CHAPTER 1 ef BY UNI DWM20032

Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011)

Voltage Produced by Light

• A photo – electric effect occurs

when light strikes a photo voltaic
material and causes electrons to be

emitted.

• The result is an electric voltage.

• Complete device operates on the
photoelectric principle is photoelectric
cell.

• Usually used in photo-diodes, photo
transistor, solar cell and silicon cells.

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Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011)

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Explain FIVE (5) steps of the
photoelectric voltage
process produced.

[6 marks]

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Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011)

The process of photo electric voltage
being produced

Light strikes the Dislodge electrons from Photosensitive (light
surface of a their orbits . Occurs sensitive) metal
substance because light has
energy(losing electrons) becomes positively
charged

Photo Electric Electric force is
Voltage created

(Voltage produced)

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Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011)

Voltage Produced by Mechanical
Pressure

• Ionic crystals (quartz, Rochelle salts, and
tourmaline) have an ability to generate a voltage if

stresses applied to their surfaces.

• Crystal of quartz is squeezed, charges of opposite Compression of a crystal
polarity will appear on two opposite surfaces of the
crystal.

• Force is reversed and the crystal is stretched -
charges will again appear (opposite polarity from
those produced by squeezing).

• Crystal is given a vibratory motion - produce a Decompression of a crystal
voltage (reversing polarity between two of its
sides)

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Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011) A crystal microphone converts sound waves
to electrical energy
Voltage Produced by Mechanical
Pressure

1. When a voltage(stress) is applied to the
surfaces, the crystal becomes distorted

2. If a mechanical pressure or force is applied
to the crystal surface, a voltage is
developed

3. The crystal microphone, is a familiar
example of this process

4. Sound waves striking a diaphragm, which is
mechanically linked to the crystal surfaces,
cause distortion in the crystal

5. This develops a voltage across its surfaces
6. Thus sound waves are converted to the

electrical energy.

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Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011)

Voltage Produced by Mechanical
Heat
In 1821, an Estonian physicist
named Thomas Johann Seebeck
discovered that when any conductor
(such as a metal) is subjected to a
thermal gradient, it will generate a
small voltage.

Thermocouples make use of this
so-called Peltier-Seebeck effect.

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Voltage Produced by Mechanical
Heat

Greater power capacities than
crystals, but their capacity is still
very small if compared to some
other sources.

A thermo-electric effect is used
to measure temperature on a
thermocouple instrument of
engines, exhaust gas, oven and
furnaces.

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ELECTRICAL FUNDAMENTALS & ELECTRON THEORY

Thermocouples POSITIVE
Bismuth

Cobalt

Potassium

Nickel

Sodium

Lead

Tin

Copper

Platinum

Silver

Zinc

Cadmium

Arsenic

Iron

Thermocouples measure the temperature difference Red
phosphorus
between two points, not absolute temperature.
Antimony

Tellurium

Selenium

NEGATIVE

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ELECTRICAL FUNDAMENTALS & ELECTRON THEORY

A list of the electrical prefixes

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Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011)

DC Circuits

• Electrical circuits consists of a source of DC
electricity with a conducting wire going from one
of the source terminals to a set of electrical
devices and then back to other terminal in a
complete circuit.

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Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011)

DC Circuits

• DC circuits may be in series, parallel or combination.
• A simple DC circuits can be constructed by connecting a

conducting wires from the positive and negative terminal of the
battery to an electrical device such as a light bulb.

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Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011)

DC Circuits

• The electricity flows in a loop from one end of the CLOSED LOOP CIRCUIT
OPEN LOOP CIRCUIT
battery or source of electricity to the other end in a
circuits.

• A complete path must exist before current can

flow through a circuit.

• A complete circuit is often referred to as a closed
circuit because the power source, conductors

and load form a closed loop.

• Bulb is used as the load. The load offers
resistance to the circuits and limits the amount of

current that can flow.

• If the switch is opened, there is no longer a closed
loop and no current can flow. This is often referred

to as an incomplete or open circuit.

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Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011) V= Voltage (V)
I= Current (A)
Ohm’s Law R- Resistance (Ohm)

The current,I passing through a
conductor from one terminal on the
conductor to another terminal point

on the conductor, is DIRECTLY
PROPORTIONAL to the potential
difference, V (i.e voltage drop or
voltage) across the two terminal

points and INVERSELY
PROPORTIONAL to the resistance,R
of the conductor between the two

terminal point.

