Chapter 16 Basic Electronics Ā (Long Questions)
Ā (a) a uniform electric fieldĀ (b) a uniform magnetic field. What do these results indicate about the charge on electron?
16.2. Explain the working of different parts of oscilloscope.
16.3. Name some uses of oscilloscope.
16.4. Considering an oscilloscope explain:
(i) How the filament is heated?
(ii) Why the filament is heated?
(iii) Why the anode potential is kept positive with respect to the cathode potential?
(iv) Why a large potential is applied between anode and cathode?
(v) Why the tube is evacuated?
16.5. What is electron gun? Describe the process of thermionic emission.
16.6. What do you understand by digital and analogue quantities?
16.7. Differentiate between analogue electronics and digital electronics. Write down names of five analogue and five digital devices that are commonly used in everyday life.
16.8. State and explain for each case whether the information given by the following devices is in analogue or a digital form.
a. a moving-coil voltmeter measuring the e.m.f of a cell.
b. a microphone generating an electric current.
c. a central heating thermostat controlling the water pump.
d. automatic traffic lights controlling the flow of traffic.
16.9. Write down some benefits of using digital electronics over analogue electronics.
16.10. What are the three universal Logic Gates? Give their symbols and truth tables.
CONCEPTUAL QUESTIONS
16.1. Name two factors which can enhance thermionic emission.
16.2. Give three reasons to support the evidence that cathode rays are negatively charged electrons.
16.3. When electrons pass through two parallel plates having opposite charges, they are deflected towards the positively charged plate. What important characteristic of the electron can be inferred from this?
16.4. When a moving electron enters the magnetic field, it is deflected from its straight path. Name two factors which can enhance electron deflection.
16.5. How can you compare the logic operation X=A.B with usual operation of multiplication?
16.6. NAND gate is the reciprocal of AND gate. Discuss
16.7. Show that the circuit given below acts as OR gate.
16.8. Show that the circuit given below acts as AND gate.
16.1. Describe, using one simple diagram in each case, what happens when a narrow beam of electrons is passed through
Ā (a) a uniform electric fieldĀ (b) a uniform magnetic field. What do these results indicate about the charge on electron?
Ans. (a) A uniform Electric Field:
When an electron beam is passed through a uniform electric field it deflects and accelerates the electron beam as shown in figure.
(b) A uniform Magnetic Field:
When an electron beam is passed through a uniform magnetic field it only deflects the electron beam. The two above results show that electrons carry negative charge.
16.2. Explain the working of different parts of oscilloscope.
Ans. TheĀ CRO stands for a cathode ray oscilloscope. It is typically divided into four sections which are display, vertical controllers, horizontal controllers, and Triggers. Most of the oscilloscopes are used the probes and they are used for the input of any instrument. We can analyze the waveform by plotting amplitude along with the x-axis and y-axis. The applications of CROās mainly involve in the radio, TV receivers, also in laboratory work involving research and design. In modern electronics, the CRO plays anĀ important role in the electronic circuits.
16.3. Name some uses of oscilloscope.
Ans. Uses: Cathode ray oscilloscope is a versatile electrical instrument which is in fact a high speed graph plotting device.
1. Voltage Measurement: Enter the unknown voltage at “Y -input” and the “VOLT/DIV” knob at the oscilloscope can be tuned to be used as voltmeter.
2. Time Measurement: By adjusting the “TIME/DIV” knob the oscilloscope can be used to measure the time.
3. To show the x-t signal: Oscilloscope can display the time signal (voltage-time or current-time)Ā output whether it can be shown in beat high frequency wave.
4. To show the x-y graph: The relation between two variables can be displayed by entering a horizontal signal and vertical signal.
16.4. Considering an oscilloscope explain:
(i) How the filament is heated?
(ii) Why the filament is heated?
(iii) Why the anode potential is kept positive with respect to the cathode potential?
(iv) Why a large potential is applied between anode and cathode?
(v) Why the tube is evacuated?
