Oscilloscope

An oscilloscope is a measurement and testing instrument thet measures AC waveforms with two-axis on screen :

1. Vertical Axis

Represent the voltage.

2. Horizontal Axis

Represent the time or phase angle.

The quantities can be shown on the screen of an oscilloscope :

1. Amplitude ( Peak value, Vp).

2. Peak-to-peak value (Vpp).

3. Period (T) and frequency (f).

Example :

From figure as shown below, shows a AC sine wave displayed on the screen of an oscilloscope. The voltage knob is set at 5 v/div. Calculate the Peak-to-peak value (Vpp).

Solution :

Givev:

The variable value (v/div) = 5v/div

The number of vertical division = 6.4 division.

Therefore, peak-to peak value (Vpp) :

Vpp

= 5v/div X 6.4div

= 32V

Vp = Vpp/2 

      =16V

Introduction of Electricity

The Importance And Need For Electricity In Daily Life.

All electrical appliances need electricity in order to function.

Example of electrical appliances :

a) heat energy.

b) sound energy.

c) light energy.

d) mechanical energy.

Electrical Energy Resources :

SEEBECK:

Heat when applied to the tip of two different metal wires will produce a voltage.

PHOTOELECTRIC:

When light is shone onto the surface of selenium, lithium, and semiconductor materials such as silicon, voltage will be generated.

ELECTROMOTIVE:

Current is induced when a  conductor is passed thought a magnetic field.

PIEZOELECTRICITY:

Different strength of pressure exerted on a crystal will generate voltage.

CHEMICAL REACTION:

A chemical reaction between zinc and copper in electrolyte will produce electric charge as in a battery cell.

ELECTROSTATIC FORCE:

Friction between two differenr materials will produce electrostatic force.

Capacitor, C

Capacitor, C

1. Capasitor is a passive component.

2. It can store electric charge in an AC circuit

3. It can be charge and discharge.

Function of capacitor, C :

a) Filter circuit.

1. To reduce ripples or smoothen the wave for a better steady state.

b) Motor circuit.

1. To improve the power factor.

2. To reduce the effect of noise to other equipment when the motor

     is on.

c) Tuned circuit.

1. To determine the frequency of generator and radio frequency.

Capacitance, C

The resistance to change in voltage.

Symbol : C

Unit : Farad

Component : Capacitor

                                       Increasing Voltage                               Decreasing Voltage

                                   Capacitance tries to resist                     Capacitance tries to resist

                                              increment                                             decrement

Average Value & Root Mean Square

Average Value( mean value )

The mean or average value for a complete AC sine wave is zero because of the symmetrical shape of the sine wave.

Positive value = Negative value

Root Mean Square( rms )

The rms is the effective voltage that can generate the same amount of power as a direct current ( DC) that flows through the resistor.

Vrms = (1/√2)X Vp

         = 0.707 X Vp

Frequency, f & Period, T - AC

Frequency, f & Period, T - AC

Example :

From the waferorm shown above :

a) Frequency, f = 2Hz

b) Period, T = 1/f

                       1/2

                        0.5 s (time for one cycle)

Peak value ( Amplitude) Vp :

The maximum current/voltage that can be achieved by an AC sine waveform from zero at vertical axis.

Peak-to-peak value Vpp :

That is measured from the maximum positive voltage to the maximum negative voltage ( or twice its peak value).

Example :

Peak value, Vp = 3V

Peak-to-peak value, Vpp = 3 - (-3) = 6V @

                                Vpp = 2Vp

                                        = 2 X 3V

                                        = 6V

Alternating Current Circuits - (AC)

The Differences Between (AC) & (DC)

a) Direct Current- DC

1. DC is the flow of current in one direction.

2. To generate DC, cell or battery is used.

b) Alternating Current- AC

1. AC is a type of current thet changes its direction constantly according to time.

2. Sine wave as shown below is normally used in power supply.

3. Other AC Waveforms.

Parallel DC Circuit

Parallel DC Circuit

Parallel DC circuit include as many parallel lines as desired.

1. In a parallel circuit, voltage is the same throughout each parallel leg, no matter how many legs are added.

Vs = V1 = V2 = V3

2. Current through a parallel circuit is the sum of the current in each leg.

IT = I1 + I2 + I3

3. Resistance total calculation as follows:

RT = 1 / ( 1/R1 + 1/R2 + 1/R3 )

Example : Parallel DC circuit Analysis :

Current Divider

The current divider is mostly used to determine the current on a parallel resistor circuit with only two brances.

Example :

Formula :

IRX = IT ( RT / RX )

Series DC Circuit

Series DC Circuit

All components of the series circuit are on one line from the power supply and return.

1. The voltage total is equal to the sum of the series voltage drops in the circuit :

Vs = VR1 + VR2 = VR3

2. The same current must flow through all component.

IT = IR1 = IR2 = IR3

3. The resistance total in a series circuit is the sum of the resistance in the circuit.

RT = R1 + R2 + R3....

Example : Series DC Circuit Analysis:

Voltage Divider

1. A voltage divider is used in a circuit where the resistor are connected in a series.

2. The value of the drop voltage can be easily calculated using the voltage divider formula without knowing the

    current.

