Electronics questions and answers, transistor, transducer,quiz

Multiple choice questions

1. Substances which allow electric current to pass through them are called

a) Conductors b) insulation c) semi conductors d) none of the above

2. Electric charge carriers in a P-type semi conductor are

a) Electrons b) holes c) protons d) neutrons

3. Electric charge carries in an n-type semi conductors are

a) Electrons b) holes c) Protons d) neutrons

4. with the rise in temperature, the resistance of a semi conductor

a) increases b) remains unchanged c) decreases d) first decreases and then increases

5. When the temperature of a semi conductor is increased, its electrical conductivity

a) Increases b) remains unchanged c) decreases d) first decreases then increases

6. The binding in semiconductor is

a) Covalent b) ionic c) mutual d) metallic

7. The element that can be used as an acceptor impurity to dope Silicon is

a) Antimony b) arsenic c) boron d) phosphorous

8. The valency of donor impurity used for doping used for doping germanium crystals is

a) 2 b) 3 c) 4 d) 5

9. If Silicon has to be doped with a donor impurity, the foreign atom should be

a) Tetravalent b) trivalent c) mono valent d) penta valent

10. p-n junction diode works as an insulator if connected

a) To ac source b) in forward bias c) in reverse bias d) either to AC source or reverse bias

11. The resistance of a p-n junction in forward bias is

a) Zero b) low c) high d) infinite

12. A device that converts one type of energy into another type of energy is called

a) A transmitter b) a receiver c) an amplifier d) a transducer

13. The device that converts electrical energy into corresponding sound signal is

a) A transmitter b) a receiver c) a microphone d) a loud speaker

Fill in the blanks:

1. The conductivity of a semi conductor is increased by adding ____________to a pure semi conductor2. In an n-type semi conductor holes are ___________ carriers

3. In a p-type semi conductor __________________ are majority charge carriers

4. n-type semi conductor is prepared by adding ____________ impurities to a pure semi conductor.

5. The valency of germanium is _______________

6. If arsenic is doped to silicon, then its conductivity _____________

7. Least doped region in a transistor is ______________

8. The scientist who transmitted a message across the Atlantic in 1901 is _______________

9. The device that converts sound energy into corresponding electrical signal is ______________

10. In TV, the amplified video signal is used to ______________ modulate an RF carrier

11. When boron is added to germanium crystals ____________ are created

12. The antenna radiates the RF signal into space in the form of _____________

13. The semi conductor obtained by doping aluminium to a pure semi conductor is ______________

14. The transducer used in TV transmitter is _____________

15. In a television _____________ separates the audio signal and reproduces sound

16. In a transistor the heavily doped region is _____________

17. The device which converts the variation in brightness into electrical impulses is

Questions and Answers

1. Name the fundamental particles of an atom.

Ans:- The fundamental particles of an atom are, proton, neutron and electron.

2. Which is the negatively charged particle of an atom? What is its charge & mass?

Ans:- Electron is the negatively charged particle of an atom. Its charge= 1.6 x 10 ^-19 C and its Mass = 9.1 x 10 ^-31 kg

3. What is electric current?

Ans:- Electric current is nothing but flow of electrons.

4. What are conductors? Give an example.

Ans:- Substances which allow electric current to pass through them, are called conductors.

Examples are: Nacl, NaoH, H₂ SO₄, etc.

5.What are insulators ( bad conductors)? Give examples.

Ans:- Substances which do not allow electric current to pass through them are called insulators.

Examples are: sugar, carbon tetrachloride, chloroform etc

6. What are radio waves? Write their uses.

Ans:- Radio waves are electromagnetic waves with wavelengths greater than 0.1m.

They are used in communication systems including satellites, radars, TV and radio broadcasting.

7. What is ‘electronics’?

Ans:- Electronics is a field of physics and engineering ( both pure and applied) dealing with the design and application

of devices, usually electronic devices.

8. Mention any four electronic gadgets.

Ans:- T.V., radio, microprocessors and digital computers are four electronic gadgets

9. Mention the areas influenced by electronics.

Ans:- Electronics has influenced areas such as communication, entertainment, defense, industry and medical science

10. Mention the most recent advances in eh field of electronics

Ans:- The most recent advances in electronics includes digital circuits, micro processors, digital computers, opto-electronics, laser technology and so on

11. What are semiconductors? Give example.

Ans:- Semiconductors are the substances whose conductivity lies in between that of conductors and insulators.

Example” Germanium, Silicon, etc

12How many electrons are there in the outermost shell of atom of silicon?

Ans:- There are four electrons in the outermost shell of an atom of silicon.

