2dix-The Student Choice
Log in Register now

Identification Study & Testing of various electronic components


Aim:- Identification Study & Testing of various electronic components

1. Resistance: - Various types and colour coding.

Resistance is an expression of degree to which electron flow will be impeded through a conductor. The unit is the Ohm. In simple circuits resistance determines the relation between voltage and current. At the extremes a short piece of wire will have a resistance of nearly zero Ohms. While an air gap (for example an open switch) has very large resistance. Intuitively a couple of relationships will hold in conductor, a voltage difference between the two ends will cause a current to flow. How much current will be determined by how much resistance the conductor offers. If there’s less resistance more current will flow. In fact, given a power source of high enough density, if you half the resistance, you will double the current. If you double the resistance, you will half the current.

Resistor: - Components that resists the flow of electricity equally in both directions. The two main important values associated with resistors are their resistance and their power rating. Resistance is measured in Ohms. An Ohm is quite a small measurement for a lot of electrical applications, so the KILO OHM is often used. 1 K Ohm is equal to 1000 Ohm. The other value is power.

Resistors are electronic components which resist the flow of electric current. The higher the value of resistance the lower the current will be. This was discovered by Mr. Ohm.

The simplest resistors are made from carbon rod with end caps and wire leads. Other types are carbon film which is a thin layer of carbon rod. And metal oxide and metal glaze on glass rods.

Variable resistors are available. These can be operated by means of a knob on the control panel.

Examples are volume and brightness controls.

Preset variable resistors are internal controls which are adjusted in value by means of a screw driver. Once adjusted, they are never touched again.

The Resistor colour code: - Ignore the colour of the resistor body. Most resistors have three colored bands close together at one end single band at the other. The three adjacent bands give the resistor value.

The band nearest the wire lead gives the value of the first digit. E.g. Brown=1.


The next band gives the value of the next digit. E.g. red=2.

The third band gives the number of zeros which follows the two digits. E.g. orange=3


Therefore a resister with brown, red, orange bands would have a value of 12000 Ohms. A green, blue, black resistor would be 56 Ohm. (Black indicates that there are no zeros.)


Colour of band

Value of resistance






















If the third band is silver then divide the value of the first two digits by 100. If gold divide by 10.

Example red violet gold is 2.7 Ohms.

The fourth band indicates the tolerance.

Example brown indicates plus or minus 1%.

A 100 Ohm 1% resistor can be in value between 99 Ohm and 101 Ohm.

Colour of band

% Tolerance









Note:-if there is a fifth band with pink colour it indicates a high stability resistor.

2. Capacitor-Various types Coding:-

Capacitor: - Device that temporarily stores electric charge. There are two main important values that characterize a capacitor. The first is the capacitance –measured in Farads. It turns out that a Farad is a huge amount, so capacitors are often measured in micro-Farads or Pico-Farads (pF). The other important quantity is the rated voltage. This value must never be exceeded in a circuit.


The capacitor colour code:-

Some values are indicated with a colour code similar to resistors. There can be some confusion. A 2200pF capacitor will have three red bands. These merge into one wide red band.



Figure: - 1.1 Capacitor colour code

Some values are marked in Pico-Farads using digit numbers. The first two digits are the base number & the third digit is a multiplier.

For example, 102 is 1000 pF and 104 is 100,000pF, 100nF=0.14 F

To find the total values of capacitors in parallel (that is connected across each other) their values are added.


To find the total value if they are in series (that is in line with each other) then the following formula is used.

1/c total = 1/c1 +1/c2 +1/c3 etc.

Variable capacitors are available in which the value can be adjusted by controlling the amount of overlap of the plates or the distance between them. There is a type of diode called the VARICAP DIODE which similar characteristics.


Inductors are coil of wire. They may be wound on tubular FROMERS or may be self supporting. The former may contain a metallic core up its centre. Iron cores are used for frequencies below about 100 kHz. Ferrite cores are used for frequencies up to say 10 MHz Above 100 MHz the cores is usually air and the coil is self-supporting.

At low frequencies the inductor may have hundreds of turns. Above 1 MHz only a few turns.

Most inductors have a low DC resistance since they are wound from copper wire. Inductor values of INDUCTANCE are measured in HENRIES. Inductors oppose the flow of ac current. This opposition is called INDUCTIVE RESISTANCE.

Resistance increases with frequency and as the value of the inductance increases.

