Principles & Applications Electricity Principles & Applications Sixth Edition Richard J. Fowler Chapter 2 Electrical Quantities and Units ©2003 Glencoe/McGraw-Hill

INTRODUCTION • Charge »»» Coulomb • Current »»» Ampere • Voltage »»» Volt • Resistance »»» Ohm • Power »»» Watt

Electric Charge Electric Charge

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

Current

Current is the movement of charge in a specified direction. Illustrations of current in a solid and a liquid follow:

When an electron enters the + charge area, _ + + + + + + + + + + + + + + Ion - - ++ - - - ++ ++ - - ++ - - - - - - ++ ++ ++ - - - - - ++ ++ Ion - - Ion When an electron enters the + charge area, an electron must leave the - charge area.

An electron moves from ion to ion. _ + + + + + + + + + + + + + + Ion - Ion - ++ - - ++ ++ - - ++ - - - - - ++ ++ ++ - - - - ++ ++ Ion - - Ion Ion An electron moves from ion to ion.

An electron moves from ion to ion. _ + + + + + + + + + + + + + + Ion - Ion - ++ - ++ ++ - - - ++ - - - - - ++ ++ ++ - - - - ++ ++ Ion - - Ion Ion An electron moves from ion to ion.

An electron moves from ion to ion. _ + + + + + + + + + + + + + + Ion - - ++ - ++ ++ - - ++ - - - - - - ++ ++ ++ - - - - ++ ++ Ion - - Ion Ion An electron moves from ion to ion.

An electron moves from ion to ion. _ + + + + + + + + + + + + + + - Ion - ++ - ++ ++ - - - ++ - - - - - ++ ++ ++ - - - - ++ ++ - - Ion An electron moves from ion to ion.

An electron moves from ion to ion. _ + + + + + + + + + + + + + + - Ion - - ++ ++ ++ - - - ++ - - Ion - - - ++ ++ ++ - - - - ++ ++ Ion Ion - - Ion Ion An electron moves from ion to ion.

An electron moves from ion to ion. _ + + + + + + + + + + + + + + - - Ion - ++ ++ ++ - - - ++ - - - Ion - - ++ ++ ++ - - - - ++ ++ Ion Ion - - Ion Ion An electron moves from ion to ion.

An electron moves from ion to ion. _ + + + + + + + + + + + + + + - - - ++ ++ ++ - - - - ++ - - - Ion - - ++ ++ ++ - - - - ++ ++ Ion Ion - - Ion Ion An electron moves from ion to ion.

An electron moves from ion to ion. _ + + + + + + + + + + + + + + - Ion - - ++ ++ ++ - - - ++ - - Ion - - ++ ++ ++ - - - - - ++ ++ Ion Ion - - Ion Ion An electron moves from ion to ion.

An electron moves from ion to ion. _ + + + + + + + + + + + + + + - Ion - - ++ ++ ++ - - - ++ - - Ion - - ++ ++ ++ - - - - - ++ ++ Ion Ion - - Ion An electron moves from ion to ion.

An electron moves from ion to ion. _ + + + + + + + + + + + + + + - Ion - - ++ ++ ++ - - - ++ - - Ion - - ++ ++ ++ - - - - - ++ ++ Ion - - Ion An electron moves from ion to ion.

An electron moves from ion to ion. _ + + + + + + + + + + + + + + Ion Ion - Ion - ++ - ++ ++ - - ++ - - - - - - ++ ++ ++ - - - - ++ ++ - - Ion Ion Ion An electron moves from ion to ion.

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.

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

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

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

Voltage

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).

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

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

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

Resistance

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

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.

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

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

Power

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.

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

Power Relationships Energy W Power = P = t Time Examples: W 158 J W = Pt = 75 W x 25 s = 1875 J

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

Multiple and Submultiple Units

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.

REVIEW Charge »»» Coulomb Current »»» Ampere Voltage »»» Volt Resistance »»» Ohm Power »»» Watt