Electronics

By Dr Vipan Goyal
• Electronics : It is a branch of physics and technology
concerned with the behaviour and movement of electrons.
• Diode valve : Designed by J.A.Fleming.
• It consists of two electrodes placed inside an evacuated
glass envelope.
• One electrode is called cathode which is made up of
tungsten on which there is a thin layer of barium oxide.
• When heated, cathode emits electrons. These electrons
flow towards the other electrode called anode or plate,
which is at positive potential.
• As a result an electric current is established in the circuit.
• The electrons emitted from cathode are collected in the evaluated space around it.
• This collection of electrons is called space charge which is obviously negative.
• Diode valve acts as a rectifier.
• Rectifier is a device which converts alternating voltage (current) into direct voltage
(current).
• Triode valve : Designed by Lee de Forest,
triode valve is a modified form of usual diode.
• It consists of a usual anode-cathode pair and
one more electrode called control grid.
• Triode valve can be used as amplifier,
oscillator, transmitter and detector.
 Electric Current
• An electric current is a flow of microscopic particles called electrons
flowing through wires and components.
• The Current Always Flows In Positive To Negative Terminal.
• For current to flow you must have a complete circuit contains battery, key,
wire and bulb etc.
• A Power source is needed to create a Potential Difference (form greater Pd
to lower Pd). When these conditions are met free electrons move about
inside the metal. Charges will continue to move as long as the potential
difference (voltage) is maintained. It will not flow if the potential
difference of the conductor is same.
 Measuring Current
• Specifically, electric current is the rate that electric charge passes a point,
so, Current = Charge/Time or I = q/t
• If a net charge Q, flows across any cross-section of a conductor in time t,
then the current I, through the cross-section is-
I = Q/t
• Unit of Electric Current: The SI unit of electric current is Ampere. Ampere
is defined as one coulomb of charge moving past a point in one second. If
there are 6.241 x 1018 electrons flowing through our frame in one second
then the electrical current flowing through it is ‘One Ampere.’
 Question
• Calculate the average current in a wire through which a charge of
15C passes in 10s ?

• Solution
 I = 15C/10s = 1.5 C/s (Ampere)
 Charge pump is needed for maintaining the charge.
 Properties of Electric Current
• Electric current is an important quantity in electronic circuits. We have
adapted electricity in our lives so much that it becomes impossible to
imagine life without it. Therefore, it is important to know the properties of
electric current.
• We know that electric current is the result of the flow of electrons.
• The work done in moving the electron stream is known as electrical
energy.
• The electrical energy can be converted into other forms of energy such as
heat energy, light energy, etc.
• For example, in an iron box, electric energy is converted to heat energy.
Likewise, the electric energy in a bulb is converted into light energy.
• There are two types of electric current known as alternating current (AC)
and direct current (DC).
• The direct current can flow only in one direction, whereas the alternating
direction flows in two directions.
• Direct current is seldom used as a primary energy source in industries. It
mostly used in low voltage applications such as charging batteries, aircraft
applications, etc.
• Alternating current is used to operate appliances for both household and
industrial and commercial use.
• The electric current is measured in ampere. One ampere of current
represents one coulomb of electric charge moving past a specific point in
one second.
1 ampere = 1 coulomb / 1 second
• The conventional direction of an electric current is the direction in which a
positive charge would move.
• Henceforth, the current flowing in the external circuit is directed away
from the positive terminal and toward the negative terminal of the
battery.
 Heating Effect of Electric Current
• When our clothes are crumpled, we use the iron box to make our clothes
crisp and neat. Well, you might wonder how does the iron box get hot?
• The heating effect of electric current is the answer to this. There are many
such devices that work on the heating effect.
• When an electric current flows through a conductor, heat is generated in
the conductor.
• The heating effect depends on the following factor:
 The time ‘t‘ for which the current flows : The longer the current flows
in a conductor more heat is generated.
 Heating Effect of Electric Current
 The electrical resistance of the conductor : Higher the
resistance, higher the heat produced.
 The amount of current : The larger the amount of current
higher the heat produced.
 The heating effect is given by the following equation

