Outline of Electricity and Magnetism

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Outline of Electricity and Magnetism
11. Electric Power 12. Magnets 13. Magnetic
Field 14. Oersted's Experiment 15.
Electromagnets 16. Magnetic Force on a Current
17. Electric Motors and Generators
18. Electromagnetic Induction 19. Transformers
1. Positive and Negative Charge 2. What is
Charge? 3. Coulombs Law 4. Force on an
Uncharged Object 5. Matter in Bulk 6.
Conductors and Insulators 7. Superconductivity
8. The Ampere 9. Potential Difference 10.
Ohm's Law
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1. Positive and Negative Charge
Opposites attract-Same charges repel Lets try
it!
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1. Positive and Negative Charge
Electrons are stripped from one component and
transferred to the other to cause both to be
oppositely charged.
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Fig. 1.
Ben Franklin discovered electric charge.
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2. What is Charge?
Atoms are composed of protons (), electrons (-)
and neutrons. The nucleus contains the protons
and neutrons and the electrons surround the
nucleus.
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2. What is Charge?
Protons are much larger than electrons but have
an equal and opposite charge.
The coulomb (C) is the unit of electric
charge. The basic quantity of electric charge (e)
is 1.6 x 10-19 C.
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3. Coulombs Law
Q1Q2
F K -------
R2
Charles Coulomb (1736-1806)
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4. Force on an Uncharged Particle
Initially the paper is uncharged, but the comb
polarizes the charges in the paper.
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5. Matter in Bulk
Coulomb's law resembles the law of gravity
however, gravitational forces are always
attractive, whereas electric forces may be
attractive or repulsive.
Coulombs Law
Q1Q2 F
K ------- R2
Law of Gravity
M1M2
F G ------- R2
Gravitational forces dominate on a cosmic scale
electric forces dominate on an atomic scale.
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6. Conductors and Insulators
A conductor is a substance through which electric
charge flows readily. An insulator is a
substance that strongly resists the flow of
electric charge. Semiconductors are substances
whose electrical conductivity is between that of
conductors and insulators.
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Semiconductors
Transistors are switches that conduct electricity
only when a second source of electricity is
energized.
John Bardeen Nobel Prizes in 1956 and 1972 for
developing the transistor and superconductivity.
A
What a Transistor looks like.
B
C
A current will not flow from A to B unless C is
energized.
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Fig. 2.
Enlargement of 5 mm square computer chip.
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7. Superconductivity
Superconductivity refers to the loss of all
electrical resistance by certain materials at
very low temperatures. Substances that are
superconducting at 150K are now known which is
warmer than liquid nitrogen (77K).
Maglev Train in Japan
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8. The Ampere
The Ampere is a measure of how much electrical
current is flowing and is measured in units of
amps.
QI ---- t
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8. The Ampere
The current varies depending on the force behind
the current and the resistance to flow.
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9. Potential Difference
Alessandro Volta (1745-1827)
Potential difference, or voltage, is the
electrical potential energy per coulomb of charge.
JV ---- C
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Fig. 3. 4.
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10. Ohms Law
André Marie Ampére (1775-1836)
Georg Ohm (1787-1854)
VI ---- R
Resistance is a measure of opposition to the flow
of charge and is measured in ohms (?)
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Fig. 5

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DC Circuit Concept Map
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Parallel and Series Circuits

• The Parallel Circuit
• The Series Circuit
• PhysicsLAB An Introduction to DC Circuits
• Capacitance
• Capacitance of a Capacitor