Ans. i. Filament is heated by a battery usually of 6 Volts.
ii. Filament is heated to get the electrons by thermionic emission.
iii. The anode potential is positive with respect to the cathode because electrons being negatively’ charged particles are accelerated towards the anode (positive potential).
iv. The degree of deflection and acceleration produced in electrons is proportional to the strength of the electric field. So high potential will accelerate the electrons to high speed and they shoot straight through the hole of the anode in a fine beam of electrons.
v. The tube is evacuated because electrons could not collide with other gas to give rise other electrons and ions.
16.5. What is electron gun? Describe the process of thermionic emission.
Ans. Electron Gun: Electron gun is an important mean to provide continuous beam of electrons. It consists of a evacuated glass tube at a very low pressure. The electrons are produced by thermionic emission from a tungsten filament heated by a battery, usually 6 V supply.
A high positive potential (several thousands) is applied to cylindrical anode (+). The electrons will be accelerated to a high speed and they shoot straight through the hole of the anode in a fine beam of electrons.
16.6. What do you understand by digital and analogue quantities?
Ans. (1) Analogue Quantities:
The analogue quantities are those whose values vary continuously. For example the variation of temperature with time during a day is shown by the help of a graph shown below.
This shows that temperature variation with time is continuous. So we can say that temperature is an analogue quantity with respect to time. Similarly, pressure, distance covered by a moving car etc. are all analogue physical quantities.
Digital Quantities:
The Part of electronics which processes the data provided in the form of digits or numbers is known as “digital electronics”.
Digital electronics uses only two numbers 1 (high) and 0 (low), the whole data is provided in binary system due to which processing has become very easy.
16.7. Differentiate between analogue electronics and digital electronics. Write down names of five analogue and five digital devices that are commonly used in everyday life.
Ans. Analogue Electronics: The section of electronics, which is concerned with circuits processing analogue quantitiesĀ like current, voltage etc. is called analogue electronics.
Digital Electronics: Digital electronics use the digital signal In a sequence of voltage pulses represented in binary digits “0” and “1”.
Computer operates by counting the digits,
Five Analogue Devices:
(l)Refrigerators Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā (2) Electric fans Ā Ā Ā Ā Ā Ā Ā Ā (3) Electric iron
(4) Electric lamps Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā (5)Radio receiver.
Five Digital Devices:
(1) Computer Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā (2) T.V. Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā (3) Digital camera
(4) Mobile (Cell) phone Ā Ā Ā Ā Ā Ā Ā Ā Ā Ā (5)Security system
16.8. State and explain for each case whether the information given by the following devices is in analogue or a digital form.
a. a moving-coil voltmeter measuring the e.m.f of a cell.
b. a microphone generating an electric current.
c. a central heating thermostat controlling the water pump.
d. automatic traffic lights controlling the flow of traffic.
Ans. a. It is analogue device which measure the value of e.m.f of a cell. The deflection of the moving-coil is continuous variation with time. It is analogue signal.
b. A public address system shown in figure below is an example of analogue electronic system.
The microphone converts sound energy into continuously varying voltage/current. It is called analogue voltage/current signal. This signal is applied to an amplifier; which is also analogue electronic circuit, which amplifies the signal without changing its shape, which operates the loud speaker.
c. Thermostat controlling the flow of traffic.
The thermostat ‘depends upon the atmospheric temperature which vanes continuously with time. It is an analogue signal. So the thermostat controlling the flow of traffic is an analogue device.
d. Automatic traffic lights controlling the flow of traffic.
It is an digital system which is being operated between two values” 1″ high (Present) and 10w”O” (Not present).
16.9. Write down some benefits of using digital electronics over analogue electronics.
Ans. Digital electronics use the digital signal in a sequence of voltage pulses represented in binary digits “O” and “I”. Computer operates by counting the digits. The process with numbers becomes fast, reliable and less error as compared to analogue signal.
Digital electronics is being used in every modem electronic device like modern telephone system, radar system, naval and other military controlling systems, modern cameras,’ control system of operation of industrial machines, medical equipf!1ent etc.