13. What is called a ‘hole’?

Ans:- When an electron is removed from a covalent bond, it leaves a vacancy, equivalent to positive charge. It is called

a hole, an electron from a neighboring atom, can drop into this vacancy, leaving the neighbor with a vacancy.

In the way, the vacancy called a hole can move and serve as an additional charge carrier.

14. Distinguish between intrinsic and extrinsic semiconductors

Ans:- A pure semiconductor whose conductivity is due to equal number of holes and electrons present is

called intrinsic semiconductor

A Semiconductor whose conductivity is enhanced by the addition of minute traces of impurities

( other elements) called dopants, is called extrinsic semiconductor

15. Explain the term ‘doping’

Ans:- The conductivity of semiconductors can be enhanced by the addition of minute traces of impurilies

(other elements) called dopants. The process of adding dopants is called doping and the resulting

semiconductor is called doped semiconductor or extrinsic semiconductor.

16. Mention the types of extrinsic semiconductors and uses

Ans:- There are two types of extrinsic semiconductors depending upon the types or impurities.

They are classified as (a) N type semiconductors and (b) P type semiconductors.

These are used in the manufacture of diodes and transistors

17. Distinguish between ‘n’ type ‘p’ type semiconductors.

Ans:- P type semiconductors; If a very small amount of pentavalent impurity for example antimony (or arsenic

or phosphorous), is introduced into the crystal of germanium, four out of five electrons of each impurity atom

enter into bonds with the nearest germanium atoms, to form covalent bonds. The fifth electron is set free.

These free electrons act as current carriers.

‘N’ type semiconductors: When trivalent impurity like boron, indium, gallium is introduced into a germanium crystal, each impurity atoms takes away one electron from the neighbouring germanium atoms can fillup these holes and there will be apparent motion of holes. Thus holes act as electrons from the semiconductor and the semiconductor becomes a P- type semiconductor.

18. Name two pentavalent impurities.

Ans:- Antimony, arsenic and phosphorus are pentavalent impurities.

19. Name two trivalent impurities.

Ans:- Boron, indium, Gallium and Aluminium are trivalent impurities.

20.What is a semiconductor diode or junction diode?

Ans:- When a donor impurity is added to one side and an acceptor impurity is added to the other side of

pure semiconductor, the first side becomes n-type and other side becomes p-type. Thus a p-n junction is formed.

This is called Junction diode or a semiconductor diode.

21. What is meant by forward bias of a diode? Indicate in a figure

Ans:- When the positive terminal of cell is connected to p-side and the negative terminal to the n-side of a p-n junction,

it is said to be forward biases. The external voltage overcomes the junction potential and provides an easy path for the

flow of charge carriers across the junction. The flow of electrons from n to p and of holes from p to n, constitutes

a forward current (of the order of mA) from p to n. The device offers low resistance.

22. What is meant by reverse bias of a diode? Indicate in a figure

Ans:- When the positive terminal of a cell is connected to the n side and the negative terminal to the p side of a p-n junction it said to be reverse biased. In this case the charge carriers are repelled away from the junction and no current flows through the junction. The device offers high resistance

1. Give the circuit symbol of a diode.

Ans:-

23. State the important characteristics of diode.

Ans:- Thus p-n junction allows current to pass through prudentially in one direction only, this action is called rectifying

action and device is called ‘rectifier’.

24. Mention the applications of diode.

Ans:- Applications: A diode has a number of applications in view of its rectifying action and current detection action.

a) Diode are used to convert AC into DC b) They are used in voltage regulation systems

25. What is a transistor?

Ans:- The term ‘transistor’ is a shortened form for transistor. Transistor is a specially constructed three terminal

semiconductor device

26. Distinguish between n-p-n and p-n-p transistors

Ans:- A transistor in which one p type region is sandwiched between two n-type regions is called npn transistor.

However in pnp transistor, a n-type region is sandwiched between two p-type regions.

27. Name the three regions of a transistor

Ans:- The middle region is called the and the two and regions are called emitter and the collector

30. What are the functions of the three regions of a transistor?

Ans:- The function of the emitter is to emit electrons(in the case of npn transistor)or holes(in the case of pnp transistor)

into the base. The base controls the flow of charge carriers into the collector which collects them from the base.

31. Mention the applications of a transistor

Ans:- Transistor is used in (i) amplifier (ii) oscillator and (iii) switching circuits.

32. What is an oscillator?

Ans:- Oscillator is a device for producing electric oscillations of a desired frequency.

33. Mention the types of transistors.

Ans:- Bipolar junction transistor, Field effect transistor (FET), Metal Oxide semiconductor Field effect transistor

(MOSFET)andJunction Effect Transistor Metal Semiconductor Fields effect Transistor are some of the other transistors.

