General Science - Physics MCQs
Physics Objective (Multiple Choice) General Knowledge & General Science Questions & Answers for SSC-CGL, UPPSC, UPSC, NDA, CDS and UPSC Civil Services Prelims Examinations.
91. Which of the following is correct?
[A] The poles of a magnet always occur in pairs
[B] Like poles attract and unlike poles repel
[C] Both a and b
[D] None of the above
Show Answer
Correct Answer: A [The poles of a magnet always occur in pairs]
Notes:
The poles of a magnet always occur in pairs. Unlike poles attract and like poles repel.
92. Which of the following is NOT correct about the force of interaction between two poles of a magnet, as per coulomb’s law?
[A] directly proportional to the product of the pole strength
[B] directly proportional to the square of the distance r between the poles
[C] Both a and b
[D] None of the above
Show Answer
Correct Answer: B [directly proportional to the square of the distance r between the poles]
Notes:
As per coulomb’s law, the force of interaction between two poles of a magnet is directly proportional to the product of the pole strength and inversely proportional to the square of the distance r between them.
93. What is the value of Planck’s constant?
[A] 6.6 × 10–34 J s
[B] 3.6 × 10–34 J s
[C] 6.6 × 10–24 J s
[D] 6.6 × 10–17 J s
Show Answer
Correct Answer: A [6.6 × 10–34 J s]
Notes:
The value of Planck’s constant is 6.6 × 10–34 J s.
94. What is a p-n diode said to be in reverse-bias?
[A] positive terminal of the external battery is connected to the p-side
[B] positive terminal of the external battery is connected to the n-side
[C] negative terminal of the external battery is connected to the n-side
[D] None of the above
Show Answer
Correct Answer: B [positive terminal of the external battery is connected to the n-side]
Notes:
If the positive terminal of the external battery is connected to the n-side and the negative terminal of the external battery is connected to the p- side, then the p-n junction is said to be reverse biased.
95. What is the ratio of the change in collector current to the change in base current at a constant collector-emitter voltage, when the common emitter transistor is in active state, known as?
[A] Input resistance
[B] Output resistance
[C] Current amplification factor
[D] None of the above
Show Answer
Correct Answer: C [Current amplification factor]
Notes:
Current amplification factor β: This is defined as the ratio of the change in collector current to the change in base current at a constant collector-emitter voltage (VCE) when the transistor is in active state.
96. Which type of semiconductor do we get when pure silicon is doped with a group-3 element?
[A] n-type semiconductor
[B] p-type semiconductor
[C] Intrinsic semiconductor
[D] None
Show Answer
Correct Answer: B [p-type semiconductor]
Notes:
If silicon (or germanium) is doped with a trivalent (three electrons in the outermost shell) atom like boron, aluminium, gallium or indium, three valence electrons form covalent bonds with three silicon atoms and deficiency of one electron is created. Such a semiconductor is said to be a p- type semiconductor.
97. What are the majority charge carriers in p-type semiconductors?
[A] electrons
[B] holes
[C] equal concentration of holes and electrons
[D] None of the above
Show Answer
Correct Answer: B [holes]
Notes:
Note that in a p-type semiconductor, more holes are created due to addition of acceptor impurity than by breaking covalent bonds due to thermal energy at room temperature. Hence, the net concentration of holes is significantly greater than that of electrons. That is, in a p-type semiconductor, the holes are the majority charge carriers.
98. What is the charge of a p-type semiconductor?
[A] Positive
[B] Negative
[C] Neutral
[D] None of the above
Show Answer
Correct Answer: C [Neutral]
Notes:
The number of free electrons is exactly equal to the total number of holes and positively charged ions and a semiconductor, whether intrinsic or doped, is electrically neutral
99. What is the barrier potential for Germanium?
[A] 0.3 V
[B] 0.7 V
[C] 1 V
[D] 1.7 V
Show Answer
Correct Answer: A [0.3 V]
Notes:
The barrier potential is characteristic of the semiconductor material. It is about 0.3 V for Germanium.
100. Which of these is used as a material for making semiconductor devices?
[A] Silicon
[B] Germanium
[C] Gallium Arsenide
[D] All of the above
Show Answer
Correct Answer: D [All of the above]
Notes:
Semiconductor raw materials include germanium, gallium arsenide, silicon carbide.
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