A coil of wire which creates a magnetic field when Current passes through it. It may have an iron ore

Inside the coil. It can be used as a transducer Converting electrical energy to mechanical energy by

Pulling on something.



Figure:-1.2, Inductor circuit symbols

4. Diode: - Semiconductor device that conducts electricity in only one direction. Exist in different varieties. Zener diodes permit conduction in the reverse direction only when the reverse voltage exceeds a certain amount. TVS diodes are like Zeners except capable of much higher currents.


5. Transistors: - A transistor is a semiconductor device used to amplify and switch electronic signals and electrical power.


6. Silicon controlled rectifier (SCRs):-


Figure 1.3, SCR

SILICON-CONTROLLED RECTIFIER (SCR) many naval electronic equipment use silicon-controlled rectifiers for the control of power. Like other solid-state components SCRs are subject to failure. You can test most SCRs with a standard ohm-meter, but you must understand just how the SCR functions. SCR is a three element, solid state device in which the forward resistance can be controlled. The three active elements shown in the figure are the anode, cathode, and gate. Although they may differ in outward appearance, all SCRs operate in same way. The SCR acts as like a very high resistance rectifier in both forward and reverse directions without requiring a gate signal. However, when the correct gate signal is applied, the SCR conducts only in the forward direction, the same as any conventional rectifier.




Figure:-1.4, Physical diagram, Equivalent schematic & schematic symbol of SCR

Silicon controlled rectifiers (SCR) are four layer (P-N-P-N) thyristor with in input control terminal (gate). An output terminal (anode) and a terminal common to both the terminal. SCRs are mainly used where high currents and voltage are involved and are often used to control alternating currents, where the change of sign of the current causes the device to automatically switch off.

For example a dimmer switch of light can be implemented using a SCR. Where the turn on point is controlled to occur at a particular point on the sine curve of the AC supply. The SCR stays on for the remainder of that cycle. The drawback of using SCRs is that like diodes they only conduct in one direction.


7. ICs: - (Integrated circuits)

IC’s, often called “chips”, come in several shapes and size. Most common are 8, 14, or 16 pin dual in line (dil) chips. IC’s can be soldered directly into printed circuit board. When soldering, ensure that the IC (or the socket) is the correct way round and that no pins have been bent underneath the body.

When fitting new IC’s sit is often necessary to bend the pins in slightly, in order to fit it into the board (or socket).

Some IC’s are damaged by the static electricity which most people carry on their bodies. They should be stored in conductive foam or wrapped in tin foil. When handling them, discharge yourself periodically by touching some metal work which is earthed, such as a radiator.

Solder two diagonally opposite pins (say pin 1 and pin 5 in the diagram below) and check that the IC is flat on the board before soldering the rest. If it is not flat then reflow the solder on the two pins pushing the IC flat. When satisfied, solder the remaining pins.

Take when removing faulty IC’s from PCB’s.  You may damage a 100 pound board when carelessly removing a 20p IC.


Figure:-1.5, IC 555





8 Photo diode

Figure 1.6, Photodiode: A light-sensitive diode

Photodiode is an electric component and a type of photo detector. It is a p-n junction designed to be responsive to optical input. Photodiodes can be used in either zero bias or reverse bias.  In zero bias, light falling on the diode causes a voltage to develop across the device, leading to a current in the forward bias direction. This is called the photovoltaic effect, and is the basis for solar cells-in fact a solar cell is just a large number of big, cheap photodiode.

9. Photo Transistor: - Phototransistors are junction transistors that are sensitive to incident radiation.                              100px-PhototransistorSymbol

                    Figure 1.7, Phototransistor: A Light-sensitive transistor

10. LED: - LED                                      



                                                 Figure 1.8, Light Emitting Diode  

A transducer which converts electrical energy to light. The Light Emitting Diode (LED) is commonly used as an indicator. It can show when the power is on, act as a warning indicator. LED’s convert an electrical current directly into light. The light emitted by an LED is directly proportional to current through the LED. This means LED’s are ideal for transmission of information.





11. LDR:-


                                                                           Figure 1.9, LDR

Some resistors change in value when exposed to light. They are called Light Dependent Resistors.

12. Potentiometer:-


                                                       Figure 1.10, Potentiometer

Potentiometer: A Variable resistor often connected as a voltage divider to create variable voltages when used as a rotational position sensor.


We have identified, studied and tested the various electronic components.

Click Here to Download Doc File

comments (0)