Electricity and Magnetism

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Electricity and Magnetism

• Chapter 19
• Mr. Saks
• General Science
• UNIT FIVE

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Objectives

• Explain the relationship between electrons and
  electricity
• Describe an electrical circuit
• Name two properties of magnets

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Words to Know

• Battery a device that changes chemical energy
  into electrical energy.
• Circuit an unbroken path along which an
  electrical current flows.
• Conductor a material through which electricity
  travels well.
• Discharge the letting go of extra electrons.
• Electrical Insulator a material through which
  electricity does not travel.
• Fuse a weak link in an electrical circuit that
  it designed to break the circuit if it gets too
  hot.
• Generator a machine that turns mechanical or
  heat energy into electrical energy.

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• Magnet a stone, piece of metal, or any solid
  substance that attracts iron or steel.
• Magnetic Field the area around a magnet that
  exerts magnetic force.
• Static Electricity the electricity created when
  objects with opposite charges are attracted to
  each other.

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I. Electric Charge

• Have you ever?
• The crackling of your brush while you do your
  hair?
• Felt a small shock when you touched something
  metal?
• Clothes sticking together when they come out of
  the dryer?

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• We learned about the atom.
• Inside the nucleus are the protons () and the
  neutrons (0).
• Around the outer shell are electrons (-)
• Electrons can be stripped away
• Rubbing a balloon against your head
• Electrons are stripped away from your head to the
  balloon
• Balloon has negative charge
• Your head will be positively charged

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II. Static Electricity

• Negatively charged objects have extra electrons
• Two objects that are negatively charged repel
  each other
• Positively charged objects have lost some
  electrons
• 1. Two objects that are positively charged will
  also repel each other

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• Objects that have opposite charges from each
  other will attract each other
• Why your socks stick to your jeans in the dryer
• Static electricity is created when two objects
  with opposite charges are attracted to each other

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• Most charged objects do not hold their charge for
  long
• Most negative charged objects give up their
  electrons
• Positively charged objects try to collect
  electrons
• Pull your socks from your jeans just after the
  dryer and you could see a spark
• Discharge is the spark of static electricity as
  electrons are exchanged to regain a neutral state

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III. Lightning is a Discharge of Electrons

• Lightning is a huge electrical discharge
• It is like a giant spark between a cloud and the
  Earth
• Lightning can go from cloud to cloud also
• Lightning can also go from ground to cloud
• Clouds build up electrons
• Cloud become attracted to a positive charge on
  the ground
• Electrons jump from the cloud to the tree

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• Lightning
• Nature wants to be neutral in charge
• Lightning is the discharge of electrons from
  cloud to ground to regain a neutral charge
• Thunder
• Lightning is intense light and heat
• The air around the lightning bolt expands very
  rapidly
• This expansion is so fast that it break the sound
  barrier causing the thunder

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Benjamin Franklin

• One of the first scientist to experiment with
  electricity
• 1752 tied a key to a kite and flew it in the
  middle of the thunderstorm
• When lightning hit the kite a spark flew from the
  key
• Proved that lightning had and electrical discharge

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IV. Electrical Currents

• Some materials allow the flow of electricity
  better than others, called conductors
• Metal is an excellent conductor
• Your body can conduct electricity
• Electrical insulators are materials through which
  electricity does not travel

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• Insulators
• Rubber and plastic are good insulators
• Look at your chords from any appliance to the
  wall, it is covered with rubber
• Protects you from the current
• Electricity is the flow of electrons
• Batteries and generators provide this flow, and
  in turn create electricity

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• Batteries
• Batteries change chemical energy into electrical
  energy
• Usually made of two different kinds of metal and
  an acid
• Acid removes electrons from one of the metal and
  adds it to another
• a. One of the metals is positively charged the
  other is negatively charged

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• Two pieces of metal are connected by a conductor
• The positive metal is attracted to the negative
  metal
• Electrons flow through the conductor creating
  electricity
• Generators are often used instead of batteries
• These are machines that turn mechanical energy
  into electrical energy

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Science Practice

• List five ways you use electricity
• Which part of the atom moves in an electrical
  current?
• Why do electrons jump to the Earth in a
  thunderstorm?

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Electrical Circuits

• Many things in your house are powered by
  electricity
• Dishwashers, hair dryers, stereos
• This electricity has to be controlled
• Electricians give electricity paths in which it
  can flow
• The paths are circular
• They come back to the place they started

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• Circuit is an unbroken path along which
  electricity can flow
• This picture is a closed circuit between a
  battery and a light
• Battery produces source of electricity to flow
• Electricity goes around the wire to the light
• Filament in the light heats up and glows
• Electricity continues along the circuit back into
  the battery

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• Some circuits have switches
• If the switch is turned off it is an OPEN circuit
• Electricity cannot flow in an open circuit
• When the switch is turned on, the circuit is
  CLOSED and electricity can flow
• When electricity heats the light some of the
  energy is transformed into What kind of energy?
• Sooner or later, this lost energy will cause the
  battery to die.

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• Series circuit
• This is a path for electricity to flow through
  each electrical appliance without branching off
• If the wire is disconnected in any area, all
  electricity is lost

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• Parallel Circuit
• This is a circuit that has many branches
• This is how your house is wired
• If electricity is cut between 3 and 4 does all
  power go out?
• How about between 6 and 5?
• Allows electricians to narrow down search area
  for electrical problem

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• Fuse
• Fuse is a weak link in a circuit
• Prevents overloaded circuits from causing fires
• Usually made of a metal wire that has a low
  melting point
• When too much electricity flows through the fuse,
  the wire melts and the electrical current stops

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VI. Magnetism

• 2000 years ago the Greeks discovered stones that
  attracted each other
• These stones also attracted iron
• They called them lodestones (natural magnets)
• Magnets are any stone, metal, or solid that
  attracts iron or steel

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• What are some uses for Magnets?
• Magnetic Field
• Each end of the magnet is called a pole
• If you swung a magnet freely one end will always
  point North
• They work the same as electrical charges
• Like poles repel
• Opposite poles attract

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• The area in which the magnetic force is active is
  called the magnetic field
• Magnetic field is strongest at the poles
• When a piece of metal is magnetized all the
  electrons in the metal are lined up
• The tiny fields of magnetism in the electrons
  turn so all North poles face North, or south
  poles face south
• Slamming or heating a magnet will demagnetize a
  magnet