34. What is communication? Mention the technical means of communication

Ans:- In basic sense, communication means transmission of information from one person to another In a technical sense, it refers to the sending, receiving and processing of information by electrical means

Telegraph, telephone, radio, television, radar and so on are the technical means of communication

35. Mention the different types of communication systems

Ans:- Telegraph, telephone, radio, television and radar etc are different type of communication systems

36. What is radio communication?

Ans:- Radio communication is the process of sending information ( music or speech in the form of words) from one and receiving at another place, without using connecting wires

37. What is radio communication?

Ans:- Transmission of speech or music over long distances, using radio waves is calles radio broadcasting

38. Name the two major parts in radio broadcasting system

Ans:- There are two major parts in radio broadcasting system namely a transmitter and a receiver

39. Explain the principle of a radio transmitter.

Ans:- The audio (sound) information is changed into corresponding electrical signal using a transducer. Transducer is a device that converts information energy to be transmitted into electrical signal. For sound transmission, the transducer is microphone (1) this signal called audio frequency (AF) signal, being weak, is amplified by a suitable amplifier called AF amplifier (2) As AF signals, have low energy, they can not be transmitted over long distances. Therefore radio waves of suitable frequency are generated in an RF oscillator (3) These radio waves are mixed with the amplified AF signal in the mixer stage (4) In this stage, modulated. The RF wave that carries the Af signal, is called carrier. Each transmitting station has a particular carrier frequency. The modulated signal is amplified using an RF amplifier (5) and then sent to the antenna (6) The antenna radiates the RF signal into space, in from of radio waves.

40. Explain the principle of a radio receiver

Ans:- Radio waves sent by all stations, are received by the antenna (1) of the receiver. A particular station is ‘tuned in and RF signal amplified (2) the signal foes to the detector or demodulator (3) Here the AF signal is separated from the carrier. The audio signal is amplified by AF amplifier (4) and sent to a loud speaker or head phones (5)

43. Name the Indian who constructed Radio Transmitter in1923.

Ans:- Dr. S.K. Mitra constructed Radio Transmitter in 1923

44. What is a transducer?

Ans:- Transducer is a device that converts information energy to be transmitted into electrical signal

45. What is the function of detector and loud speaker in a radio receiver?

Ans:- Detector or demodulator separates AF Signal from the carrier and loud speaker converts amplified AF

signal into sound (information) energy.

46. What is the carrier frequency of i) AM ii) FM radio transmitter?

Ans: AM radio stations have carrier frequencies from about 530 to 1600 kHz, AM radio stations have much

carrier frequencies, between 88 to 108 MHz.

47. What is the function of a) Mixer B0 Antenna in a radio transmitter?

Ans:- Radio waves are missed with the amplified AF signal in the mixer. Antenna in a radio transmitter radiates the RF

signal into space in the from of radio waves.

49. What is the meaning of the word television?

Ans:- The word television, the combination of two words ‘tele’ and ‘vision’ literally means seeing at a distance.

50. What is the process of television?

Ans:- Television broadcasting is the process of transmission of transient visual image of an actual or recorded scene, along with audio signal to distance using radio waves.

51. Write a note on the principle of working of a television.

Ans:- A televion transmitter works similar to that of a radio transmitter. At the TV station, a pick up instrument ( TV camera) explores (scans) different portions of the picture or scene to be transmitted, in a particular order. The camera converts the variations in brightness in the various portions into electrical impulses (photoelectric device is used as transducer). These electrical impulses constitute the video signal. This video signal is amplified and used to amplitude modulate an RF carrier.

The sound picked up by a microphone is amplified and is used to frequency modulate an RF carrier (The frequency of this carrier is 5.5 MHz higher than that of the video carrier). Carrier frequencies in TV for various channels lie in the range from about 40 MHz to Mhz.

The two modulated carries are amplified and transmitted through the same antenna.

At the receiving end, RF signals are collected by the receiving antenna and the desired station is selected. The output corresponding to the video signal is used to control the intensity of light in a cathode ray tube; to obtain the picture transmitted. An FM receiver is used to separate the audio signal and reproduce sound.

52. Who gave the first demonstration of TV?

Ans:- The first demonstration of television, was given during 1927 by J.L. Baird (UK) and C.F. Jenkins(USA)

53. In a transistor, which part is (a) highly doped (b) moderately doped (c) lightly doped

Ans:- (a) Emitter is highly doped (b) Collector is moderately doped (c) Base is lightly doped

54. Under ordinary conditions, semiconductors behave like insulators. Why?

Ans:- Semiconductors have four valence electrons. Under ordinary conditions, these electrons are not free and

usually involved in a covalent bond. Hence they behave like insulators.

55. What is the reason for the rectifying action of a diode?

Ans:- Forward bias of the diode i.e offers low resistance causes the rectifying action of a diode.

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