Chapter 11: Electricity and Magnetism

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Chapter 11 Electricity and Magnetism
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Aim What is electricity?
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Electricity

• All matter is made up of atoms
• atoms are made up of protons, electrons and
  neutrons
• Protons and electrons can transmit energy in the
  form of electricity
• When 2 different materials are brought into close
  contract some electrons move to the other
  material
• Causes the material to become electrically
  charged (positive charge or negative charge)

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• Negatively charged-more electrons, less protons
• Positively charged-more protons, less electrons
• Static electricity is produced from the buildup
  of positive and negative charges
• Principles of Electricity
• Opposite charges attract
• Like charges repel

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Aim What is an induced Charge?
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Induced Charge

• When a charged balloon is brought near a wall,
  its extra negative charges repel the negative
  charges on the wall
• The negative charges move to the other side of
  the wall
• The wall becomes positively charged
• The balloon has a negative charge causing it to
  be attracted to the wall and stick

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Aim What are conductors and insulators?
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• Conductors
• Electrons move through a material easily
• Can cause a spark
• Ex human tissue touching metal doorknob
• Insulators
• Electrons do not flow easily through a material
• Ex human tissue touching plaster will not cause
  an electric spark

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Grounding electricity

• It is dangerous to touch a bare wires
• Grounding wires of an appliance connects the
  metal case to the ground through the household
  wiring
• If a dangerous charge builds up the grounding
  wire enables the appliance to share the change
  with the ground
• Grounding wires protect us from getting dangerous
  shocks

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Aim How is lightning produced?
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• Produced by static electricity
• Negative charges build up in a cloud
• The ground has a positive charge
• When enough negative charges build up they form a
  path to the ground
• Surge of electric energy heats the air to glow-we
  see lightning
• Heat makes the air expand rapidly-we hear thunder
• Lightning has high electric energy, which is
  deadly

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Aim What is a circuit?
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Circuit

• A path along which charged particles can travel
• Electrons move through the wires and bulbs
• Consist of a source of electricity, devices and
  connecting wires
• The source of electricity starts pulling and
  pushing on the electrons and the electrons start
  flowing to the positive end of the source
• A flow of charged particles moving through a
  circuit is called a current
• Electrons move from negative to positive

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Resistors

• Sources of electricity are rated by voltage
• As the voltage becomes greater, more negative and
  positive charges can build up at one end
• Resistor-opposes a flow of electrons
• It makes the current smaller by opposing the flow
  of electrons
• The lamp could blow out without the resistor
• The resistor reduces the current of electrons
  flowing through the lamp to a safe level

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Short Circuits

• Short circuit could occur if the current is not
  reduced
• If the current is not reduced, electrons will
  collide causing the wires to heat up
• This heat could cause a fire

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Aim What is the difference between a series
circuit and a parallel circuit?
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Series Circuit

• Only one path for the electric current
• Their voltages are added together
• Increased crowding of electrons at the negative
  end of one battery
• Increased removal of electrons at the positive
  end of the other battery
• Puts more force on electrons in the wires and
  bulbs, which produces more current
• Light bulbs act as a resistor to prevent a short
  circuit from occurring
• The flow of charges is the same at any point

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Parallel Circuit

• More than one path for current
• Electricity source makes each path feel the same
  overcrowding of electrons
• Total current increases when another path is
  added, even though another resistor is present
• Current in each path depends on the strength of
  its resistor
• Currents are added together to find the total
  current
• Total current is the same at any point

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Aim What is the difference and open circuit and
closed circuit?
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Open Circuit

• Incomplete circuit
• Switch is in the off position
• There is no current
• Electrical devices do not receive electric energy
• Copy circuit 1 in Notebook

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Closed circuit

• Complete path for a current
• Current flows in the wires and devices
• Current transfers energy to the device
• Switch is in the on position or closed
• Copy Circuit 2 in Notebook

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Aim What is a magnet?
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Magnets

• Attract metal objects made of iron, cobalt or
  nickel
• Attract and repel other magnets
• Have 2 poles north-seeking pole and a
  south-seeking pole
• South pole of one magnet repels the south pole of
  another
• A north magnetic pole attracts a south magnetic
  pole
• The attraction is strongest at the poles

