ELECTRICITY

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Chapter 8 Electricity and Magnetism
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ELECTRICITY MAGNETISM


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ELECTRIC CHARGE

• A FUNDAMENTAL QUANITY
• A. ELECTRONS - CHARGE
• B. PROTONS CHARGE
• C. NEUTRONS 0 CHARGE
• D. COULOMB UNIT OF ELECTRIC
• CHARGE

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LAW OF CHARGES

• LIKE CHARGES REPEL AND UNLIKE
• CHARGES ATTRACT
• --
• -- --

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Static Electricity
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• Electrostatic Charge.
• Electrons move from atom to atom to create ions.
• positively charges ions result from the loss of
  electrons and are called cations
• Negatively charge ions result from the gain of
  electrons and are called anions

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• The charge on an ion is called an electrostatic
  charge.
• An object becomes electro statically charged by
• Friction ,which transfers electrons between two
  objects in contact
• Contact with a charged body which results in the
  transfer of electrons
• Induction which produces a charge redistribution
  of electrons in a material

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• Electrical Conductors and Insulators.
• Electrical conductors are materials that can move
  electrons easily
• Good conductors include metals.
• Electrical nonconductors are materials that do
  not move electrons easily
• These are also known as insulators
• Semiconductors are materials that vary in their
  conduction and nonconduction, sometimes
  conducting sometimes not conducting.

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• The fundamental charge is the electrical
  charge on an electron and has a magnitude of
  1.6021892 X 10-19 C
• To determine the quantity of an electrical charge
  you simply multiple the number of electrons by
  the fundamental charge on an electron or
• qne
• Where q is the magnitude of the charge, n is the
  number of electrons, and e is the fundamental
  charge.

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• Measuring Electrical Charges.
• The magnitude of an electrical charge is
  dependent upon how many electrons have been
  moved to it or away from it.
• Electrical charge is measured in
  coulombs.
• A coulomb is the charge resulting from the
  transfer of 6.24 X 1018 of the charge
  carried by an electron

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COULOMBS LAW

• THE FORCE OF ATTRACTION OR REPULSION IS DIRECTLY
  PROPORTIONAL TO THE PRODUCT OF THE 2 CHARGES AND
  INVERSELY PROPORTIONAL TO THE SQUARE OF THE
  DISTANCE BETWEEN THEM.
• F K Q1 Q2
  K 9X 10 9
• R2

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ELECTRICITY

• THE EFFECTS OF MOVING CHARGES OR ELECTRONS
• A. VOLTAGE WORK PER UNIT CHARGE OR ELECTRICAL
  POTENTIAL ENERGY DIFFERENCE
• B. V W/q VVOLTAGE
• WWORK (JOULES)
• qCHARGE (COULOMB

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CURRENT

• E. CURRENT- WHEN THE CHARGE FLOWS
• 1. AMPERE (A) 1 COULOMB/SEC
• 2. Iq/t IELECTRIC CURRENT
• q ELECTRIC CHARGE
• tTIME
• qIt
• 1 COULOMB1 AMPERE X 1 SECOND

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Figure 8.5aSimple Electrical Circuit and Water
Analogy
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Figure 8.5bSimple Electrical Circuit and Water
Analogy (continued)
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RESISTANCE

• OPPOSITION TO THE FLOW
• 1. OHMUNIT OF RESISTANCE
• 2. OHMS LAW VIR
• IV/R
• RV/I
• POWERIV PI2R
• IP/V

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EXAMPLE

• WHAT IS THE CURRENT AND RESISTANCE OF A 60 WATT
  BULB PLUGGED INTO A 120 VOLT OUTLET
• IP/V 60 WATTS .5AMPS
• 120 VOLTS
• RV/1 120/.5 240 OHMS

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ELECTRIC CURRENT

• 1. DCDIRECT CURRENT FLOW IN ONE DIRECTION
  (FLASHLIGHT BAT)
• 2. ACALTERNATING CURRENT CHANGES VOLTAGE FROM
  TO -
• IN YOUR HOUSE

