Electricity and Magnetism

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Electricity and Magnetism
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Atomic Review

• An atom consists of 3 particles
• Protons-positively charged
• Neutrons-no charge
• Electrons-negatively charged

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What is Electricity?

• A form of energy caused by moving electrons.

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How charges act

• Like charges repel
• Opposites charges attract
• Electrons flow from a negatively charged area to
  a positively charged area

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• Most objects are electrically neutral

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Static Electricity
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Phenomena

• Lightning
• Leather car seats
• Ben Franklin and the kite.
• Sliding your feet on a rug

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How are charges transferred?
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• When you rub two substances together you do work
  and thus you add energy.
• This removes electrons from one substance and
  adds it to the other.

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This creates IONS which are charged particles.
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Summary

• The energy used to rub two things together is the
  energy that gets involved in removing and
  transferring electrons.

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Electrical Charge

• Can be Transferred.
• It cannot be created or destroyed.

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Conductors

• A conductor allows charges to flow easily
• Some conductors are better than others
• Examples
• Copper
• Iron

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Insulators

• An insulator prevents electric charges from
  flowing easily
• Examples
• Rubber Cork
• Wood Plastic

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Electric Current

• Electric Current is the flow of electrons
  through a conductor
• There are two types of electric current
• Alternating Current
• Direct Current

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Alternating Current

• Changes direction at a regular rate
• Most commonly used type of electricity because it
  does not create as much heat
• Examples
• Appliances
• Houses
• Christmas lights

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Direct Current

• Always flows in one direction
• Always flows from negative to positive
• Example
• Battery
• Creates a lot of heat

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What is a Battery?

• A series of electrochemical cells
• Two types
• A wet cell
• A dry cell

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Wet cell

• Electrolyte is a liquid
• Example
• Car battery

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Dry cell

• Electrolyte is a moist paste
• Example
• AA battery

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What is a circuit?

• The path an electric current follows
• Consists of four parts
• Source Load
• Wires Switch
• Current flows only through a closed circuit

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Diagrams

• Source Resistance
• Lamp Motor
• Wire
• Switch

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What is a series circuit?

• A circuit where current follows only one path
• If one light goes out, the whole circuit goes out

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Diagram of a Series Circuit
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What is a parallel circuit?

• Current follows more than one path
• If one light goes out, the others remain on.
• Used in
• Homes
• Schools
• Buildings

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Diagram of a Parallel Circuit
Circuit diagrams are a pictorial way of showing
circuits. Electricians and engineers draw circuit
diagrams to help them design the actual circuits.
Here is an example of a circuit.                  
                                                  
       
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What are volts?

• Electromotive force (EMF) is the force that moves
  electrons in a circuit.
• A volt is the unit used to measure EMF.

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What are amps?

• The amount of current depends on the number of
  electrons flowing in the circuit.
• An ampere (amp) is the unit used to measure
  current.

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What are ohms?

• Resistance opposes the flow of electrons in a
  circuit.
• Resistance of a wire depends on length,
  thickness, material, and temperature.
• An ohm is the unit used to measure resistance.

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Magnetism
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Where do magnets come from?

• Earth is a magnet
• Iron can be made into magnets
• 3 things stick to magnets iron, nickel, cobalt

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Magnetic Pole

• A pole is the area of the magnet where the
  magnetic effect is the strongest.
• One pole of the magnet will always point north
  this is the north pole.
• The south pole will point south.
• The north and south poles are unlike and
  therefore attract.

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Magnetism

• Magnetic
• Fields

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Magnetic Fields

• Exist in regions surrounding magnets.
• Exerts a torque on a compass needle. (Demo)
• Compass needles allow us to map out magnetic
  fields.

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• Magnetic field lines flow out of the north pole
  and into the south pole.
• They are continuous and never cross

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The Earth itself is a magnet!
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• Earths magnetic field causes compasses to line
  up.
• Magnetic north/south pole is about 11º off from
  geographic north/south pole.

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Why?

• Scientists are not sure why the Earth is a giant
  magnet but some believe that it is due to the
  circulation of molten metal (iron and nickel)
  within the Earths core.

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Oersteds Discovery!

• The presence of an electric current in a wire
  causes a torque in a compass nearby.
• A current carrying wire generates a magnetic
  field.
• Electromagnetism.

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Electric Current

• The flow of charge through a material
• The amount of charge that passes through the wire
  in a unit of time is the rate at which the
  electric current flows. The unit of current is
  the ampere or amp.

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An electric current produces a magnetic field.
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The direction of the current determines the
direction of the magnetic field in a current
carrying wire.
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Cause

• All magnetism is caused by the movement of
  charges.

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Electromagnet

• An electromagnet is a strong magnet that can be
  turned on and off.

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Increase strength

• Increase the strength of a magnet by
• Increasing the current
• Increasing the number of loops of wire to the
  solenoid.
• Wind the coils of a solenoid closer together.
• Use stronger ferromagnetic material for the core.