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Electricity and Magnetism

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Title: Chapter 21: Electricity pp. 592-618 Author: CCSD Last modified by: CCSD Created Date: 6/2/2005 3:14:58 PM Document presentation format: On-screen Show (4:3) – PowerPoint PPT presentation

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Title: Electricity and Magnetism


1
Electricity and Magnetism
2
Atomic Review
  • An atom consists of 3 particles
  • Protons-positively charged
  • Neutrons-no charge
  • Electrons-negatively charged

3
What is Electricity?
  • A form of energy caused by moving electrons.

4
How charges act
  • Like charges repel
  • Opposite charges attract.
  • Electrons flow from a negatively charged area to
    a positively charged area.

5
  • Most objects are electrically neutral

6
Static Electricity
  • Static means stuck in one place.
  • Static Electricity that doesnt flow like the
    electricity in your house.
  • It builds up and discharges like when

7
Phenomena
  • Lightning strikes
  • You slide across a car seat and touch the door
    handle.
  • Ben Franklin and his kite.
  • Sliding your feet on a rug and touching the
    doorknob.
  • Rubbing a balloon on your hair and sticking it to
    the wall

8
How are charges transferred?
9
  • 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.

10
This creates IONS which are charged particles.
11
Summary
  • The energy used to rub two things together is the
    energy that gets involved in removing and
    transferring electrons.

12
Electrical Charge
  • Can be Transferred.
  • It cannot be created or destroyed.

13
Conductors
  • A conductor allows charges to flow easily
  • Some conductors are better than others
  • Examples
  • Copper
  • Iron

14
Insulators
  • An insulator prevents electric charges from
    flowing easily
  • Examples
  • Rubber Cork
  • Wood Plastic

15
Electric Current
  • Electric Current is the flow of electrons
    through a conductor
  • There are two types of electric current
  • Alternating Current
  • Direct Current

16
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

17
Direct Current
  • Always flows in one direction
  • Always flows from negative to positive
  • Example
  • Battery
  • Creates a lot of heat

18
What is a Battery?
  • A series of electrochemical cells
  • Two types
  • A wet cell
  • A dry cell

19
Wet cell
  • Electrolyte (a conducting material) is a liquid
  • Example
  • Car battery

20
Dry cell
  • Electrolyte is a moist paste
  • Example
  • AA battery

21
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

22
Diagrams
  • Source Resistance
  • Lamp Motor
  • Wire
  • Switch

23
What is a series circuit?
  • A circuit where current follows only one path
  • If one light goes out, the whole circuit goes out

24
Diagram of a Series Circuit
25
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

26
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 parallel
circuit.                                       
                                    
27
What are volts?
  • Electromotive force (EMF) is the force that moves
    electrons in a circuit.
  • A volt is the unit used to measure EMF.

28
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.

29
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.

30
Magnetism
31
Where do magnets come from?
  • Iron can be made into magnets
  • 3 things stick to magnets iron, nickel, cobalt
    (the Iron Triad)

32
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.

33
Magnetism
  • Magnetic
  • Fields

34
Magnetic Fields
  • Exist in regions surrounding magnets.
  • Exerts a torque on a compass needle. (Demo)
  • Compass needles allow us to map out magnetic
    fields.

35
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36
  • Magnetic field lines flow out of the north pole
    and into the south pole.
  • They are continuous and never cross

37
The Earth itself is a magnet!
38
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39
  • Earths magnetic field causes compasses to line
    up.
  • Magnetic north/south pole is about 11º off from
    geographic north/south pole.

40
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.

41
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.

42
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.

43
An electric current produces a magnetic field.
44
the rule of thumb the direction of the current
determines the direction of the magnetic field in
a current carrying wire.
45
Cause
  • All magnetism is caused by the movement of
    charges.

46
Electromagnet
  • An electromagnet is a strong magnet that can be
    turned on and off.

47
Increase strength
  • You can increase the strength of an electromagnet
    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.
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