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• Magnetism comes from the motions of electrons in
  atoms
• Moving electrons cause atoms to line up in the
  same direction
• Permanent magnets-atoms always stay lined up
• If brought near and object that is nonmetallic,
  there is no attraction

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Electromagnets

• Devices that are made magnetic by an electric
  current
• Magnetism results from moving electrons in a
  current-carrying wire
• If brought near a nonmetallic object, there is no
  attraction

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Aim how is a magnetic Field Produced?
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Magnetic Field

• Is the area around a magnet in which other
  magnets can feel attraction or repulsion
• Magnetic force moves from the north pole to the
  south pole and form closed loops
• Attraction or repulsion is strongest where the
  arrows are most crowded

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Earths Magnetic Field

• Tilt of Earths axis causes the magnetic poles to
  be off true geographic north and south poles
• Magnetic field is not evenly shaped
• Compass needle always points to the magnetic
  north pole
• Earths magnetism is likely caused by electrical
  currents in a fluid metal layer around Earths
  inner core

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Aim What are the uses of Electromagnets?
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Electric Motors

• Used to power toys, elevators, fans, air
  compressors, cranes, some cars and bicycles
• The spinning force comes from an electromagnet
• A loop of wire is placed between 2 permanent
  magnets
• When current passes through the wire, the loop
  becomes an electromagnet

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Medicine

• Magnetic resonance imaging (MRI)
• Strong magnetic field produced by electromagnets
  cause the nuclei in the patients body to behave
  like magnets and line up with the magnetic field
• This enables radio waves to produce images of
  tissues inside the body

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Sound

• Speakers depend on electromagnets to operate
• Cone in a speaker has an electromagnet
• Current passes through the electromagnet causing
  the cone to vibrate and produce sound

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Aim What is the difference between a wet cell
and a dry cell?
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Wet Cell

• A device that produces a current in a solution
• Use chemical reactions to produce an electric
  current
• Charged particles always move in the same
  direction-direct current
• Consists of 2 different metal plates in a
  solution
• Produces a voltage-the difference in the amount
  of potential energy between the plate
• Voltage is measured in volts

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• The amount if current can be measured by an
  ammeter and the unit is ampere or amp

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Dry Cell

• Produce an electric current using a moist
  conducting paste
• Chemical reactions between the paste and the
  plates produce a current
• Ex battery

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Aim How does electric current reach your home?
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Generators

• Uses mechanical energy to make electricity
• It produces an alternating current
• Electric power plants use generators to produce
  electricity for homes and businesses
• Transformers are used to increase or decrease the
  voltage of the current

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Power Plants

• Electric current produced by huge generators
• Power lines connect the power plants to homes in
  cities and towns
• Electric current from a generator first passes
  through a transformer that increases the voltage
  anywhere from 120,000 to 500,00 volts
• Before the current comes into our homes it passes
  through another transformer that decreases the
  voltage

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• Household circuits use 120 volts
• The total current for an entire house is 100 or
  200 amps
• You can run two appliances on the same circuit,
  which has 20 amps, as long as they do not use
  more amps combined
• Short circuits occur when too much current flows
  through a wire
• Fuses and circuit breakers protect homes from
  catching on fire

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Aim How do you use electrical energy at home?
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• Any form of energy can be changed into other
  forms
• Electrical energy can be changed into 4 other
  types of energy
• Mechanical Energy
• Electric energy changes into mechanical when any
  device that uses a motor is used
• Examples food blenders, electric fans, power
  tools

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• Heat
• Coils get very hot because of an electric current
• Electrons from the current collide with the atoms
  in the coils
• Temperature of the coils rise
• Ex heaters, electric blankets, toasters, hair
  dryer
• Sound
• Current causes electromagnets to move a diaphragm
  back forth producing sound waves
• Ex speakers

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• Light
• 2 types of light bulbs
• Incandescent
• Contain a thin metal wire or filament that acts
  like a resistor
• Electric current heats it causing the filament to
  give off heat and visible light
• Only 12 of the energy is light
• Rest of energy is wasted as heat

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• Fluorescent
• Produce more light than heat
• Series of collisions causes gas inside the glass
  to produce light
• Fluorescent coating on the outside glows