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SERIES CIRCUIT

• THE SAME CURRENT FLOWS THROUGH EACH ELEMENT OF
  CIRCUIT
• 1. VIR1 IR2 IR3 .
• VOLTAGE DROPS
• 2. CHRISTMAS TREE LIGHTS
• ONE GOES OUT ALL OUT

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Figure 8.7Series Circuit
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PARALLEL CIRCUITS

• THE CURRENT DIVIDES, SOME GOES TO EACH ELEMENT
• VOLTAGE ACROSS RESISTANCE IS THE SAME
• IV/R V/R V/R
• MOST HOME APPLIANCES

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Figure 8.8Parallel Circuit
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Figure 8.9Household Circuits
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This meter measures the amount of electric work
done in the circuits, usually over a time period
of a month. The work is measured in kWhr
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MAGNETISM

• MOVING AND SPINNING ELECTRONS CAUSE MAGNETISM
• A.. LAW OF POLES- LIKE REPELS
• OPPOSITE ATTRACT

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FERROMAGNETIC

• MATERIALS THAT ARE HIGHLY MAGNETIC
• 1. IRON CURRIE TEMP 770 C
• 2 NICKEL
• 3. COBALT
• ALLOYS CAN BE MAGNETIZED FOR A LONG TIME

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.
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MAGNETIC FIELDS

• IMAGINARY LINES THAT INDICATE THE DIRECTION THAT
  A COMPASS WOULD POINT IF PLACED NEAR A MAGNET.
  MAKE COMPLETE LOOPS THROUGH AND AROUND

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Magnetic field
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Figure 8.23Magnetic Deflection
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ELECTRIC FIELDS

• IMAGINARY LINES THAT INDICATE THE DIRECTION A
  SMALL POSITIVE CHARGE WOULD MOVE IF IT WERE
  PLACED IN A PARTICULAR SPOT

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Oersted discovered that a compass needle below a
wire (A) pointed north when there was not a
current, (B) moved at right angles when a current
flowed one way, and (C) moved at right angles in
the opposite direction when the current was
reversed
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MAGNETIC DECLINATION

• VARIATION BETWEEN THE MAGNETIC MERIDIAN AND
  GEOGRAPHIC MERIDIAN
• 1. MAGNETIC POLE IS 13 DEGREES SOUTH OF
  GEOGRAPHIC NORTH POLE
• EARTH IS A LARGE MAGNET (WHY)

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The earth's magnetic field. Note that the
magnetic north pole and the geographic North Pole
are not in the same place. Note also that the
magnetic north pole acts as if the south pole of
a huge bar magnet were inside the earth. You know
that is must be a magnetic south pole since the
north end of a magnetic compass is attracted to
it and opposite poles attract
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ELECTROMAGNETISM

• A MOVING ELECTRIC CHARGES CREATE MAGNETIC
  FIELDS
• B. A MAGNETIC FIELD MAY DEFLECT A MOVING CHARGE
• 1. ELECTROMAGNETS ARE FORMED WHEN A CURRENT
  CARRYING COIL OF INSULATED WIRE IS WRAPPED AROUND
  A PIECE OF SOFT IRON

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MOTORS AND GENERATORS

• MOTOR CONVERTS ELECTRICAL ENERGY INTO MECHANICAL
  ENERGY
• GENERATOR CONVERTS MECHANICAL WORK OR ENERGY INTO
  ELECTRICAL ENERGY

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A schematic of a simple electric motor
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MAGNETIC FORCE

• MAGNETIC FORCE IS PRODUCED ON A MOVING CHARGED
  PARTRICLE DUE TO MAGNETIC FIELD

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Magnetic levitation trains can reach extremely
high speeds. This experimental train in Germany
reaches 435 km/hr (270 mph).
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TRANSFORMER

