Page 22 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

The colour coding of capacitors and resistors are same. Where as, in the case of fixed capacitors, the colour
coded unit shall be in Picofarads.
For letter coding, incase of capacitor, the letter ‘p’, ‘n’, ‘m’ shall be used as multipliers. Where p = 10-12, n= 10-9
and m = 10-6 farads, and letter code for tolerance on capacitor is the same as in resistor.
Inductor: The ability of the conductor to induce voltage in itself, when the current changes in it is called as self
inductance (or) simply inductance. A coil introduced in a circuit to have inductance is called as inductor. Different
type of inductors are shown in Fig 7. The unit of inductance is “Henry”. Commercially a coil may have inductance
in Millihenry (10-3H), or in Microhenry (10-6H).

Fig 7

While specifying the inductance the following factors to be considered
• nominal value of inductance in Henry / Millihenry / Microhenry.

• tolerance in percentage (±5/10/20%)
• type of winding like single layer, double layer, multilayer and pie (p) etc.
• type of core like air core, iron core, ferrite core
• type of application like audio frequency (AF), Radio frequency (RF) coupling coil, filter coil etc.,

In an electronic circuit some time, it is also required to vary the inductance.
The inductance of a coil can be varied by:-
• providing tapped inductive coil, as in Fig 8 or
• adjusting the core of a coil as in Fig 9.
However, all inductor coils have inherent resistance due to the resistance of the winding wire in the coil. Further
the maximum current that can be safely carried by an inductor depends upon the size of the winding wire used.
Active components
In electronic circuit, the components, other than passive are known as active components. Namely, transistors,
diodes, SCRs Vacuum tubes etc.,
Active components : In electronic circuits, components other than resistors, capacitors and inductors are also
used. Namely, transistors, diodes, vacuum tubes, SCRs, diacs, zener-diode (Fig 10) etc. The application of
electrical circuit laws (Ohm’s law etc.) in the circuit containing the above components will not give correct results.
i.e. these components do not obey. Ohm’s law, Kirchoff’s law etc. These components are called active components.

The different active components and the method of representing them by symbols in the circuit diagram are given
below (Fig 10)
The different types of diodes (Fig 11) used for specific purposes are represented by the symbols given.

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CITS : Power - Electrician & Wireman - Lesson 60-69