Grade 12 : Physics - Semiconductors (Set 2)

Question 1

1. What are the primary charge carriers responsible for electrical conduction in an pure intrinsic semiconductor at room temperature?

Accepted Answer

C) Both free electrons and holes in equal numbers

Answer

A) Free electrons only

Answer

B) Holes only

Answer

D) Positive donor ions only

Question 2

2. Which of the following dopants acts as a donor impurity when added to pure silicon to create an n-type semiconductor?

Accepted Answer

B) Phosphorus

Answer

A) Boron

Answer

C) Aluminum

Answer

D) Indium

Question 3

3. When pure Germanium is doped with a trivalent element such as Aluminum, what type of semiconductor material is produced?

Accepted Answer

B) p-type semiconductor

Answer

A) n-type semiconductor

Answer

C) Intrinsic semiconductor

Answer

D) Superconductor

Question 4

4. In a p-type semiconductor material, which particles serve as the majority charge carriers?

Accepted Answer

B) Holes

Answer

A) Free electrons

Answer

C) Pentavalent donor ions

Answer

D) Protons

Question 5

5. What happens to the width of the depletion layer in a p-n junction diode when it is forward biased?

Accepted Answer

B) It decreases

Answer

A) It increases

Answer

C) It remains constant

Answer

D) It expands to cover the whole crystal

Question 6

6. How does the potential barrier of a p-n junction respond when the diode is reverse biased?

Accepted Answer

C) It increases

Answer

A) It decreases to zero

Answer

B) It remains unaffected

Answer

D) It oscillates continuously

Question 7

7. What is the primary operational application of a Zener diode in electronic power supplies?

Accepted Answer

B) Voltage regulator

Answer

A) High frequency signal amplifier

Answer

C) Full-wave current rectifier

Answer

D) Solar optical generator

Question 8

8. An alternating current (AC) signal with a frequency of 50 Hz is fed into a full-wave rectifier circuit. What is the fundamental ripple frequency of the output voltage?

Accepted Answer

C) 100 Hz

Answer

A) 25 Hz

Answer

B) 50 Hz

Answer

D) 200 Hz

Question 9

9. Under which external bias condition is a Light Emitting Diode (LED) operated to produce spontaneous light emission?

Accepted Answer

B) Forward bias

Answer

A) Reverse bias

Answer

C) Zero bias

Answer

D) Zener breakdown bias

Question 10

10. Why is a photodiode usually operated under reverse bias mode for detecting optical radiation?

Accepted Answer

A) The fractional change in minority carrier current is easily measurable

Answer

B) The total current becomes zero under light illumination

Answer

C) Forward bias damages the optical window of the diode

Answer

D) The potential barrier disappears entirely

Question 11

11. How does the electrical resistivity of an intrinsic semiconductor change as its temperature is increased?

Accepted Answer

B) It decreases

Answer

A) It increases linearly

Answer

C) It remains constant

Answer

D) It increases exponentially

Question 12

An intrinsic silicon crystal has an intrinsic carrier concentration of $n_i = 1.5 imes 10^{16}m^{-3}$. After doping, the electron concentration increases to $n_e = 4.5 imes 10^{22}m^{-3}$.

12. Using the mass action law $n_e \cdot n_h = n_i^2$, determine the hole concentration $n_h$ in the doped silicon.

Accepted Answer

A) $5.0 	imes 10^{9}m^{-3}$

Answer

B) $1.0 	imes 10^{10}m^{-3}$

Answer

C) $3.0 	imes 10^{38}m^{-3}$

Answer

D) $6.75 	imes 10^{38}m^{-3}$

Question 13

13. Which digital logic gate generates an output of 1 ONLY when both of its inputs are 0?

Accepted Answer

C) NOR gate

Answer

A) AND gate

Answer

B) OR gate

Answer

D) NAND gate

Question 14

14. What is the output $Y$ of a 2-input NAND gate when both inputs are set to high level ($A = 1$ and $B = 1$)?

Accepted Answer

A) 0

Answer

B) 1

Answer

C) Fluctuating

Answer

D) High voltage equivalent to $A+B$

Question 15

15. What is the characteristic range of energy band gap ($E_g$) for an electrical insulator material?

Accepted Answer

C) $E_g > 3	ext{ eV}$

Answer

A) $E_g = 0	ext{ eV}$

Answer

B) $E_g < 0.2	ext{ eV}$

Answer

D) $E_g = 1.1	ext{ eV}$

Question 16

16. In an unbiased, isolated p-n junction, in which direction does the initial diffusion current flow?

Accepted Answer

B) From p-side to n-side

Answer

A) From n-side to p-side

Answer

C) From p-side to external ground

Answer

D) From n-side to external ground

Question 17

17. An AC signal of frequency 60 Hz is supplied to a half-wave rectifier circuit. What is the fundamental output frequency of the rectified DC current?

Accepted Answer

B) 60 Hz

Answer

A) 30 Hz

Answer

C) 120 Hz

Answer

D) 0 Hz

Question 18

18. Which of the following substances exhibits a negative temperature coefficient of resistance ($\alpha < 0$)?

Accepted Answer

C) Silicon

Answer

A) Copper

Answer

B) Aluminum

Answer

D) Silver

Question 19

19. Which logic gate is represented by the Boolean expression $Y = \overline{A + B}$?

Accepted Answer

C) NOR gate

Answer

A) AND gate

Answer

B) NAND gate

Answer

D) XOR gate

Question 20

20. When light photons with energy $h u > E_g$ strike a solar cell junction, what fundamental mechanism generates electrical energy?

Accepted Answer

A) Generation of electron-hole pairs followed by separation due to the junction electric field

Answer

B) Annihilation of existing charge carriers in the neutral zones

Answer

C) Direct thermal breakdown of covalent bonds without charge separation

Answer

D) External breakdown current supplied by a battery