
The third part of a circuit is called the load. The load can be a
lightbulb, a doorbell, a toaster, or another electric device.
Wires connect the load to the energy source to complete the
circuit. Once the circuit is complete, electricity can start
flowing. The flow of electricity is called an electric current.
The electrical energy that flows through a circuit can change
into other forms of energy. For example, a toaster changes
electrical energy into heat energy. All you have to do is
complete the electric circuit by pressing down on the toaster.
Get out the butter and jelly!
Discovery Education Science
© 2007 Discovery Communications, LLC