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Electricity & Magnetism. Universal Forces Throughout all galaxies far, far away………. Remember, FORCES exert a push or pull on objects and can do WORK They can act over a distance without touching Gravitational force – a weak force due to mass

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universal forces throughout all galaxies far far away
Universal ForcesThroughout all galaxies far, far away………
  • Remember, FORCES exert a push or pull on objects and can do WORK
  • They can act over a distance without touching
    • Gravitational force – a weak force due to mass
    • Electromagnetic force – a stronger force due to charged particles
        • ELECTRICITY
        • MAGNETISM
what is a charge
What is a charge?
  • All matter is made up of atoms
  • All atoms are made up of :
    • Protons (+)
    • Neutron ( 0)
    • Electrons (-)
  • Electrons extremely SMALL mass
    • travels extremely FAST
    • has A LOT of KINETIC energy !
what is a charge1
What is a charge?
  • Atoms are normally NEUTRAL because:

# of PROTONS = # of ELECTRONS

  • Electrons can move easily between objects
  • When an object LOSES electrons  positively charged

# of PROTONS > # of ELECTRONS

  • When an object GAINS electrons  negatively charged

# of PROTONS < # of ELECTRONS

  • This movement of electrons can transfer energy and do WORK.
check for understanding what would occur to make a positive or negative particle
Check for UnderstandingWhat would occur to make a positive or negative particle?

+

-

-

+

+

+

-

-

+

+

-

-

-

NEGATIVE

POSITIVE

law of charges
Law of Charges
  • Like charges REPEL or PUSH (+ and +) OR ( - and -)
  • Unlike charges ATTRACT or PULL (+ and - )
  • FORCE is exerted by electric charges!
check for understanding would the following repel or attract each other
Check for Understanding:Would the following repel or attract each other?
  • REPEL
  • ATTRACT
  • REPEL

-

-

and

-

+

and

+

+

and

slide8
Electrons (-) push each other away
  • Electrons (-) are pulled toward protons (+) or other positively charged objects
induction
Induction
  • Some objects that really have an equal amount of charges, can temporarily shift their electrons so that an area may become more positive or negatively charged.
static electricity
Static Electricity
  • Charges that build up is called static electricity.
    • Pollution control systems to capture smoke particles
    • Photocopiers, speakers, microphones
    • Lightning
    • Muscle cells
    • However, in general, static electricity is a nuisance!
    • Van der Graaf and Rockin’ Bill Nye
static discharge
Static discharge
  • Discharge is a sudden movement of electrons
    • Unpredictable
    • Unreliable
    • Its just not really useful.
  • Static discharge occurs when a new path forms between two areas of opposite charge.
  • The electrons move suddenly to try to restore the balance between charged areas.
electric current
Electric Current
  • Static discharge is brief and limited in the number of electrons it moves.
  • To do USEFUL WORK, we need a continuous flow of charge.
  • This is an electric current.
electric current cont
Electric Current, Cont.
  • For an Electric Current, we need…
  • A steady supply of moving electrons
  • A path for the electrons to follow and return to be reused.
  • Something to “push” the electrons along the path.
water analogy
Water Analogy
  • Water in a high reservoir (PE) causes a downward force through pipes to a lower reservoir.
  • The higher the reservoir, the higher the PE.
  • Water flows through pipes in a continuous path. Higher reservoir creates flow with more KE.
  • Water is pumped back up to the higher reservoir to be re-used.
the electric circuit
The electric circuit…
  • Electrons “flow” along a closed path with no breaks.
  • Battery chemicals provide the “push” of electrons, acting as a “pump”. (ELECTRICAL FORCE )
  • The “strength” of the battery provides the PE of the circuit.

Work is done as electrons flow through a circuit .

circuit construction
Circuit Construction
  • pHet Circuit Construction interactive
let s talk numbers
Let’s talk numbers!
  • A battery is a device that converts chemical energy to electrical energy.
  • In a battery , one terminal (end) is Positive and the other terminal (end) is Negative.
  • The PE of the electrical flow of electrons from one end to the other is the voltage of the battery.
  • Higher voltage = Higher “push” of electrons through the circuit (Joules/Coulomb)
let s talk numbers1
Let’s talk numbers!
  • Coulomb (C)
    • Is a bunch of electrons (6.25X 1018 electrons)

6,250,000,000,000,000,000 electrons

  • 1 Volt is the PE that can move 1 Coulomb of charge using 1 Joule of energy
  • Ampere(amps) is 1 Coulomb in one second ( C / s)
what if we add a water wheel
What if we add…a water wheel ?
  • A wheel would hinder the flow – like friction.
  • Water uses some of it’s energy to make the wheel turn (work)
  • Water flows on through the wheel to continue the flow.
  • More than one wheel could be put into the flow of water.
resistors
Resistors
  • Resistor = any object or substance that slows down the flow of electrons.
  • Electrons transfersome of their Kinetic energy when going through a resistor, so this is a place of energy conversion:
      • Light bulb  light energy
      • Heating element  thermal energy
      • Speaker  sound energy
  • Resistance measured in ohms. (Ω)
a short circuit
A short circuit:
  • Resistors also protect a circuit from becoming a SHORT CIRCUIT!
  • Too much current!!
  • Wires get HOT!
  • Plastic covering can melt.
  • Fire may start.
  • Drains battery fast – or flips protective circuit breakerin electrical panel.
magnetism
Magnetism
  • Early discovery of natural occurring lodestones
    • they always oriented themselves north when floated on a piece of wood on water and
    • they concentrated iron shavings
  • There are Naturally occurring magnets and Man-made magnets.
  • Current science understands magnets to ALWAYS have a NORTH and a SOUTH pole, no matter how many times you divide a magnet(Di-Pole)
effects of magnetism
Effects of Magnetism
  • Magnetic fields show the strength and direction of magnetic forces.
    • Closer lines = more strength
    • Force lines point from north pole to south pole
  • Same poles REPEL
  • Opposite poles ATTRACT
  • Effects of magnetism is very similar to the effects of static electrical charges.
magnetism from electricity
Magnetism from Electricity
  • Magnets attract only a small group of materials.
    • Iron, nickel, cobalt, steel
  • We can INDUCE magnetism in some materials, especially iron.
  • A wire carrying a current that is coiled around a metal core strengthens the magnetic field.
  • The more coils, the STRONGER the magnetic field (lab!)
  • Electromagnets = magnets created by use of electric current.

Li nk

electricity from magnetism
Electricity from Magnetism
  • Does this work the other way around?
  • YES! If a magnet is moved through a coil of wire, a current is produced in the wire.
  • pHet Faraday interactive
slide30
What did you notice about the current flow?
  • The current only flows when the magnet is moving! When the magnet stops moving, so does the current.
    • The magnet PULLS the electrons along through the wire.
    • The more quickly the magnet moves, the faster the electrons move, SO….more current.
    • Remember… current is more electrons per second
      • More work is being done!
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