**Electrical Theory**

Conductor allows electricity to easily flow through it

An insulator does not allow electricity to easily flow through it

Electron theory defines electron flow as motion from negative to positive

Conventional theory of current flow states that current flow from a positive point to a less positive point

Summary

The total amperage is the sum of the current flow through each parallel branch

The total amperage of each parallel branch is determined by the resistance in the branch

Characteristics of a Series-Parallel Circuit (cont’d)

The total resistance is the sum of the resistance value of the parallel portion and the series resistance

The voltage drop over the parallel branch resistance is determined by the resistance value of the series resistor

Characteristics of a Series-Parallel Circuit

The current flow through each leg will be different if the resistances are different

The sum of the current in each leg equals the total current of the parallel circuit

Characteristics of a Parallel Circuit (cont’d)

The voltage applied to each leg is the same

The voltage drop across each parallel leg will be the same (if resistors are the same)

The total resistance will always be less than the smallest resistor

Characteristics of a Parallel Circuit

Electrons flow only when a voltage difference exists between two points in a conductor

Current flows to ground in an electrical circuit

Ground is defined as the common negative connection of the electrical system and is the point of lowest voltage

Laws That Regulate Current Flow (cont’d)

Electrons repel each other

Like charges repel each other

Unlike charges attract each other

Electrons flow in a conductor only when affected by electromotive force

A voltage difference is created in the conductor when EMF is acting on a conductor

Laws That Regulate Current Flow

Voltage Drop

Voltage always drops as current flows through the resistance

An increase in resistance causes a decrease in current

All resistances change the electrical energy into heat energy to some extent

The Impact of Resistance

on a Circuit

1. The atomic structure of the material

2. The length of the conductor

3. The diameter of the conductor

4. Temperature

5. The physical condition of the conductor

The Five Basic Characteristics That Determine Resistance

It is defined as the opposition to electron flow

It is measured in ohms

An (R) or () is used to designate resistance

Resistance

A semiconductor is neither a good conductor nor a good insulator

Examples of semiconductors

Silicon

Germanium

Carbon

Semiconductors

An insulator is not capable of supporting the flow of electricity

Examples of good insulators

Rubber

Wood

Ceramics

Most plastics

Insulators

Electricity can be produced by magnetic induction

Mutual induction is used in ignition coils

Self-induction is governed by Lenz’s Law

Magnetic induction is basis for a generator

Theory of Induction

Factors Affecting the Strength of an Electromagnetic Coil

The amount of current flowing through the wire

The number of windings or turns

The size, length, and type of core material

The direction of the magnetic field at which the lines of force are cut

When current flows through a conductor, a magnetic field is formed around the conductor

When a conductor is passed through a magnetic field, electrons will flow in the conductor

Electricity and Magnetism

Uses the theory of capacitance to temporarily store electrical energy

Common uses

Control voltage spikes

Reduce radio noise

Store reserve energy

Capacitance

Characteristics of a Series-Parallel Circuit (cont’d)

Characteristics of a Parallel Circuit (cont’d)

Characteristics of a Series Circuit

The total resistance is equal to the sum of all the resistances

The current is the same at all points of the circuit

The voltage drop across each resistor will be different if the resistor values are different

The sum of the voltage drop of each resistor equals the source voltage

Characteristics of a Series Circuit

Battery

Power source

Wires

Conductors

Load

Light, motor, etc.

Components of an

Electrical Circuit

1 Watt = 1 Volt x 1 Ampere

The formula can be expressed as

P (power) = E (volts) x I (amps)

E (volts) = P (power) / I (amps)

I (amps) = P (power) / E (volts)

Watts is a measurement of power

Watt’s Law Formula

1 Volt = 1 Ampere x 1 Ohm

The formula can be expressed as

E (volts) = I (amps) x R (resistance)

R (resistance) = E (volts) / I (amps)

I (amps) = E (volts) / R (resistance)

Ohm’s Law Formula

It is defined as the rate of flow of electrons

It is the measurement of the number of electrons passing a given point in a circuit in one second

