Semiconductor

NEET Physics · 93 questions · Page 6 of 10 · Click an option or "Show Solution" to reveal answer

Q51

In forward biasing of the p-n junction

A the positive terminal of the battery is connected to p-side and the depletion region becomes thick.

B the positive terminal of the battery is connected to n-side and the depletion region becomes thin.

C the positive terminal of the battery is connected to n-side and the depletion region becomes thick.

D the positive terminal of the battery is connected to p-side and the depletion region becomes thin.

Correct Answer

Option D

Solution

In forward biasing, the positive terminal of the battery is connected to p-side and the negative terminal to n-side of p-n junction.

The forward bias voltage opposes the potential barrier.

Due to it, the depletion region becomes thin.

Q52

If a small amount of antimony is added to germanium crystal

A it becomes a p-type semiconductor

B the antimony becomes an acceptor atom

C there will be more free electrons than holes in the semiconductor

D its resistance is increased

Correct Answer

Option C

Solution

If a small amount of antimony is added to germanium crystal, crystal becomes n-type semiconductor.

Hence, there will be more free electrons than holes.

Q53

A transistor is operated in common emitter configuration at V C = 2 V such that a change in the base current from 100

\mu

A to 300

\mu

A produces a change in the collector current from 10 mA to 20 mA. The current gain is

A 50

B 75

C 100

D 25

Correct Answer

Option A

Solution

Current gain, $\beta$ =

{{\Delta {I_C}} \over {\Delta {I_B}}}

{{\left( {20 - 10} \right) \times {{10}^{ - 3}}} \over {\left( {300 - 100} \right) \times {{10}^{ - 6}}}}

= 50

Q54

Symbolic representation of four logic gates are shown as Pick out which ones are for AND, NAND and NOT gates, respectively

A (ii), (iii) and (iv)

B (iii), (ii) and (i)

C (iii), (ii) and (iv)

D (iii), (iv) and (ii)

Correct Answer

Option D

Solution

AND, NAND and NOT gates are (iii), (iv) and (ii) respectively.

Q55

The following figure shows a logic gate circuit with two inputs A and B and the output Y. The voltage waveforms of A, B and Y are as given. The logic gate is

A NOR gate

B OR gate

C AND gate

D NAND gate

Correct Answer

Option D

Solution

It is clear from given logic circuit, that out put Y is low when both the inputs are high, otherwise it is high.

Thus logic circuit is NAND gate.

Q56

For transistor action (1) Base, emitter and collector regions should have similar size and doping concentrations. (2) The base region must be vety thin and lightly doped. (3) The emitter-base junction is forward biased and base-collector junction is reverse biased. (4) Both the emitter-base junction as well as the base-collector junction are forward biased. Which one of the following pairs of statements is correct?

A (4) and (1)

B (1) and (2)

C (2) and (3)

D (3) and (4)

Correct Answer

Option C

Solution

For transistor action, the base region must be very thin and lightly doped.

Also, the emitter-base junction is forward biased and base-collector junction is reverse biased.

Q57

A common emitter amplifier has a voltage gain of 50, an input impedance of 100

\Omega

and an output impedance of 200

\Omega

. The power gain of the amplifier is

A 500

B 1000

C 1250

D 50

Correct Answer

Option C

Solution

Voltage gain= $\beta$ × Impedance gain $\Rightarrow$ 50 = β × (200/100) $\Rightarrow$ $\beta$ = 25 Power gain = $\beta$ × Voltage gain = 25 × 50 = 1250

Q58

Which one of the following statement is false ?

A Pure Si doped with trivalent impurities gives a p-type semiconductor.

B Majority carries in a n-type semiconductor are holes.

C Minority carries in a p-type semiconductor are electrons.

D The resistance of intrinisic semiconductor decreases with increase of temperature.

Correct Answer

Option B

Solution

In a n-type semiconductors, electrons are majority carriers and holes are minority carriers.

Q59

The device that can act as a complete electronic circuit is

A junction diode

B integrated circuit

C junction transistor

D zener diode

Correct Answer

Option B

Solution

Integrated circuit can act as a complete electronic circuit.

Q60

Which one of the following bonds produces a solid that reflects light in the visible region and whose electrical conductivity decreases with temperature and has high melting point ?

A metallic bonding

B van der Waal's bonding

C ionic bonding

D covalent bonding

Correct Answer

Option A

Solution

In case of metal, conductivity decreases with increase in temperature and metal has high melting point.

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