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ELECTRICAL FUNDAMENTALS & ELECTRON THEORY

A memory device combining Ohm’s Law and the power formulas

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ELECTRICAL FUNDAMENTALS & ELECTRON THEORY

Ohm’s Law

Example 1:
Assume that a circuit has a resistance of 50 ohms and a current
flow through of it 2 amperes. What is the value of the voltage
connected to this circuit? Then, find power.

Example 2 :

120 Volts power source are connected to a resistance of 30

Ohms. Find the value of current flow through the circuit? Then,
find power.
Example 3:
Assume that a circuit has a voltage of 240 volts and a current
flow of 10 amperes. What is the value of the resistance in the
circuit? Then, find power.

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Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011)

ELECTRICAL FUNDAMENTALS & ELECTRON THEORY

Table of Basic Formulas

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Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011)

ELECTRICAL FUNDAMENTALS & ELECTRON THEORY

Example 1: Example 2:

What is the maximum power rating in Calculate the maximum safe current that
Watts of a resistor which has a voltage can pass through a 1.8KΩ resistor rated at
of 12V across it and a current of 50mA 0.5W.
flowing through it.

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Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011)

Exercise

1. Draw a basic electrical circuit diagram. (3 marks)
2. Describe current (4 marks)
3. What resistance would produce a current of 200 amperes with a potential difference

of 2 000 volts? (3 marks)
4. What is the resistance of a light bulb if a 120-volt potential difference produces a

current of 0.8 amperes? (3marks)
5. A 110 volt wall outlet supplies power to a strobe light with a resistance of 2200 ohms.

How much current is flowing through the strobe light? (3 marks)
6. Resistances of 4 Ω and 12 Ω are connected in parallel across a 9 V battery. Determine

the
(a) equivalent circuit resistance,
(b) the supply current, and
(c) the current in each resistor

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Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011)

Kirchoff’s Law

• Developed by a German physicist named
Gustav R. Kirchoff in 1847.

• Kirchoff stated two laws for dealing with
voltage and current relationship in an electric
circuit.

The algebraic sum of the currents entering and
leaving a point must equal zero.

The algebraic sum of the voltage sources and
voltage drops in a closed circuit must equal zero.

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Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011)

ELECTRICAL FUNDAMENTALS & ELECTRON THEORY

Kirchoff’s Law

Kirchoff’s First Law (Kirchoff’s Current Law)

The algebraic sum of the currents entering and
leaving a point must equal zero.

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Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011)

ELECTRICAL FUNDAMENTALS & ELECTRON THEORY

Kirchoff’s Law

Kirchoff’s Second Law (Kirchoff’s Voltage Law)

 The algebraic sum of the potential differences in a
circuit loop must be zero.

 Potential rises are (+) while potential drops are (-)

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Branch Current Method

• A loop is a complete
current path within a
circuit.

• A node is a point where
two or more components
are connected

• A branch is a path that
connects two nodes

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Branch Current Method & Loop Current Method.

In order to solve problem circuits use both of
Kirchhoff’s laws, but be aware that the arbitrary
application of Kirchhoff's two equation will not
always yield an independent set of equations.
However, the following approach will probably
work:
1.Label the current in each branch, but do not worry
about the direction of the actual current.
2.Use only interior loops and all but one node.
3.Solve the system of algebraic equation.

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Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011)

ELECTRICAL FUNDAMENTALS & ELECTRON THEORY

Loop Current Method

This method is also called the mesh loop method and the independent
current variables are taken to be the circulating current in each of the
interior loops.
• Label interior loop currents on a diagram.
• Obtain expression for the voltage changes around each interior loop
• Solve the system of algebraic.
• Depending on the problem, it may ultimately be necessary to

algebraically sum two loop currents in order to obtain the needed
interior branch current for the final answer.

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ELECTRICAL FUNDAMENTALS & ELECTRON THEORY

Loop Current Method

Example

 First we need to find the current
flowing, but although it is probably
easier to do using Ohm’s Law, let us
do using Kirchhoff’s Voltage Law,
which states that the sum of the
voltages around closed circuit equals
0.