16.10. What are the three universal Logic Gates? Give their symbols and truth tables.
Ans.Ā AND,Ā ORĀ andĀ NOTĀ are the three universal Logic Gates.
The AND Gate
In Boolean Algebra theĀ ANDĀ function is the equivalent of multiplication and so its output state represents the product of its inputs. TheĀ ANDĀ function is represented in Boolean Algebra by a single ādotā (.) so for a two inputĀ ANDĀ gate the Boolean equation is given as:Ā QĀ =Ā A.B, that isĀ QĀ equals bothĀ A AND B.
The 2-input Logic AND Gate
The OR Gate
In Boolean Algebra theĀ ORĀ function is the equivalent of addition so its output state represents the addition of its inputs. In Boolean Algebra theĀ ORĀ function is represented by a āplusā sign (+) so for a two inputĀ ORĀ gate the Boolean equation is given as:Ā QĀ =Ā A+B, that isĀ QĀ equals eitherĀ A OR B.
The 2-input Logic OR Gate
The NOT Gate
TheĀ NOTĀ gate, which is also known as an āinverterā is given a symbol whose shape is that of a triangle pointing to the right with a circle at its end. This circle is known as an āinversion bubbleā.
TheĀ NOTĀ function is not a decision making logic gate like theĀ AND, orĀ ORĀ gates, but instead is used to invert or complement a digital signal. In other words, its output state will always be the opposite of its input state.
TheĀ NOTĀ gate symbol has a single input and a single output as shown.
The Logic NOT Gate
CONCEPTUAL QUESTIONS
16.1. Name two factors which can enhance thermionic emission.
Ans. Thermionic Emission depends upon:
- The substance used as filament because different materials have different number of free available electrons.
- The value of the battery used to make it heated.
16.2. Give three reasons to support the evidence that cathode rays are negatively charged electrons.
Ans. 1. The cathode rays are deflected and accelerated towards’ positively charged plate .
2. The deflection of cathode rays is the presence of magnetic field shows. that these are negatively charged particles.
3. Grid in the oscilloscope is negatively charged and the electrons are repelled by the. grid It shows that cathode rays (electron beam) is negatively charged particles.
16.3. When electrons pass through two parallel plates having opposite charges, they are deflected towards the positively charged plate. What important characteristic of the electron can be inferred from this?
Ans. If electrons will deflect towards the positive charged plate it means electrons are negatively charged particles.
16.4. When a moving electron enters the magnetic field, it is deflected from its straight path. Name two factors which can enhance electron deflection.
Ans. Fast moving electrons pass through magnetic field, they are deflected from their straight path shows that these are charged particles. The deflection can be enhanced by increasing the velocity and magnetic field strength.
16.5. How can you compare the logic operation X=A.B with usual operation of multiplication?
Ans. There is logic operation which is give by the equation (X = A.B). It is called AND gate.
This particular gate holds the usual operation of multiplication.
The truth table of this gate is given below.
16.6. NAND gate is the reciprocal of AND gate. Discuss
Ans. NAND gate is not reciprocal of AND gate. We can say that NAND gate is inversion of AND gate. If X is output of NAND gate then
mathematically we can write asĀ Ā 
16.7. Show that the circuit given below acts as OR gate.
Ans. Yes it acts the OR gate. If X is output of the circuit shown above then mathematically We can write as
Its truth table is given. below.
| A | B |  |
 |
| 0 | 0 | 1 | 0 |
| 1 | 0 | 0 | 1 |
| 0 | 1 | 0 | 1 |
| 1 | 1 | 0 | 1 |
16.8. Show that the circuit given below acts as AND gate.
Ans. Yes, it acts as AND gate. If X is output of the circuit shown above then
mathematically we can write asĀ
Its truth table is given below.
| A |  |
B |  |
|
| 0 | 1 | 0 | 1 | 1 |
| 1 | 0 | 0 | 1 | 0 |
| 0 | 1 | 1 | 0 | 0 |
| 1 | 0 | 1 | 0 | 0 |