3. Example :

Ohm's Law

Definition :

Ohm's Law state that the current ( I ) in a direct current electrical circuit is proportional to the voltage ( V ). And inversely proportional to the resistance ( R ). When the temperature is constant.

Appications

Voltage, current and resistance relationship are define by Ohm's Law.

Place finger over letter of unknown,

then known values and their

relationship will be uncovered;

Whenever voltage is supplies to a resistive circuit, the current will flow and generate heat. The heat is power dissipated in the resistor. The symbol is ( P ).

Formula variations of electrical power in relationship to current and voltage;

Quantities And Units (part-2)

c) Voltage (V)

1. Voltage is the potential energy that causes the current to flow in a circuit.

2. This potential energy is produced from a battery or a generator- electromotive fore (emf)

3. The current flows from a higher pressure ( + ) to a lower pressure point ( - ).

4. The unit for the potential difference and emf is volt (V).

5. Formula:

V = I X R

d) Resistance (R)

1. Resistance is a quantity that limit the flow of a current in a circuit.

2. The important characteristic is characteristic is  : low resistance in a circuit allows high current flow, 

    however if the resistance is high the current flow in the circuit will reduced or will become zero.

3. A good conductor = a very low resistance and a good insulator = a very high resistance.

4 Formula

R = V/I

e) Power (P)

1. Power is the rate at which energy is used.

2. A watt is unit for power.

3. Formula :

P = W/T

f) Energy (E)

1. Energy is the capability to do work in a tome.

2. Energy is measured in joule. One joule is equivalent to one watt in one second.

3. Formula :

W = V X I

Direct Current Circuit-(DC)

Direct Current (DC)

Direct Current (DC) is the flow of current in one direction. A basic DC circuit is illustrated as below

Quantities And Units (part-1)

a) Charge (C)

1. Electrical Charge is created when proton and electron charges are separated - it's static.

2. Proton are positively charged particles, while electron are negatively charged particles.

3. Electrical charge is measured in coulomb. One coulomb is the total charge of 6.25 X 10^18 electrons.

Formula :

Q = I X T

b) Current (I)

1. Current is the movement of charge from one point to another in a uni of time.

2. There are two ways of defining the flow of current; first, the conventional current flow and second, the    

    electron current flow. Refers to an illistrated as in figure below;

3. Formula :

I = V/R

Effects Of Electrical Accidents

There are four type of electrical effects:

1. Electrical Shock:

a) 1mA

Mild electric shock.

b) 10mA

Severe electric shock that causes burns and loss of muscles control.

c) 100mA & higher

Electric shock that could be fatal.

2. Burns:

a) First degree burns

sign of redness on the skin can be seen.

b) Second degree burns

Skin to swell and contain liquid.

c) Third degree burns

Reach inside the body and can causes failure of muscular function.

3. Fire

a) Class A fire

Involves organic-based solids such as wood, paper, fabric, and other organic materials

b) Class B fire

involves liquid such as petrol, oil, diesel, turpentine.

c) Class C fire

Caused by gases such as methane and butane.

d) Class D fire

metal-based fire.

4. Explosions

There are several components in the workshop that may explode if they are wrongly connected to power source. A powerful explosion can cause fire.

Important Of Safety

1. Safety precaution is an important aspect in the use of electrical appliances.

2. A safe enviroment is necessary to avoid loss of life and damage to property.

3. Accident result from carelessness, equipment malfaunction and not adhering to safety rules.

Personal Safety

a) Clothing:

1. Wear workshop uniform.

2. Wear insulated,low-heeled shoes.

3. Do not wear any jewellery.

b) Attitude:

1. Report all breakdowns of equipment.

2. Inform the teacher for accident.

3. Plan activities before begin work.

c) Physical condition:

1. Physically fit.

2. Not eye sleepy.

3. Have good eyesight and hearing.

Safety Tool & Equipment

a) Insulation:

Method of protecting, covering and isolating electrical conductors using insulators to prevent the electrical current from flowing.

b) Earthing:

Method of connecting metal parts in an electrical circuit to the ground.

c) Protective device:

A device that reacts by disconnecting the circuit when there is an over flow of current

Safety Workshop & Enviroment

Workshop rules:

1. Ensure workshop has good qeration

2. Ensure workshop has enought lighting.

3. Ensure the workshop heat and clean.

Generation, Transmision, And Distribution Of Electricity

There is two types of electricity generation which are:

a) Direct current generation:

Current that flows through a circuit in one direction is called directed current.

b) Alternating current generation:

Current that is constantly changing its direction of flow, with regards to the polarity of the current source, is called alternating current.

Alternating Current Generation.

there is some types of  power station:

a) Hydro Power Station:

b) Thermal Power Station:

c) Gas Power Station:

Electricity Transmission.

Electricity Distribution.

Consumer Circuit.

Consumer circuit purposes:

a) To ensure the safety of consumers from accidental electric shock.

b) To prevent fire due to electrical faults.

Scematic diagram for a single-phase supply curcuit.