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Principles & Applications
Electricity Principles & Applications Sixth Edition Richard J. Fowler Chapter 2 Electrical Quantities and Units © Glencoe/McGraw-Hill
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INTRODUCTION • Charge »»» Coulomb • Current »»» Ampere
• Voltage »»» Volt • Resistance »»» Ohm • Power »»» Watt
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Electric Charge Electric Charge
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Electric charge is a property possessed by both electrons and protons.
Quantity is CHARGE (Q) Base Unit is COULOMB (C) Examples of correct usage: Charge = 15 Coulombs Q = 15 C
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Current
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Current is the movement of charge in a specified direction.
Illustrations of current in a solid and a liquid follow:
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When an electron enters the + charge area,
_ Ion - - ++ - - - ++ ++ - - ++ - - - - - - ++ ++ ++ - - - - - ++ ++ Ion - - Ion When an electron enters the + charge area, an electron must leave the - charge area.
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An electron moves from ion to ion.
_ Ion - Ion - ++ - - ++ ++ - - ++ - - - - - ++ ++ ++ - - - - ++ ++ Ion - - Ion Ion An electron moves from ion to ion.
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An electron moves from ion to ion.
_ Ion - Ion - ++ - ++ ++ - - - ++ - - - - - ++ ++ ++ - - - - ++ ++ Ion - - Ion Ion An electron moves from ion to ion.
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An electron moves from ion to ion.
_ Ion - - ++ - ++ ++ - - ++ - - - - - - ++ ++ ++ - - - - ++ ++ Ion - - Ion Ion An electron moves from ion to ion.
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An electron moves from ion to ion.
_ - Ion - ++ - ++ ++ - - - ++ - - - - - ++ ++ ++ - - - - ++ ++ - - Ion An electron moves from ion to ion.
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An electron moves from ion to ion.
_ - Ion - - ++ ++ ++ - - - ++ - - Ion - - - ++ ++ ++ - - - - ++ ++ Ion Ion - - Ion Ion An electron moves from ion to ion.
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An electron moves from ion to ion.
_ - - Ion - ++ ++ ++ - - - ++ - - - Ion - - ++ ++ ++ - - - - ++ ++ Ion Ion - - Ion Ion An electron moves from ion to ion.
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An electron moves from ion to ion.
_ - - - ++ ++ ++ - - - - ++ - - - Ion - - ++ ++ ++ - - - - ++ ++ Ion Ion - - Ion Ion An electron moves from ion to ion.
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An electron moves from ion to ion.
_ - Ion - - ++ ++ ++ - - - ++ - - Ion - - ++ ++ ++ - - - - - ++ ++ Ion Ion - - Ion Ion An electron moves from ion to ion.
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An electron moves from ion to ion.
_ - Ion - - ++ ++ ++ - - - ++ - - Ion - - ++ ++ ++ - - - - - ++ ++ Ion Ion - - Ion An electron moves from ion to ion.
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An electron moves from ion to ion.
_ - Ion - - ++ ++ ++ - - - ++ - - Ion - - ++ ++ ++ - - - - - ++ ++ Ion - - Ion An electron moves from ion to ion.
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An electron moves from ion to ion.
_ Ion Ion - Ion - ++ - ++ ++ - - ++ - - - - - - ++ ++ ++ - - - - ++ ++ - - Ion Ion Ion An electron moves from ion to ion.
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Current in a Liquid _ + - - - -
Cl - Cl - Cl - Na + Cl - A salt electrolyte contains + sodium ions and - chlorine ions. When the plates are connected to a source of - and + charges, the ions move toward the plate with an opposite charge.
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Electric Current Terminology An ampere equals a coulomb per second.
Quantity is CURRENT (I) Base Unit is AMPERE (A) An ampere equals a coulomb per second. Examples of correct usage: Current = 12 Amperes I = 12 A
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Electric Current Relationships
Charge Q Current = I = t Time Examples: Q 14 C = 1.4 A I = = t 10 s Q 14 C = 10 s t = = I 1.4 A
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Charge and Current Quiz
The base unit of charge is the ____ . coulomb The ____ is the base unit of current. ampere The symbol for current is ____. I The symbol for the coulomb is ____. C Current in a solid causes ____ to move from ion to ion. electrons When Q = 15 C and t = 5 s, the current equals ____. 3 A
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Voltage
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Definition of Voltage Voltage is the electric pressure or force that causes current. It is a potential energy difference between two points. It is also known as an electromotive force (emf).
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A volt equals a joule per coulomb.
Voltage Terminology Quantity is VOLTAGE (V) Base Unit is VOLT (V) A volt equals a joule per coulomb. Examples of correct usage: Voltage = 32 Volts V = 32 V
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Voltage Relationships
Energy W Voltage = V = Q Charge Examples: W 56 J = 28 V V = = Q 2 C W 84 J = 4 C Q = = V 21 V
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Voltage Quiz Electromotive force is another name for ____. voltage
The base unit of voltage is the ____. volt The symbol for voltage is ____. V The symbol for the volt is ____. V A volt is equal to a ____ per ____. joule, coulomb Q = ____ when W = 75 J and V = 15 V. 5 C W = ____ when V = 20 V and Q = 2.5 C. 50 J
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Resistance
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Definition of Resistance
Resistance is the opposition a material offers to current. Resistance is determined by: Type of material (resistivity) Temperature of material Cross-sectional area Length of material
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Some Factors That Determine Resistance
For a specific material and temperature, this block has given amount of resistance. Doubling the length of the block, doubles the resistance. Doubling the cross-sectional area, halves the resistance.
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Resistance Terminology An ohm equals a volt per ampere.
Quantity is RESISTANCE (R) Base Unit is OHM (W) An ohm equals a volt per ampere. Examples of correct usage: Resistance = 47 ohms R = 47 W
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Resistance Relationships
Resistivity x length KL Resistance = R = A area Example: KL 1.4 x10-6 W· cm x 2 x104 cm R = = A 0.28 cm2 = 0.1 W
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Power
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Definition of Power Power is the rate of using energy or doing work.
“Using energy” means that energy is being converted to a different form.
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A watt equals a joule per second.
Power Terminology Quantity is POWER (P) Base Unit is WATT (W) A watt equals a joule per second. Examples of correct usage: Power = 120 Watts P = 120 W
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Power Relationships Energy W Power = P = t Time Examples: W 158 J
W = Pt = 75 W x 25 s = 1875 J
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Resistance and Power Quiz
A material’s opposition to current is called ____. resistance The base unit of resistance is the ____. ohm The symbol for the ohm is ____. W The rate of doing work is called ____. power The base unit of power is the ____. watt The symbol for the watt is ____. W P = ____ when W = 160 J and t = 8 s. 20 W
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Multiple and Submultiple Units
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Base, Sub, and Multiple Units
Conversion Between Base, Sub, and Multiple Units . . 3 . 2 . 1 . 1 . A or 0.3 A To convert 300 mA to A, 300 mA . 2 move the decimal point three places to the left, and change mA to A. 5.200 kJ or 5.2 kJ 2 52.00 J 3 5.200 J 5200. J 1 520.0 J To convert 5200 J to kJ, move the decimal point three places to the left, and change J to kJ. 004.0 V 2 0040. mV or 40 mV 3 0040. V 00.4 V 1 0.04 V To convert 0.04 V to mV, move the decimal point three places to the right. and change V to mV.
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REVIEW Charge »»» Coulomb Current »»» Ampere Voltage »»» Volt
Resistance »»» Ohm Power »»» Watt
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