(8 ×I)+(12 ×I)+(16 ×I)-36=0
(36 ×I)-36=0

(36 I)=36(36 I)=36
I =1A

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Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011)

Loop Current Method

2

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Significant of a Supply’s Internal Resistance

• All electrical components have internal
resistance.

• In batteries it is mainly due to the resistance
of the electrolyte, in electrical generators it is
mainly due to the machine windings, and
brushes.

• The voltage across the open-circuited V= E - Ir
terminals of a supply is equal to the emf.
V = Terminal Voltage
• When load is connected to the supply, E= emf
the load currents flow through the internal r = resistance
resistance of the supply and causes an I = current
internal resistance volts drop.

• The on-load terminal voltage V is equal to
the emf minus the internal resistance volts
drop.

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Significant of a Supply’s Internal Resistance

Example :
If the battery was 1.5V and had an internal of 1Ω and was supplying a lamp
which took 0.3A then the internal volt drop would be:

Ir

0.3 X 1 Ω = 0.3V

So the terminal voltage would be:

V= E - Ir

V=1.5V – 0.3V= 1.2V

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8/5/2019

1) Assume that a circuit has a resistance of 50 ohms and
the voltage supply is 10V. What is the value of the
power to this circuit?

2) 120 Volts power source are connected to a
power of 10 Watts. Find the value of
resistance through the circuit?

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Resistor

• Resistor is a two-terminal electronic component which implements electrical
resistance as a circuit element.

• When a voltage V is applied across the terminals of a resistor, a current I will
flow through the resistor in direct proportion to that voltage.

• Resistors determine the flow of current in an electrical circuit. Where there is
high resistance in a circuit the flow of current is small, where the resistance is
low the flow of current is large.

• The most common type of resistor consists of a small ceramic (clay) tube
covered partially by a conducting carbon film. The composition of the carbon
determines how much current can pass through.

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Factors Affecting the Resistance

Material

• A copper wire of a particular diameter offers a lower resistance
to current flow than an aluminium wire of the same diameter.

Length

• The longer the length of a given size of wire, the greater the
resistance. If the same size conductor is doubled in length, the
current flow will be reduced by one-half.

Area of cross section

• The resistance varies inversely with the cross-sectional area of a
conductor. If the cross-sectional area of a conductor is doubled,

the resistance to current flow will be reduced in half

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Cont..Factors Affecting the Resistance

Temperature

• The resistance of pure metals, such as silver, copper and
aluminium increases with increase in temperature.

• They are said to have a positive temperature coefficient.

• The resistance of insulators and semi-conductors and

thermistors decreases with an increase in temperature and are
said to have a negative temperature coefficient.
• Temperature coefficient of Resistance represented by the Greek
letter Gamma (α)

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Specific Resistance

• Specific resistance or resistivity is the resistance in ohms

offered by a unit volume of a substance to the flow of electric
current.

• The conducting ability of a material is often indicated by its

resistivity. Resistivity is the reciprocal of conductivity.

• A substance that has a high resistivity will have a low
conductivity and vice versa.

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Specific Resistance

• The resistance of a conductor of a uniform cross section varies
directly as the product of the length and the specific resistance
of the conductor, and inversely as the cross-sectional area of the
conductor. Expressed as an equation the “R” (resistance in
ohms) of a conductor is:

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EXERCISE 

1) State 4 factors affecting resistance of a wire

(4 Marks)

2) How to bleed off a static charge when the
aircraft is flying?

(1 Marks)

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Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011)

Resistor Marking

• Resistors are marked with a number of colored bands.
• Each color stands for a number.
• Three color bands show the resistors value in ohms and the

fourth shows tolerance.
• Can never be made to a precise value and the tolerance band

(the fourth band) tells us, using a percentage, how close the
resistor is to its coded value.

DDIWDDPWILMPOLMM2O0MA230E2A3N: EE2GLN:IENEGCELTIEENRRCEIITCNERARGILICNIFANUGLANIFIDNRUACNAMRIDAREFACNTMRTMAAELFANSTITNMATLEASNINANTECNE ANCE FOFROTRRTARFINOAIIRNNTIGNRPGAUIPNRUIPNROGPSOPESUOERNOPLONYSLYE ONLY
JPDPA/MDW/TDMPW-02M30-320201/3/TR2P/E0TV1P0/00R1/E/1VRM0E0VA0R0C/H2270N1O8V2017

Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011)

ELECTRICAL FUNDAMENTALS & ELECTRON THEORY

Resistor Marking

Most resistors have 4 bands:
• The first band gives the first digit.
• The second band gives the second digit.
• The third band indicates the number of zeros.
• The fourth band is used to shows the tolerance

(precision) of the resistor.