It is measured in amperes (amps)

An (A) or (I) is used to designate amperage

Current

It is the electrical pressure that causes electron movement in a circuit

It is referred to as electromotive force (EMF)

It is measured in volts

An (E) or (V) is used to designate voltage

Voltage

A conductor supports the flow of electricity through it

Examples of good conductors:

Copper

Gold

Aluminum

Steel

Conductors

Kirchhoff’s Current Law states the algebraic sum of currents entering and leaving must equal zero

Kirchhoff’s Voltage Law states the algebraic sum of voltage sources and drops must equal zero

Kirchhoff’s Laws

Direct Current (DC)

Is produced by a battery

Current flows in one direction

Alternating Current (AC)

Is produced any time a conductor moves through a magnetic field

Current changes directions from positive to negative

Types of Current

Electricity

The flow of electrons through a conductor

Electron theory

Defines the flow of electrons from negative to positive

Conventional theory

States that current flows from a positive point to a less positive point

Electrical Definitions

**TAKE NOTES!**

Conductor

wood

rubber

silicon

ATOMIC STRUCTURE

Atoms try to balance electrons to protons

Protons: positive charge

Electrons: negative charge

Neutrons: neutral

Valance Ring

1 to 3 electrons

in valance ring

Allows for electrons to move

5 to 8 electrons

in valence ring

Does not allow electrons to move

3 or less=conductor

5 or more= insulator

4= semi-conductor

Electricity=Energy

Energy cannot be created or destroyed

...but it can be changed

heat

light

Motion

I (Intesity) E(Electromotive Force)

Open circuit?

Closed circuit?

A. 2 ohm resistor

Voltage = 12 volts

Amperage= ?

Ohms law A=V / R

(I=E / R)

A=12 / 2

A=? V=?

B. 2 ohm + 4 ohm = ?

Voltage = 12 volts

Amperage = ?

Ohms law A= V / R

(I= E / R)

A=? V=?

So the entire circuit as how much amperage?

What is the voltage drop?

Use Ohm's law

Series

Parallel

The voltage applied to each leg is the same

The voltage drop across each parallel leg will be the same (if resistors are the same)

The total resistance will always be less than the smallest resistor

The current flow through each leg will be different if the resistances are different

The sum of the current in each leg equals the total current of the parallel circuit

Resistance?

This is a little harder to figure out!

How do you figure out resistance in a parallel circuit?

Total resistance is always less than the lowest individual resistance

because current has more than one path to follow

One path

Method to find resistance depend on:

How many parallel branches

Resistance of each branch

And you? Your personal preferences

Several methods are used. Use the one that feels the best to you.

If all resistances in each leg are equal:

R

T

=

Value of one resistor

Total number of branches

resistance in each leg = 6 ohms

total branches = 3 branches

R

T

=

6 ohm / 3 branches

R

T

=

2 ohms

resistance in each leg = 6 ohms

total branches = 2 branches

R

T

=

6 ohms / 2 branches

R

T

=

3 ohms

Note amperage

As resistance goes down...

Amperage goes up!

Another way to figure out total resistance

Try this:

R

T

=

R

1

X

R

2

R

1

+

R

2

with only 2 legs

R

T

=

6 ohms x 6 ohms

6 ohms + 6 ohms

R

T

=

36 ohms

12 ohms

=

3 ohms

Amperage?

Voltage drop?

On each leg?

12 volts

2 amps each leg

4 amps total

Each branch calculated separately

But what if we have more than 2 branches?

R

T

=

1

R

1

+

R

2

+

R

3

...