• A DEVICE WHICH CAN INCREASE OR DECREASE VOLTAGE.
  WORKS ON AC

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(A) This step-down transformer has 10 turns on
the primary for each turn on the secondary and
reduces the voltage from 120 V to 12 V. (B) This
step-up transformer increases the voltage from
120 V to 1,200 V, since there are 10 turns on the
secondary to each turn on the primary
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TRANSFORMER

• INCREASES OR DECREASES VOLTAGE
• V2(N2)(V1) V22ND VOLTAGE
• (N1) V1PRIMARY VOLT
• N1NO. OF TURNS PRIMARY COIL
• N2NO. OF TURNS 2ND COIL

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ELECTRONICS

• BRANCH OF SCIENCE WHICH DEALS WITH THE EMISSION
  AND CONTROL OF ELECTRONS
• CATHODE RAY TUBE--TV
• DIODE -ALLOWS CURRENT TO FLOW
• IN ONLY ONE DIRECTION
• TRANSISTOR AMPLIFIES INPUT
• SIGNAL

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INTEGRATED CIRCUITS

• USING MANY COMPONENTS SUCH AS DIODES, TRANSISTORS
  AND RESISTORS

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ELECTRICAL SAFETY

• 1. FUSE
• 2. CIRCUIT BREAKER
• 3 GROUNDING
• 4 POLARIZED PLUGS

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Figure 8.12aElectrical Safety with Dedicated
Grounding
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Figure 8.12bElectrical Safety with Dedicated
Grounding (continued)
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ELECTRICAL SHOCK

• A. (1 MILLIAMP) CAN BE FELT
• B. (50-100 mA) CAN BE FATAL
• C. (100 mA) IS NEARLY ALWAYS FATAL
• D. AMOUNT OF CURRENT IS DEPENDENT UPON DRYNESS
  OF SKIN
• DRY SKIN500,000 OHMS
• WET SKIN 100 OHMS

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How many electrons make up one coulomb of charge?

• Qne
• Q/en
• E1.6 x 10 -19
• 1/1.6x 10-19 6.25 x 10 18

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An object has one million more electrons than
protons. What is the net charge of the object?

• Qne
• N1 million
• E1.6 x 10-19
• 1 x 10 6) (1.6 x 10 -19)
• 1.6 x 10-13

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There is a net passage of 4.8 x 10 18 electrons
by a point in a wire conductor in .25 sec. What
is the current in the wire?

• I q/t qne
• I ne/t
• 4.8 x 10 18)(1.6 x 10 -19)
• .25
• I3.1 amps

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A current of 1.5 amp flows in a conductor for 6
sec. How much charge passes a given point in the
conductor during this time?

• I 1.5 amp
• T6 sec
• QIT
• Q(1.5)(6)
• Q9 c

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If an electrical component with a resistance of
50 ohms is connected to a 120 volt source, how
much current flows through the component?

• R 50 ohms
• V 120 volts
• IV/R
• I120/50
• I2.4 amps

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A car radio draws .25 amps of current in the
autos 12 volt electrical system.How much
electric power does the radio use?What is the
effective resistance of the radio?

• I.25 amp
• V 12 volts
• P IV (.25)(12) 3 watts
• R V/I (12)/(.25) 48 ohms

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How much does it cost to run a 1500 watt hair
dryer 30 minutes each day for one month (30 days)
at a cost of 8 cents per kWh.

• 1500 watts1.5 kWh
• 30 min .5 hour
• (1.5)(.5)(30)(.08)1.80

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What are the forces on two charges of .5 C and 2
C if they are separated by a distance of 3.0m?

• Q1.5
• Q22 C
• R 3m
• Fk q1 q2 / r2
• F(9 x 109)(.5)(2) / 9
• F1 x 109 repulsive

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A transformer with 1000 turns in the primary coil
has to decrease the voltage from 4400 V to 220 V
for home use. How many turns should there be on
the secondary coil/

• N11000
• V14400
• V2220
• V2n2 (V1)
• n1
• 2200n2 (4400)50 turns
• 1000