# NEET

Explore popular questions from Electronic Devices for NEET. This collection covers Electronic Devices previous year NEET questions hand picked by experienced teachers.

## Biology

Electronic Devices

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Q 1. In a pn junction, the barrier potential offers opposition to only

majority carriers in both regions

B

minority carriers in both regions

C

electrons in n-region

D

holes in p-region

##### Explanation

When a semiconductor diode is formed, a depletion layer is formed across its junction. This depletion layer has negative charge in p-type crystal and positive charge in n-type crystal, thus acts as a potential barrier for charge carriers. In p-region, holes are majority carriers (electrons are minority carriers) and in n- region electrons are majority carriers (holes are minority carriers). When an electron (majority carrier) from n-region, tries to cross the junction, the negative charge of the barrier (in p-region) opposes the electron (whereas helps the hole) and electron is stopped by this barrier's negative plate. Same happens with a hole in p-region. Hence, the potential barrier offers opposition to majority carriers in both regions.

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Q 2. Let {tex}n_p{/tex} and {tex}n_e{/tex} be the number of holes and conduction electrons respectively in a semiconductor. Then

A

{tex}n_p{/tex} > {tex}n_e{/tex} in an intrinsic semiconductor

B

{tex}n_p{/tex} = {tex}n_e{/tex} in an extrinsic semiconductor

{tex}n_p{/tex} = {tex}n_e{/tex} in an intrinsic semiconductor

D

{tex}n_e{/tex} > {tex}n_p{/tex} in an extrinsic semiconductor

##### Explanation

In intrinsic semiconductors, the creation and liberation of one free electron by the thermal energy has created one hole. Thus in intrinsic semiconductors {tex}n_p{/tex} = {tex}n_e{/tex}.

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Q 3. The figure represents a

NOR gate

B

OR gate

C

AND gate

D

NOT gate

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Q 4. At zero degree kelvin a piece of germanium

A

becomes semiconductor

B

becomes good conductor

D

has maximum conductivity

##### Explanation

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Q 5. Electronic configuration of germanium is {tex} 2,8,18 {/tex} and {tex} 4 . {/tex} To make it an extrinsic semiconductor, a small quantity of antimony is added.

A

The material obtained will be {tex} n {/tex} -type semiconductor in which electrons and holes are equal in number.

The material obtained will be {tex} n {/tex} -type semiconductor which has more electrons than holes at room temperature

C

The material obtained will be {tex} n {/tex} -type semiconductor which has less electrons than holes at room temperature

D

The material obtained will be {tex} p {/tex} -type semiconductor

##### Explanation

Antimony is a fifth group impurity and is therefore a donor of electrons.

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Q 6. A semiconductor is cooled from room temperature. Its resistance will

A

decrease

increase

C

first decrease and then increase

D

not change

##### Explanation

A semiconductor has negative temperature coefficient of resistance . As Temperature increases, semiconductor resistance decreases. Therefore when a semiconductor is cooled, its resistance will increase

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Q 7. Least doped region in a transistor is

A

emitter

B

collector

C

either emitter or collector

base

##### Explanation

The lightly doped region is called the base which is sandwiched between emitter and the collector.