Chapter-17
Electronics
Learning Card-1
Choose the correct answer:
1. The impurity element which can be obtained p-type impurity is?
a. Phosphorous b. Arsenic c. Antimony d. Aluminum
2. The electronic component which is used in voltage regulator is.
a. Diode b. Transistor c. super conductor d. Intrinsic semiconductor
3. Under the reverse biasing of a diode, the p-type and n-type semiconductors are connected to these terminals of a battery respective.
a. +ve and -ve terminals b. -ve and +ve terminals
c. -ve and -ve terminals d. +ve and +ve terminals
4. If IE is emitter current, IB is box current and IC is collector current, their relation is given by.
a. IE= IB = IC b. IE= IB + IC c. IE= IB - IC d. IB= IE + IC
5. The temperature at which the resistance of a conductor is zero.
a. Ideal temperature b. Critical Temperature
c. Absolute Temperature d. All the above
Question and Answers:
1. What is the value of conducting of a semi conductor at zero kelvin?
Zero.
2. How does the resistance of a semiconductor vary with temperature?
The resistance of a semiconductor decreases with increase in temperature.
3. Which is the most suitable semiconductor in electronics?
Silicon.
4. What is an extrinsic semiconductor?
A doped semiconductor is called an extrinsic semiconductor.
5. What is doping of a semiconductor?
It is a process of adding impurity atoms to a pure semiconductor crystal to increase its electrical conductivity.
6. What are dopants?
The impurity atoms added to a pure semiconductor to increase conductivity are called dopants.
7. Name the types of extrinsic semiconductors.
The two types of extrinsic semiconductors are N-type and P-type semiconductors.
8. Which are the dopants used to form P-type semiconductor?
Boron, Indium, Gallium, Aluminum.
9. Which are the dopants used to form N-type semiconductor?
Arsenic, Antimony, Phosphorous.
10. What is a hole?
The hole is a set of positive charge which is produced when an electron breaks away from a covalent bond in a semiconductor.
11. What are the types of semiconductors?
a) Intrinsic semiconductor b) Extrinsic semiconductor
12. What is a PN juction?
The junction between a P-type and N-type semiconductor is such way that the crystal structure remains continuous at the boundary is called an PN junction.
13. When a PN junction is said to be forward biased?
PN junction is said to be forward biased when p-side of the junction is connected to positive terminal of the battery and n side of the junction is connected to negative terminal of the battery.
14. When a PN junction is said to be reverse baised?
PN junction is said to be reverse based if P-region is connected to negative terminal and N-region is connected to positive terminal of the battery.
15. Which are the two important charectristic of the forward based PN junction
a. Conductivity is high. b. Resistance is low.
16. Which are the two important charectristic of the reverse based PN juction.
a) Conductivity is low. b) Resistance is high.
17. Why, in a reverse based junction small current flows?
Due to minority charge carriers on either side of PN Junction.
18. Give the Circuit Symbol of the diode.
19. What is rectification?
The process of coverting alternative current to direct current is known as rectification.
20. Why diode is called as rectifier?
It conducts only in one direction hence it is called rectifier.
21. What is a transistor?
A transistor is a semiconductor device consisting of 2 PN junctions back to back.
22. Name three regions of transistor.
emitter, base, collector.
23. Name dopoing concentration of each region of a transistor?
emitter - heavily doped
base - lightly doped
collector - moderately doped.
24. Mention function of each regions of a transistor.
emitter - emits majority charge carriers to the base
base - controls the flow of majority charge carriers.
collector - collects the majority charge carriers from the base.
25. Mention the size of each regions of a transistor.
emitter - Moderate in size
base - very thin
collector - large in size.
26. Draw a neat diagram of a forward biased diode.
27. Draw a neat diagram of a reverse biased diode.
28. Mention any one application of diode.
It is used to convert AC in to DC.
29. Draw the circuit symbol of NPN and PNP transistor.
30. Draw simple transistor circuit
31. Mention the applications of transistor.
It is used in
1. Amplifiers. 2. Oscillators. 3. Switching circuits.
32. What is super conductors?
The property by virtue of which certain materials show almost zero resistance at a very low temperature is called super conductivity.
33. Define critical temperature.
The temperature below which a material becomes a super conductor is called critical temperature (Tc)
34. Mention any one used of super conductors.
They are used in powerful electromagnets.
