Download Chapter 16 Class 10th

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INTRODUCTORY ELECTRONICS
Q.1 What is electronics? Describe its branches.
(Ans) Electronics
The branch of physics that deals with the devolpement of electron
emmiting devices and their utilization.
There are two main branches of electronics.
i. Analogue electronics
ii. Digital electronics
Analogue electronics
The branch of electronics that consists of electronic circuits which works
on analogue quantities is known as analogue electronics.
Analogue quantities
Those quantities whose value vary continuously or remain constant are
known as analogue quantities.
For example
Temperature of air changes continuosely during day and night.
Digital electronics
The branch of electronics that consists of electronic circuits which works
on digital data is known as digital electronics.
Digital data
A digital data processed on two digits ie zero (0) and one (1). This data
can be easily processed, because the whole data is provided in binary
system.
Uses
Digital electronics technology is used in computers, telephone, radar,
medical equipments, etc.
Q.2 What is meant by thermionic emission?
(Ans) Thermionic emission
The emission of electrons from a metallic surface due to the gain of heat
energy is called thermionic emission.
Explanation
Metals have free electrons that form a sea over the surface of their
material. When we give heat to a metallic substance, these electrons gain
energy and become excited. Some of the electrons may gain enough
energy to escape from the surface of the metal.
Q.3 Write a note on electron gun.
(Ans) Electron gun
The device use to investigate the properties of the electron beams is
known as electron gun.
Costruction
It consists of a glass tube at a very low pressure. The electrons are
produced by thermionic emission from a tungsten filament heated by a 6V
supply. A high positive potential (several thousands volts) is connected to
a cylindrical anode (+). The electrons will be accelerated to high speed
and they shoot straight through the hole of the anode in a fine beam of
electrons. This electron beam is also called as cathode rays (-). The path
of these free electrons can be affected by electric and magnetic field.
Deflection by electric field
An electric field can be set up by appling a potential difference across two
parallel metal plates placed horizontally some distance apart.
When an electron beam passes between the two plates, it can be
observed that the electrons are deflected towards the positive plate. The
reason being that electrons are attracted by the positive plate and repelled
by the negative plate.
Delection by magnetic field
A magnetic field is applied at right angle to the beam of electrons by
placing two poles of the magnet. It can be observed that the electron
beam is deflected by the magnetic field.
We concluded that cathode rays are actually negatively charged electrons.
Q.4 Explain construction, working, principle and uses of C.R.O?
(Ans) Cathode ray oscilloscope
An electronic device that becomes a part of everyday life.
Construction
It consists of the following components:
i. The electron gun
ii. The deflecting plates
iii. A fluorescent screen
(i)
The electron gun
It consists of a grid, which is connected to a negative potential. The more
negative the potential, more electrons will be repelled from the grid and
fewer electrons will reach the anode and the screen. The number of
electrons reaching the screen determines the brightness of the light. The
other feature in the electron gun is the use of the anode. Anode
accelerates the electrons towards the screen.
(ii)
The deflecting system
Two pairs of plates are fitted in cathode ray oscilloscope. Voltage can be
applied to these plates to deflect the electron beam. The Y-plate deflects
the electron beam vertically while the X-plate deflect electron beam in
horizontal direction.
(iii) The fluorescent screen
The screen is coated with a fluorescent salt, for example, zinc sulphide.
When the electrons hit the screen, it will cause the salt to produce a flash
of light and hence a bright spot on the screen.
Principle
A cathode ray oscilloscope works on the principle, when the electron
beam falls on the fluorescent screen forms a wave on the screen. As a
result, we can know understand the strength of the wave from the
brightness of the wave.
Uses
A cathode ray oscilloscope is used in the screen of televisions and
computer monitors. It is also used to study the waveform of a repetitive
electronic signal.
Q.5
What are electronic logic gates? Describe different types of logic
gates.
(Ans) electronic logic gates
To keep the precious things, cash or important documents in safe custody
safes are used. The doors of such safes are opened and closed by a set
of switches to be used in proper order. This synthetic order system is
called electronic logic gates. If the buttons of the safe are pressed in
proper order, then the safe will opened. Otherwise, the door will start
alarming.
Types of logic gates
The different types of logic gates are as under.
i)
NOT-GATE
The NOT gate is also known as inverter, because it changes “ON” to
“OFF” and “OFF” to “ON”, that is if input is zero “0” then the output will be
one “1”. As shown in the truth table below.
Truth table
Input
Output
A
A
0
1
1
0
Symbol of “NOT” gate
A
ii)
OR-GATE
In case of “OR” gate the output will be “ON” if both the input or any one
input is “ON” and bulb will be on. The output will be “OFF” if both inputs
are “OFF” as shown in truth table below.
Truth table
Input
Input
Output
A
B
A+B
0
0
1
1
0
1
0
1
0
1
1
1
Symbol of “OR” gate
A+B
iii)
AND-GATE
in case of “AND” gate the output will be “ON” if both the input are “ON”
and the bulb will on and output will be “OFF” if any one of them is “OFF”
as shown in truth table below.
Truth table
Input
Input
Output
A
B
A.B
0
0
1
1
0
1
0
1
0
0
0
1
Symbol of “AND” gate
A
AB
B
iv)
NAND-GATE
In case of “NAND” gate the output of “AND” gate is inverted, which can be
explained in truth table below.
Truth table
Input
Input
Output
A
B
A.B
0
0
1
0
1
0
1
1
1
1
1
0
Symbol of “NAND” gate
A
AB
B
v)
NOR-GATE
In case of “NOR” gate the output of “OR” gate is inverted, which can be
explained in truth table below.
Truth table
Input
Input
Output
A
B
A B
0
0
0
1
1
0
1
1
0
1
0
0
Symbol of “NOR” gate
A
B
A B
USES OF LOGIC GATES
 Wireless door and window alarm
To prevent that your child do not walked outside the front door without
telling you, a special type wirless door alarms can prevent such a risk and
keep your child safely inside. When the door is opened the alarm emits a
continous 120 db sound (until the door is shut) to tell you that your child is
at risk of leaving.
 Other uses of logic gates
Logic gates are used in computers, mobiles, calculators, digital watches,
etc.
Short questions
1.
What are the logic values of P, Q and R in the following logic circuit?
See fig in book.
A. The value of P is 1 (NOT-GATE), the value of Q is 1 (AND-GATE), while
the value of R is 1 (OR-GATE).
2.
Identify the logic gates below and write out their respective truth
table?
See fig in book.
See Q.5
Name five digital devices that are commonly used in everyday life.
Name of five digital devices that are commonly used in daily life is;
1. Computer 2. Telephone 3. Fax machine 4. Calculator 5. Digital watch
A.
3.
A.
4.
A.
What do you mean by analogue?
See Q.1