DIPLOMA ENGINEERING IN AIRCRAFT MAINTENANCE FOR TRFOAIRNTINRGAIPNUINRGPOPSUEROPONSLYE ONLY
DWM 2032: ELECTRICAL FUNDAMENTALS DAM/TDPW-0M3-20013/R2/ETVP0001//1RMEVA0R0C/H2270N1O8V2017

Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011)

RESISTOR COLOR CODING

x100

DIPLOMA ENGINEERING IN AIRCRAFT MAINTENANCE FOR TRFOAIRNTINRGAIPNUINRGPOPSUEROPONSLYE ONLY
DWM 2032: ELECTRICAL FUNDAMENTALS DAM/TDPW-0M3-20013/R2/ETVP0001//1RMEVA0R0C/H2270N1O8V2017

Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011)

DIPLOMA ENGINEERING IN AIRCRAFT MAINTENANCE FOR TRFOAIRNTINRGAIPNUINRGPOPSUEROPONSLYE ONLY 195
DWM 2032: ELECTRICAL FUNDAMENTALS DAM/TDPW-0M3-20013/R2/ETVP0001//1RMEVA0R0C/H2270N1O8V2017

Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011)

•Refer to the Table 1, fill in the blank with the correct values.
[6 marks]

1st Band 2nd Band 3rd Band 4th Band Value % Tolerance

Green Red Brown Gold

Violet 7600Ω 10

Red Green Silver Silver

Grey 6.8MΩ 5

Red Yellow Brown Silver

DIPLOMA ENGINEERING IN AIRCRAFT MAINTENANCE FOR TRFOAIRNTINRGAIPNUINRGPOPSUEROPONSLYE ONLY 196
DWM 2032: ELECTRICAL FUNDAMENTALS DAM/TDPW-0M3-20013/R2/ETVP0001//1RMEVA0R0C/H2270N1O8V2017

Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011)

•Refer to the Table 2, fill in the blank with the correct values.
[6 marks]

1st Band 2nd Band 3rd Band 4th Band Value % Tolerance
Red Yellow Brown Silver 6800Ω 5
Blue 1.8MΩ 10
Green Silver Silver
Brown Grey
Red Brown Gold
Green

DIPLOMA ENGINEERING IN AIRCRAFT MAINTENANCE FOR TRFOAIRNTINRGAIPNUINRGPOPSUEROPONSLYE ONLY 197
DWM 2032: ELECTRICAL FUNDAMENTALS DAM/TDPW-0M3-20013/R2/ETVP0001//1RMEVA0R0C/H2270N1O8V2017

Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011)

DIPLOMA ENGINEERING IN AIRCRAFT MAINTENANCE FOR TRFOAIRNTINRGAIPNUINRGPOPSUEROPONSLYE ONLY 198
DWM 2032: ELECTRICAL FUNDAMENTALS DAM/TDPW-0M3-20013/R2/ETVP0001//1RMEVA0R0C/H2270N1O8V2017

Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011)

DIPLOMA ENGINEERING IN AIRCRAFT MAINTENANCE FOR TRFOAIRNTINRGAIPNUINRGPOPSUEROPONSLYE ONLY 199
DWM 2032: ELECTRICAL FUNDAMENTALS DAM/TDPW-0M3-20013/R2/ETVP0001//1RMEVA0R0C/H2270N1O8V2017

Topic contents refer as in AN1101/Appendix 1/Issues 1 (01 January 2011)

Wattage Ratings

• A rating expressing the

maximum power that a
device can safely handle

continuously.

• If the flow of current
though a resistor
increases, it heats up, and
if the temperature exceeds
a certain critical value, it
can be damaged.

DIPLOMA ENGINEERING IN AIRCRAFT MAINTENANCE FOR TRFOAIRNTINRGAIPNUINRGPOPSUEROPONSLYE ONLY
DWM 2032: ELECTRICAL FUNDAMENTALS DAM/TDPW-0M3-20013/R2/ETVP0001//1RMEVA0R0C/H2270N1O8V2017