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4.16 Electrical Theory

This presentation is a deeper look at the theories that rule electrical operation
by

Ivan W. Anderson

on 8 July 2014

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Transcript of 4.16 Electrical Theory

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
Full transcript