Chapter-17
Electronics
Learning Card-2
Choose the correct answer:
1. When a trivalent impurity is added to pure semiconductor, the majority charge carries in so obtained impure semiconductor
(a) electrons (b) holes (c) both electrons and holes (d) neither electrons nor holes
2. A major difference between a conductor and a diode in working is
(a) Both of them conducts electricity
(b) Conductors allows current in any direction but diode allows only in one direction
(c) Diode cannot control the flow of current where as conductor can
(d) Conductor allows current only in one direction but diode allows in two directions also
3. The critical temperature of mercury is 4.2K. It means the current given to mercury
(a) can flow for few microseconds (b) can flow for long time
(c) is stopped at very short intervals (d) always increases before input is given
Question and Answers:
1. Why at low termperatures Germanium and Silicon behaves as insulators?
At low termperatures (0K) the atoms of silicon and germanium have 4 electrons each in their outer most shell. These electrons are involved in covalent bonding and are not free. Hence these elements should behave like insulators.
2. How does conductivity of a semiconductor change with temperature?
The conductivity of a semiconductor increases with raise of temperature because more covalent bonds in semiconductor get broken with the rise of temperature providing more number of electrons and holes as current carriers.
3. Differentiate between N type and P type semi conductors?
| n-type semiconductors | p-type semiconductors |
| 1. It is prepared by doping with a pentavalent impurity. | 1. It is prepared by doping with a trivalent impurity. |
| 2. The impurity atoms added will donate electrons. | 2. The impurity atoms added will accept electrons. |
| 3. The majority of charge carriers are electrons. | 3. The majority of charge carriers are holes. |
4. Differentiate between npn transistor and pnp transistor.
| npn transistor | pnp transistor |
| When one p side is sandwiched between two n regions, a npn transistor is formed | When one n side region is sandwiched between two p regions a pnp transistor is formed |
| The function of emitter, is to emit electrons to the base | The function of emitter is to emit holes to the base |
5. Differentiate between intrinsic and extrinsic semi conductors?
| Intrinsic semiconductor | Extrinsic semiconductor |
| They are pure semiconductor | They are formed when minute traces of other elements are added to intrinsic semiconductor |
| They have equal number of holes and electrons | In an n-type semiconductor, electrons are majority carriers and holes are majority carriers. In a p-type semiconductor, electrons are minority carriers and holes are majority carriers. |
| Their conductivity is very small | The conductivity of the semiconductor is more |
| Eg: Ge, Si, | Eg: n-type and p-type semiconductor. |
Chapter-17
Electronics
Learning Card-3
Choose the correct answer:
1. The following in diagram of a biased transistor. Identify the mistake in the connection.
a) Emitter junction is wrongly biased
b) Collector junction is wrongly biased
c) Both emitter region and collector region are wrongly connected
d) The transistor itself is wrongly connected
2. The property of the base in a transistor is
a) Less thickness - highly doped b) more thickness - highly doped
c) Less thickness - highly doped d) More thickness - lightly doped
3. Which of the following denotes the link among Ac, diode and DC. in its proper order.
4. When the thickness of the potential barrier is increased the resistance for the flow of current in the diode decreased. This happens in
a) Reverse biasing b) Forward biasing c) Doping d) Amplification
5. In the input region of a transistor a variation of 10mV is observed as a variation of 25 mV in the out put region. For this to happen in a transistor.
a) Emitter region is forward biased
b) Collector region is reverse biased
c) Emitter region is forward biased and collector region is reverse biased
d) Emitter region is reverse biased and collector region is forward biased.
Question and Anwers:
1. How is a P-type semiconductor formed?
If a trivalent impurity like boron, indiuem, gallium, aluminium is introduced in the germanicum crystal, each impurity atom takes away one electron from the neighbouring germainium atoms to form covalent bonds this results in the creation of holes. electrons from neighbouring atoms can fill up holes and their will be apparent motion of holes. Thus holes act as current carriers. The added trivalent impurity accepts electrons from the semiconductor and the semiconductor behave like P-type semi conductor.
2. How is an N-type semiconductor formed?
If a very small amount of pentavalent impurity for ex . Antimony or arsenic or phosphorous, is intoduced into the crystal of geamanium, four out of five electrons of each impurity atom enter in to bonds with the nearest germanium atoms, to from covalent bonds The fifth electron is set free these free electrons act as current carries. The added pentavalent impurity donates electrons to the semiconductor and the semiconductor becomes N-type semiconductor
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