Download Science Part B Chapter –4- Electrical Energy Lesson –1

Science
Part B Chapter –4Electrical Energy
Lesson –1Most atoms have equal numbers of protons, which are positively
charged, and electrons, which are negatively charged. These atoms
have no charge; they are neutral.
When objects come in contact or are rubbed together, their atoms
can gain or lose electrons. An atom with more electrons than
protons is negatively charged. An atom with more protons than
electrons is positively charged.
Opposite charges attract each other, and like charges repel each
other.
The force of attraction or repulsion between two charges is related
to the magnitude of each charge.
The force decreases as the distance between the charges
increases.
Sparks may be created when electrons jump from a negatively
charged area toward a positively charged area.
Lightning results from the movement of large numbers of electrons.
Lightning is a giant spark of electric charges moving between a
cloud and the ground, between a cloud and another cloud, or within
a cloud.
The steady flow of electric charges in a wire path is an electric
current.
It differs from electric charges such as lightning because it can be
switched on and off and used to power appliances.
Its path is called an electric circuit.
A material through which electricity can easily flow is a
conductor.
A material through which electricity cannot flow is an insulator.
Lesson –2The electricity that most people use in their homes originates at a
power plant and passes through high-voltage wires. Near the home,
the electricity passes through a transformer, which reduces the
electrical voltage to the levels used in a home.
A home has many circuits. Electricity flows through these circuits
to various electrical devices.
Each circuit in the home begins and ends at the circuit box.
A switch is the part of a circuit that closes the circuit and allows
electricity to flow or opens the circuit and prevents the flow of
electricity.
Special switches are used in homes to protect people from fire and
other electrical hazards.
Circuit breakers and fuses prevent too much current from flowing
through a circuit.
GFCI outlets (ground fault circuit interrupters) are special outlets
with a safety switch that instantly switches off in some dangerous
situations to help prevent a shock.
The volt is a unit used to measure how strongly the electrons in a
wire are pushed.
Most appliances in the home use 110V electric current. Electric
stoves and a few other devices use 220V current.
Watts or kilowatts measure the rate at which electrical energy is
used. A kilowatt equals 1000 watts.
The total amount of electrical energy that a person uses in
operating an appliance depends on how fast the appliance uses
energy and on how long the appliance is used.
Electric companies measure the amount of electrical energy you use
in kilowatt-hours.
Lesson –3Electricity can make magnetism, and magnetism can make
electricity.
An electromagnet is a device that uses electricity to produce
magnetism.
If a magnet is moved near a wire that is part of a closed circuit,
the changing magnetic field causes current to flow in the wire.
A generator is a device that uses a magnet to change mechanical
energy into electrical energy.
The three basic parts of a generator are the drive shaft, a strong
magnet, and a coil of wire.
Various sources of energy may be used to turn the drive shaft of a
generator.
When a fossil fuel, such as coal or oil, or a nuclear reaction is
used, it produces steam, which turns the turbine connected to the
drive shaft.
Water, wind, tidal and wave energy may also be used to turn the
turbine.
Batteries and solar panels produce electrical energy without using a
generator.
The electrical energy produced by generators is transmitted by
power lines to homes and businesses.