Resistance is measured in ohms

Scientific notation - is a means of using single-digit numbers plus powers of 10 to express large and small
numbers
- expresses very large and small numbers in a form of mathematical shorthand.
Voltage source - he device that supplies electrons from one end of a conductor (the negative terminal)
and removes them from the other end of the conductor (the positive terminal).
- can be considered a pump that supplies electrons to the load and recycles the excess electrons
Hole - As electrons move from one atom to another, they create the appearance of a positive charge.
- movement (positive charge) occurs in the opposite direction to electron movement.
An electric current (i) consists of the drift of electrons from an area of negative charge to an area of
positive charge.
The unit of measurement for current flow is the ampere (A).
An ampere represents the amount of current in a conductor when 1 coulomb of charge moves past a
point in 1 second. The relationship between amperes and coulombs per second can be expressed as
follows
Repelling - is a movement when two electrons together or two protons together represent “like”
charges. Like charges resist being brought together and instead move away from each other.
Charles Coulomb - name by The unit adopted for measuring charges is the coulomb (C),
I = current measured in amperes
Q = quantity of electrical charge in coulombs
t = time in seconds

Electrical charges are created by the displacement of electrons.

The atom - has been defined as the smallest particle of an element.

Current – the flow of electrons when a difference of potential exists between two charged bodies
connected by a conductor, electrons will flow along the conductor
Electrical charge (Q) is measured in coulombs (C).
Laws of electrostatic charges: Like charges repel; unlike charges attract.
The prefix milli- means one-thousandth.
The prefix micro- means one-millionth.
Electrons - travel very slowly through a conductor, but individual electrons move at the speed of light.
One coulomb is equal to 6.24x1018 electrons.

Difference of potential, or voltage - The force that causes the electrons to move in a common direction
A Van de Graaf generator is capable of producing millions of volts.
A current is produced when an electron is forced from its orbit around an atom
The six most common voltage sources are friction, magnetism, chemicals, light, heat, and pressure.
direct current (Dc).When electrons flow in only one direction
alternating current (ac) - When electrons flow in one direction and then in the opposite direction
A generator uses magnetism to produce electricity
consists of two dissimilar metals, copper and zinc, immersed in a salt, acid, or alkaline solution
Light energy can be converted directly to electrical energy by light striking a photosensitive ( light-
sensitive) substance in a photovoltaic cell (solar cell)
A solar cell consists of photosensitive materials mounted between metal contacts.
thermocouple - Heat can be converted directly to electricity with a device
- A thermocouple consists of two dissimilar metal wires twisted together. One wire is copper and the
other wire is zinc or iron.
the combination of two or more cells forms a battery
When pressure is applied to certain crystalline materials such as quartz, tourmaline, Rochelle salts, or
barium titanate, a small voltage is produced. This is referred to as the piezoelectric effect
Uses of the piezoelectric effect include crystal microphones, phonograph pickups (crystal cartridges), and
precision oscillators.
There are two basic types of cells
cannot be recharged are called primary cells.
Cells that can be recharged are called secondary cells.
An example of a primary cell is a Leclanche cell, also called a dry cell (Figure 12-12).
The alkaline cell is named because of the highly caustic base, potassium hydroxide (KOH), used as the
electrolyte.
lithium cells (Figure 12-15) have overcome the inherent properties associated with lithium. Lithium is
extremely reactive with water.
Another type of secondary cell is the nickel cadmium (ni-cad) cell (Figure 12-17). This is a dry cell that
can be recharged many times and can hold its charge for long periods of time.