R

n

1

1

1

1

R

T

=

1

1

6

+

1

6

+

1

6

R

T

=

1

3

6

=

1

1

2

This means we take the reciprocal

(turn it upside down)

R

T

=

1

x

2

1

=

2 ohms

Reciprocal = reverse numerator and denominator

Numerator

Denominator

x

y

becomes

y

x

To add fractions, must have

like denominators

Seek common denominators

Even another way

It could be easier to find current in each leg, then use ohms law to calculate total resistance

Current in each leg:

I = E / R

I = 12 volts / 6 ohms

I = 2 amps

Branch 1 = 2 amps

Branch 2 = 2 amps

Branch 3 = 2 amps

Total current =

6 amps

add current in each leg

Now find total resistance

R = E / I

R = 12 volts / 6 amps

R = 2 ohms

Let's try 4, 6, and 8 ohms

Let's try 4, 6, and 8 ohms

Let's look back and make sure it's clear for you.

Series Circuits

Each component dependent on others

One path for all current

Add all resistors for Total Resistance

Example

R

1

=

2 ohms

R

2

=

2 ohms

R

3

=

2 ohms

E= 12 volts

I= ?

First, figure out total resistance

2 ohm + 2 ohm + 2ohm = 6 ohms Total Resistance

Next use ohms law to find current

12 volts / 6 ohms = 2 amps

Current the same all through circuit

Voltage drop:

Use ohms law, individual resistance and current to find voltage

2 amps x 2 ohms = 4 volts

Add all voltage drops and it should equal source voltage

4 volts + 4 volts +4 volts = 12 volts

P

I

E

Watts

12 volts x 2 amps=24 watts

Series circuit

What happens to watts when we change resistance?

Ohms law

Watts law

Let's compute with real numbers

Parallel circuits

All branches have their own B+ and Ground

Current is different in each leg

Total resistance is less than the lowest resistor

Full current pushes through each resistor

If only 1 resistance in a branch, full voltage drop through that resistance

If a short to ground occurred on one leg resistance would go to 0 causing total voltage drop through path of least resistance (0 ohms), and no current flow.

The sum of all the currents in each leg = total current

MUST FIND TOTAL RESISTANCE TO FIND TOTAL CURRENT

Parallel circuits

Formulas

for finding total resistance

If all resistors are equal:

R = value of one resistor / total number of branches

T

If you have 2 paths for current flow:

R = (R x R ) / (R +R )

T

1

2

1

2

If more than 2 legs:

R =

T

1

1

__

R

+

1

__

R

+

1

__

R

1

2

3

...

1

__

n

R

Then take the reciprocate. Whatever is the bottom number is the total resistance.

Or figure out total current:

Find out the current in each branch and add them together for total current.

Then use ohm's law to find total resistance using the total current you just found.

Calculate series side first

What is the resistance on the series side?

10 ohms!

What is the resistance of the parallel side?

R = (R x R ) / (R + R )

T

1

2

1

2

(4 x 4) / (4 + 4) = 16 / 8 =

=

2 ohms!

Now add them up!

10 ohms + 2 ohms = 12 ohms total resistance

Now find total current:

I = E/R

I= 12 / 12

I= 1 amp

Current of each parallel leg comes is calculated from the resistance in that leg

and voltage drop on each leg

Now find the voltage drops

Total voltage drop for the whole circuit has to be 12 volts

Some voltage dropped by the parallel side and some on the series side

We know:

Circuit current is 1 amp

Parallel resistance value is 2 ohms

Series resistance value is 10 ohms

Total voltage drop is 12 volts

Lets figure out voltage drop on parallel side

E= I x R E = 1 x 2 E = 2 volts!

So 2 volts dropped by each 4 ohm resistor!

Now current through each leg

I = E / R I = 2 / 4 I = 0.5 amps!

So each leg has 0.5 amps. Total current is 1 amp. Do our numbers add up?

4 electrons in the valence makes it happy

Very strong bonds

Nothing to share...but...

By doping it becomes tweaked!

N type doping = imperfections by adding Arsenic or Phosphorus giving it an extra electron that wants to go somewhere ... POOF a negative charge and it is a conductor!

Form perfect lattices

OR

P type doping = imperfections by adding Boron or Gallium that makes it missing an electron causing a hole...POOF a positive charge and it is a conductor!

Almost an insulator

A good conductor but not a great one!

Diodes

Transistors

Micro Processors