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Fig. 6.
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11. Electric Power
P IV
The power of an electric current is the rate at
which it does work and is equal to the product of
the current and the voltage of a circuit
The unit of electric power is the watt.The
commercial unit of electric energy is the
kilowatthour (kWh).
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11. Electric Power
Typical Power RatingsAppliance
Power (W) Stove 12,000Clothes
Dryer 5,000Heater 2,000Dishwasher
1,600Photocopier 1,400Iron
1,000Vacuum Cleaner 750Coffee Maker
700Refrigerator 400Portable
Sander 200Fan 150Personal
Computer 150 TV Receiver 120Fax
Transmitter/Receiver 65Charger for
Electric Toothbrush 1
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12. Magnets
Every magnet has a north pole and a south pole.
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13. Magnet Field
How to make a magnet Heat in magnetic field.
Magnetic force lines.
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14. Oersteds Experiment
Hans Christian Oersted (1777-1851)
Hans Christian Oersted discovered in 1820 that an
electric current near a compass causes the
compass needle to be deflected. Oersted's
experiment showed that every electric current has
a magnetic field surrounding it.
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14. Oersteds Experiment
According to the right-hand rule, the electron
current in a wire and the magnetic field it
generates are perpendicular to each other.
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14. Oersteds Experiment
All magnetic fields originate from moving
electric charges. A magnetic field appears only
when relative motion is present between an
electric charge and an observer. Electric and
magnetic fields are different aspects of a single
electromagnetic field.
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15. Electromagnets
An electromagnet consists of an iron core placed
inside a wire coil. The magnetic field strength
of a wire coil carrying an electric current
increases in direct proportion to the number of
turns of the coil.
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15. Electromagnets
An electromagnet can be used to move large
quantities of metal. When the current is on the
magnet will pick up the metal. When you want to
drop it you turn off the power and the
electromagnet is disabled and the metal drops.
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16. Magnetic Force on a Current
A magnetic field exerts a sideways push on an
electric current with the maximum push occurring
when the current is perpendicular to the magnetic
field. Currents exert magnetic forces on each
other. The forces are attractive when parallel
currents are in the same direction and are
repulsive when the parallel currents are in
opposite directions.
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Fig. 7.
The experimental Japanese Maglev train uses
magnetic forces for both support and propulsion.
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How a TV works.
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17. Electric Motors
An electric motor uses the sideways push of a
magnetic field to turn a current-carrying wire
loop. Electric motors use a commutator to change
the direction of the current in the loop.
Alternating current electric motors do not use
commutators.
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How Does A Motor Do Work?
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The Force
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Theory Behind a Working Motor
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The Torque
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The Applications of a Motor
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What about a Generator ?

• The current running through coils of wire would
  produce magnetic field that attracts or opposes
  the existing permanent magnet, which then drives
  the coil of wire to move or rotate.
• Reversely, coils of wire move or rotate in a
  magnetic field would also produce a current.
  This is what a generator does.

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How can Motors and Generators help us?

• With the theory of conservation of energy, we
  know that the energy will not disappear. Rather,
  energy would change from one form to another. In
  our discussion today, we have seen electrical
  energy turn into mechanical energy and also from
  mechanical to electrical.
• Motors would help us to utilize the electrical
  energy that we have to do work through the form
  of mechanical energy.
• Generator does the opposite. It transforms
  mechanical energy into electrical energy.
• Generator is able to provide us with the source
  of electricity when we provide other forms of
  energy or materials that could react to release
  energy.

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How Does a Generator Work
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18. Electromagnetic Induction
The effect of producing an induced current is
known as electromagnetic induction. The direction
of the induced current can be reversed by
reversing the motion of the wire or reversing the
field direction. The strength of the current
depends on the strength of the magnetic field and
the speed of the wire's motion.
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Fig. 8.
Michael Faraday (1791-1867) built the first
electric motor and discovered magnetic induction.
The stationary windings of a large electric
motor. magnetic forces underlie the operation of
such motors.
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Fig. 9.
Sharks navigate with the help of the earths
magnetic field. They detect the field using
electromagnetic induction.
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Alternating and Direct Current
Alternating current (ac) is current that flows in
a back-and-forth manner household current
changes direction 120 times each second (60 Hz).
Direct current (dc) flows in one direction.
The ac generator (or alternator) produces an ac
current and can be modified to produce dc current
by 1. Use of a commutator. 2. Use of a rectifier
which permits current to pass through it in only
one direction.
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19. Transformers
A transformer is a device composed of two
unconnected coils, usually wrapped around a soft
iron core, that can increase or decrease the
voltage of ac current.
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19. Transformers
A transformer is used to step the voltage down
and the power up (PIV) so that we can use it.
Low power is desired for the transport of
electricity long distances to avoid loss of
energy to heat loss.
A moving coil activated by voice vibrations is
used as a microphone. The coil induces a current
in the magnet that can be amplified or recorded.
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19. Transformers
A taperecorder records signals from a microphone
on magnetic tape which then can be run across a
magnet and played back.
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What we discussed about Electricity and Magnetism
11. Electric Power 12. Magnets 13. Magnetic
Field 14. Oersted's Experiment 15.
Electromagnets 16. Magnetic Force on a Current
17. Electric Motors and Generators
18. Electromagnetic Induction 19. Transformers
1. Positive and Negative Charge 2. What is
Charge? 3. Coulombs Law 4. Force on an
Uncharged Object 5. Matter in Bulk 6.
Conductors and Insulators 7. Superconductivity
8. The Ampere 9. Potential Difference 10.
Ohm's Law