This document discusses different types of variable capacitors and inductors. It describes that variable capacitors have capacitance that can be varied by rotating a shaft, and includes ganged and trimmer capacitors. Inductors are coils that produce a magnetic field opposing changes in current through the coil. Types of inductors include air core, iron core, and ferrite core inductors. The document also covers voltage ratings of capacitors, tolerance of capacitors, and mutual inductance between two coils.

1. B.SC I SEM I
ELECTRONICS
- PROF. D.B.BOBADE

2. VARIABLE CAPACITOR
• These are the capacitors whose capacitance can be varied by
rotating a shaft called as variable capacitor.
• TYPES OF VARIABLE CAPACITOR:
1. Ganged capacitor
As shown it consists of a set of conducting plates mounted on shaft.
Due to the movement of shaft, the value of capacitance can be
changed. The other set of plates is kept fixed.

3. 2. Trimmer or padder capacitor:
As shown, it consists of two small
flexible metal plates separated by solid
dielectric i.e. mica or ceramic slab. The
spacing between the plates can be
changed by means of adjusting screw
and hence capacitance can be adjusted.
Capacitance of trimmer can be changed
from 5 pF to 30 pF.
These variable capacitors are
used in radio receiver for tuning
different radio stations.

4. VOLTAGE RATING OF CAPACITOR
• It is given by maximum potential difference applied across its plates
without dielectric.
• Such ratings are given for temperature upto 60 degree Celsius.
• Higher temperature results in lower voltage rating. E.g. DC voltage
rating of mica, ceramic, plastic capacitors are 200 – 500 V.
• For electrolytic capacitor, 25, 150 – 450 V.
• The AC voltage rating for capacitor is less because of internal heat
produced by charging and discharging of capacitor.

5. TOLERANCE OF CAPACACITOR
• It is maximum and minimum value of capacitance in percentage.
• E.g. ceramic capacitor ± 20%, mica capacitor ± 1% or 2%, paper
capacitor ± 10%

6. INDUCTOR
• It is nothing but a coil wound on a core or former of some suitable
material.
• When an electric current passes through a coil, a magnetic field is
produced which opposes any change in current thereby maintains a
steady current, this is called as inductance and unit is Henry.
• Suppose, current through an inductor is changed at the rate of dI/dt,
then it is found that e = L.dI/dt or L = e/dI/dt.
• If dI/dt = 1 A/s and e =1V, then L = 1H.
• Hence, a coil has an inductance 1H if an emf of 1V is induced in it
when current through it changes at the rate of 1 A/s.

7. • The main function of inductor is to block AC and allow to pass DC.
• The amount of opposition to flow of AC is called as inductive
reactance and unit is ohm and given by XL = 2𝜋FL.
• TYPES OF INDUCTOR:
1. Air core inductor:
It consists of number of turns of wire wound on a former made of
ordinary cardboard. As there is air inside the coil, it has least
inductance for a given number of turns and core length.
2. Iron core inductor:
It consists of a coil of wire wound on a solid iron core. It has more
inductance due to iron inside.

8. 3. Ferrite core inductor:
It consists of a coil of wire wound on a solid core of ferrite. It has a
high value of inductance. The symbol of air, iron and ferrite core
inductor is as shown.

9. MUTUAL INDUCTANCE
• When two coils are placed so close to each other, then due to
expanding and collapsing magnetic flux of one coil, an induced emf
is produced in other coil, then these two coils are said to have
mutual inductance and given by m = e/di/dt.
• Two coils are said to be magnetically coupled if full or part of flux
produced by one coil linked with other.
• Closer the two coils, tight will be coupling.
• This coupling effect is measured in coefficient of coupling and given
by, 𝐾 = 𝑀/√𝐿1. 𝐿2 where L1 indicates inductance of one coil, L2
inductance of second coil, M indicates mutual inductance.