H=I2RT
 Magnetic Effect
• When current flows through a wire, a magnetic field is developed around it.
• If a current-carrying wire is brought near to a bar of iron, it gets magnetised and
when the current flow is stopped, the iron bar loses its magnetism.
• Electromagnets produced in this way have lot of applications.
• They are used for lifting and transporting steel plates, scrap iron etc.
• They are also used in electric bells, telephone receivers, etc.
• Magnetic field is a quantity that has both direction and magnitude. The direction
of the magnetic field is taken to be the direction in which a north pole of the
compass needle moves inside it.
 Magnetic Effect
• Therefore it is taken by convention that the
field lines emerge from North Pole and
merge at the South Pole.
• Inside the magnet, the direction of field
lines is from its south pole to its north pole.
Thus the magnetic field lines are closed
curves.
• The relative strength of the magnetic field
is shown by the degree of closeness of the
field lines.
• The field is stronger, that is, the force
acting on the pole of another magnet
placed is greater where the field lines are
crowded.
 Magnetic Effect
• No two field-lines are found to cross each other.
• If they did, it would mean that at the point of intersection, the compass
needle would point towards two directions, which is not possible.
• An electric current through a metallic conductor produces a magnetic field
around it.
 Chemical Effect, Electrolysis
• When electric current passes through a
solution, it results in decomposition of the
solution into negative and positive ions.
• Positive ions are collected at the negative
electrode i.e. cathode and negative ions
are collected at the positive electrode i.e.
anode. This process is called electrolysis.
This process is widely used in
electroplating.
• For example, chromium plating is done on
many objects such as car parts, bath taps,
kitchen gas burners, bicycle handlebars,
wheel rims and many others.
 Chemical Effect, Electrolysis
• Tin cans, used for storing food, are made by electroplating tin onto iron.
Tin is less reactive than iron. Thus, food does not come into contact with
iron and is protected from getting spoilt.
• Iron is used in bridges and automobiles to provide strength. However, iron
tends to corrode and rust. So, a coating of zinc is deposited on iron to
protect it from corrosion and formation of rust.
 LEDs
• LEDs (Light Emitting Diodes) are available in
many colours such as red, green, yellow, blue,
white and are increasingly being used for
many applications, for example in traffic signal
lights.
• LEDs are increasingly being used for lighting.
• A cluster of white LEDs grouped together
forms a LED light source.
• LED light sources consume less electricity and
have longer lifetime than light bulbs and
fluorescent tubes.
• But LED light sources are expensive, so CFLs
are currently the best choice.
 CFLs (Compact Fluorescent Lamp)
• However, CFLs (compact fluorescent
lamp) contain mercury which is toxic.
• Therefore, used or broken CFLs need to be
disposed off safely.
• Once the technological advances reduce
the cost of LEDs, they will become the
preferred lighting source.
 Electric Motor
• In an electric motor, electric energy is converted into
mechanical energy.
• Electric motors are used in electric fans, washing
machines etc.
• In loudspeakers, energy is transferred from electric
current into mechanical energy of vibration.
• A device that reverses the direction of flow of
current through a circuit is called a commutator.
• In electric motors, the split ring acts as a
commutator. The reversal of current also reverses
the direction of force.
 Electric Motor
• The commercial motors use:
 an electromagnet in place of permanent
magnet;
 large number of turns of the conducting
wire in the current carrying coil; and
 a soft iron core on which the coil is
wound.
• The soft iron core, on which the coil is
wound, plus the coils, is called an armature.
This enhances the power of the motor.
 Galvanometer
• A galvanometer is an instrument
that can detect the presence of a
current in a circuit.
• The pointer remains at zero (the
centre of the scale) for zero
current flowing through it.
• It can deflect either to the left or
to the right of the zero mark
depending on the direction of
current.
 Electric Generator (Dynamo)
• In a generator, the armature is rotated
in the magnetic field and an emf is
generated in it due to electromagnetic
induction.
• Thus a generator converts mechanical
energy into electrical energy.
• With a minor change in construction, a
generator can produce alternating emf
or direct emf.
• The corresponding currents produced
are called alternating Current (ac) and
direct Current (dc).
 Inverter
• An inverter converts DC to AC. The
inverters for home and office purpose
are designed to convert DC from a
battery to AC, and also to charge the
battery.
• If there is a power failure, the inverter
automatically switches on the AC,
converted from the battery’s DC.
• After the mains supply is restored, the
inverter automatically switches to a
mode where it starts charging the
battery.
 Electric Potential And Potential Difference
• The electric potential difference between two points in an electric circuit
carrying some current is the work done to move a unit charge from one
point to the other;
• Potential difference (V) between two points = Work done (W)/Charge
(Q)
V = W/Q
• The SI unit of electric potential difference is volt (V), named after
Alessandro Volta (1745–1827), an Italian physicist.
 Electric Potential And Potential Difference
• One volt is the potential difference between two points in a current
carrying conductor when 1 joule of work is done to move a charge of 1
coulomb from one point to the other.
• The potential difference is measured by means of an instrument called
the voltmeter.
• The voltmeter is always connected in parallel across the points between
which the potential difference is to be measured.
 Type of Materials
• Conductors are those type of materials which have number of free
electrons to conduct the electricity.
• The metals are good conductors of electricity.
• Metals like silver, iron, copper and earth acts like a conductor.
• Silver is the best conductor.
• Insulators are that type of materials which do not have the free electrons
in its volume and hence, it does not conduct the electricity at all.
• Metals like wood, paper, mica, glass, ebonite are insulators.
 Type of Materials
• Semiconductor is that type of
materials which do not have
free electrons at the normal
temperature, but has the free
electrons at the increased
temperature and hence,
behaves like a conductor.
• The materials such as silicon,
germanium etc., are the
semiconductor.
• Intrinsic Semiconductor : A semi conductor is an extremely pure form is known as intrinsic
semi conductor.
• Extrinsic Semiconductor : If a measured and small amount of chemical impurity is added to
intrinsic semi conductor, it is called extrinsic semiconductor or doped semi conductor. As a
result of doping, there is a large increase in its conductivity.
• Extrinsic semi conductors are of two types :
• A) N type semi conductor : An extrinsic semi conductor in which electrons are majority
charge carrier is called N type semi conductor. Such a semi conductor is made by doping a
pure semi conductor with pentavalent impurity like Arsenic, Antimony and Phosphorus.
• B) P type semi conductor : An extrinsic semi conductor in which holes are majority charge
carrier is called P type semi conductor. Such a semi conductor is made by doping a pure semi
conductor with trivalent impurity like Gallium, Indium, Boron and Aluminium.
 Terms associated
• Doping : Adding of chemical impurity to a pure semi
conductor is called doping. The amount and type of impurity
is closely controlled.
• Donor : Pentavalent impurity are called donor.
• Acceptor : Trivalent impurity are called acceptor.
• The electrical conductivity of a semi conductor increases with
the increase in the temperature.
Thank You