Grade 12 : Physics - Semiconductors (Set 1)

Question 1

In an intrinsic semiconductor at thermal equilibrium, which relation correctly compares the electron density ($n_e$), hole density ($n_h$), and intrinsic carrier density ($n_i$)?

Accepted Answer

C) $n_e = n_h = n_i$

Answer

A) $n_e > n_h$

Answer

B) $n_e < n_h$

Answer

D) $n_e = 0$

Question 2

What type of semiconductor is formed when pure Silicon is doped with a trivalent impurity such as Boron?

Accepted Answer

B) p-type semiconductor

Answer

A) n-type semiconductor

Answer

C) Intrinsic semiconductor

Answer

D) Insulator

Question 3

What happens to the width of the depletion layer in a p-n junction diode under forward bias?

Accepted Answer

B) Decreases

Answer

A) Increases

Answer

C) Remains unchanged

Answer

D) Expands to infinity

Question 4

The energy band gap ($E_g$) for Silicon at room temperature is approximately:

Accepted Answer

B) 1.1 eV

Answer

A) 0.7 eV

Answer

C) 3.0 eV

Answer

D) 0.0 eV

Question 5

If an alternating current input signal of frequency 50 Hz is fed into a full-wave rectifier, what is the fundamental output ripple frequency?

Accepted Answer

C) 100 Hz

Answer

A) 25 Hz

Answer

B) 50 Hz

Answer

D) 200 Hz

Question 6

Which of the following elements acts as a pentavalent donor impurity in Silicon?

Accepted Answer

C) Phosphorus

Answer

A) Aluminium

Answer

B) Boron

Answer

D) Indium

Question 7

According to the mass action law for a semiconductor in thermal equilibrium, which equation holds true?

Accepted Answer

B) $n_e \cdot n_h = n_i^2$

Answer

A) $n_e \cdot n_h = n_i$

Answer

C) $n_e \cdot n_h = 2n_i$

Answer

D) $\frac{n_e}{n_h} = n_i^2$

Question 8

A Zener diode is specially designed to operate continuously in which region of its voltage-current characteristics?

Accepted Answer

C) Reverse breakdown region

Answer

A) Forward biased active region

Answer

B) Unbiased cut-off region

Answer

D) Saturation region

Question 9

Why is a photodiode preferably operated in reverse bias mode to detect light signals?

Accepted Answer

B) Fractional change in minority carrier current is much easier to measure

Answer

A) Forward current is too small to measure

Answer

C) Reverse bias increases the barrier potential to infinity

Answer

D) Reverse bias prevents thermal carrier generation

Question 10

What is the output logic level ($Y$) of a two-input NAND gate when both inputs $A$ and $B$ are set to logic 1?

Accepted Answer

A) 0

Answer

B) 1

Answer

C) High impedance

Answer

D) Undefined

Question 11

How does the electrical resistance of an intrinsic semiconductor change as its temperature increases?

Accepted Answer

B) Decreases

Answer

A) Increases linearly

Answer

C) Remains constant

Answer

D) Increases exponentially

Question 12

In an n-type semiconductor, what are the majority and minority charge carriers respectively?

Accepted Answer

B) Electrons and Holes

Answer

A) Holes and Electrons

Answer

C) Electrons and Protons

Answer

D) Positrons and Electrons

Question 13

What is the maximum theoretical efficiency ($ \eta$) of a half-wave rectifier?

Accepted Answer

A) 40.6%

Answer

B) 81.2%

Answer

C) 50.0%

Answer

D) 100.0%

Question 14

Which basic logic gate produces an output of 1 ONLY when all of its inputs are 1?

Accepted Answer

C) AND gate

Answer

A) OR gate

Answer

B) NOR gate

Answer

D) XOR gate

Question 15

To emit light efficiently, a Light Emitting Diode (LED) must be operated under which condition?

Accepted Answer

C) Forward bias

Answer

A) Reverse bias

Answer

B) Zero bias

Answer

D) Reverse breakdown region

Question 16

The total electrical conductivity ($\sigma$) of a semiconductor containing electron density $n_e$, hole density $n_h$, and mobilities $\mu_e, \mu_h$ is expressed as:

Accepted Answer

A) $\sigma = e(n_e \mu_e + n_h \mu_h)$

Answer

B) $\sigma = e(n_e \mu_e - n_h \mu_h)$

Answer

C) $\sigma = \frac{e}{n_e \mu_e + n_h \mu_h}$

Answer

D) $\sigma = e n_i (\mu_e - \mu_h)$

Question 17

When a p-n junction diode is subjected to a reverse bias, the total height of the potential barrier:

Accepted Answer

B) Increases

Answer

A) Decreases

Answer

C) Drops to zero

Answer

D) Remains unchanged

Question 18

In which class of materials do the conduction band and valence band overlap with each other?

Accepted Answer

C) Conductors (Metals)

Answer

A) Insulators

Answer

B) Semiconductors

Answer

D) Superconductors at room temperature

Question 19

Under standard operational conditions, a solar cell generates electric current under which external bias state?

Accepted Answer

C) Unbiased condition

Answer

A) Strong forward bias

Answer

B) Reverse bias

Answer

D) Zener breakdown bias

Question 20

For a 2-input NOR gate, what is the output state when input $A = 1$ and input $B = 0$?

Accepted Answer

B) 0

Answer

A) 1

Answer

C) Oscillating

Answer

D) High Impedance