Basic Electronics Ninth Edition Basic Electronics Ninth Edition ©2003 The McGraw-Hill Companies Grob Schultz

Basic Electronics Ninth Edition Basic Electronics Ninth Edition ©2003 The McGraw-Hill Companies Electricity 1 CHAPTER

 Negative and Positive Polarities  Electrons and Protons  Structure of the Atom  The Coulomb  The Volt Unit  Electrical Current Topics Covered in Chapter 1

(continued)  Resistance  Closed Circuit  Direction of Current  DC and AC  Sources of Electricity

Positive and Negative Polarities + - Symbol

Electrons and Protons Electricity is present in all forms of matter as electrons and protons. The electron is the basic unit of negative electricity.

The proton is the basic unit of positive electricity. 1 coulomb is equal to 6.25  electrons or protons. Electrons and Protons (continued)

One Atom of Hydrogen Proton Electron The nucleus is made up of a single proton. Only hydrogen has no neutrons (neutral particles) in its nucleus.

One Atom of Copper K K = 2 (complete) L L = 8 (complete) M M = 18 (complete) N = 1 (incomplete) N

Electrical Charges Charges of the same polarity tend to repel one another. Charges of opposite polarity tend to attract one another. Electrons tend to move toward protons because electrons have far less mass than protons.

Unlike charges attract.

Like charges repel.

Types of Electrical Charges Positive charges  Protons  Positive ions  Hole charges Negative charges  Electrons  Negative ions

Atomic Number The atomic number of an element is the number of protons in the nucleus of its atom. The number of electrons in orbit around the nucleus of a neutral atom is equal to the number of protons in the nucleus.

Valence The valence of an element is the number of electrons in the outermost orbit.

29 protons atomic number = electrons (net charge = 0) 1 valence electron The valence electron is weakly bound to the nucleus. This makes copper an excellent conductor.

A coulomb is 6.25 x electrons. An ampere is 1 coulomb of flow per second. The copper valence electrons are easy to move and copper is the most widely applied electrical conductor. A section of current carrying wire

The volt is the unit of potential difference. Potential difference is the amount of energy or work assigned to each coulomb. 1 Volt = 1 Joule 1 coulomb 9 Joules coulomb There are always 2 points involved when discussing potential difference or voltage. 1 2

Resistance is the opposition to electric flow. Resistor  Schematic symbol  The letter symbol is R.  The unit of resistance is the Ohm The symbol is . A component manufactured to have resistance is called a resistor. Conductors like copper have little resistance.

Electric Circuits An electric circuit is a path for electron flow. Potential difference must be applied to a circuit to produce electron current flow. Electrons flow through an external circuit from negative to positive.

Electric Circuits (continued) Direct current (dc) flows in one direction. Alternating current (ac) periodically reverses direction.

A Closed Circuit (current is flowing) The purpose of the resistor is to limit current (flow) or to generate heat.

An Open Circuit (no current is flowing)

The electron current is from negative to positive.

+ - 0 Direct Current (DC) and Alternating Current (AC) time DC AC

Sources of Electricity Static electricity by friction Conversion of chemical energy Electromagnetism Photo electricity Thermal emission