Cells and batteries can be connected together to increase voltage and/or current. They can be connected
in series, in parallel, or in series-parallel. In series, cells or batteries can be connected in either series-
aiding or series-opposing

In a series-aiding configuration, the positive terminal of the first cell is connected to the negative
terminal of the second cell;
In a series-opposing configuration, the cells or batteries are connected with like terminals together,
negative to negative or positive to positive.
In a parallel configuration, all the positive terminals are connected together and all the negative
terminals are connected together (Figure 12-19).
A potential applied to a circuit is a called a voltage rise.
A voltage drop occurs when there is a current flow in the circuit
- the energy used by the circuit in a passing current through the load (resistance)
Ground is a term used to identify zero potential. All other potentials are either positive or negative with
respect to ground. There are two types of grounds: earth and electrical.
Earth grounding is used to prevent electric shock by keeping all appliances and equipment at the same
potential.
Electrical grounding provides a common reference point.
Magnetism is the most common method used to produce a voltage.
Chemical cells are the second most common means of producing a voltage
A voltage source provides a means of converting some other form of energy into electrical energy.
Lead-acid batteries and nickel-cadmium (Ni-Cad) cells are examples of secondary cells
Current is produced when an electron is forced from its orbit.
Voltage provides the energy to dislodge electrons from their orbit.
Voltage applied to a circuit is referred to as a voltage rise.
The energy used by a circuit is referred to as a voltage drop.
A series-parallel combination increases both the output voltage and the output current.

Matter - is anything that occupies space and has weight.

Element - is the basic building block of nature.
Compound - The chemical combination of two or more elements
Molecule - The smallest part of the compound that still retains the properties of the compound
- the chemical combination of two or more atoms.
Mixture - The physical combination of elements and compounds
Nucleus - is located at the center of the atom.
Protons - It contains positively charged particles
Neutrons - uncharged particles (neutral)
Electrons - Negatively charged particles
Atomic number - The number of protons in the nucleus of the atom
Atomic weight - the mass of the atom and is determined by the total number of protons and neutrons
in the nucleus
Shell - Each orbit
Valence shell - The outer shell
Valence - the number of electrons it contains
Conductors - Materials that contain a large number of free electrons
Insulators - the opposite of conductors, prevent the flow of electricity
Semiconductors - Halfway between conductors and insulators
Electrically balanced atom - An atom that has the same number of electrons and protons
Negative Ion - It is said to be negatively charged
Positive ion - A balanced atom that loses one or more electrons is said to be positively charged
Ionization - The process of gaining or losing electrons
Ω - The Greek letter omega (Ω) is used to represent ohms.
The charge of 6,240,000,000,000,000,000 (or 6.2431018) electrons is called a coulomb.

Resistors are either fixed or variable

The tolerance of a resistor is the amount that its resistance can vary and still be acceptable.
Resistors are either carbon composition, wirewound, or film.
Carbon composition resistors were the most commonly used resistors.
Wirewound resistors are used in high-current circuits that must dissipate large amounts of heat
Film resistors offer small size with high accuracy.
Variable resistors used to control voltage are called potentiometers.
Variable resistors used to control current are called rheostats.
Resistor values may be identified by colored bands:
The first band represents the first digit.
The second band represents the second digit.
The third band represents the number of zeros to be added to the first two digits.
The fourth band represents the tolerance.
A fifth band may be added to represent reliability.
The path that the current follows is called an electric circuit.
The load consists of some type of resistance to current flow
A series circuit offers a single path for current flow.
A parallel circuit offers more than one path for current flow.
A series-parallel circuit is a combination of a series circuit and a parallel circuit.
Current flow in an electric circuit flows from the negative side of the voltage source, through the load,
and returns to the voltage source through the positive terminal.

George Ohm first observed

Ohm’s law, or the relationship among current, voltage, and resistance.
Ohm’s law states that the current in an electric circuit is directly proportional to the voltage and
inversely proportional to the resistance in a circuit.
I = current in amperes
E = voltage in volts
R = resistance in ohms

In 1847, G. R. Kirchhoff extended Ohm’s law with two important statements that are referred to as
Kirchhoff ’s laws.
The first law, known as Kirchhoff’s current law.
Kirchhoff ’s second law is referred to as Kirchhoff’s voltage law

I = E/R - formula of Ohm's Law