Semiconductors; intrinsic and extrinsic; the p-n junction — practice questions

Question 1 · difficulty L1 · recall

A semiconductor has electrical conductivity that is typically

• A. between that of conductors and insulators
• B. always greater than copper
• C. exactly zero at all temperatures
• D. independent of temperature and doping

Question 2 · difficulty L1 · understanding

In an intrinsic semiconductor, the number of free electrons is

• A. much greater than holes
• B. equal to the number of holes
• C. much smaller than holes
• D. always zero

Question 3 · difficulty L2 · understanding

Doping silicon with a pentavalent impurity produces

• A. a p-type semiconductor
• B. an intrinsic semiconductor
• C. an n-type semiconductor
• D. a perfect insulator

Question 4 · difficulty L2 · application

Doping silicon with a trivalent impurity produces

• A. an n-type semiconductor
• B. a metal with no holes
• C. an intrinsic crystal
• D. a p-type semiconductor

Question 5 · difficulty L2 · understanding

In a semiconductor $p$-n diode, the doping concentrations on $p$-side and $n$-side are $10^{15}$ atoms $/ \mathrm{cm}^3$ and $10^{18}$ atoms $/ \mathrm{cm}^3$, respectively. Which one of the following statements is true?

• A. Widths of depletion region on either side of the interface are equal
• B. The depletion region width is more on p -side compared to that in n -side
• C. The depletion region width is more on $n$-side compared to that in $p$-side
• D. No depletion region forms because of unequal doping concentrations on p and n -sides

Question 6 · difficulty L2 · understanding

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason $\mathbf{R}$ Assertion A : A diode under reverse-biased condition provides very small current which is nearly independent of voltage until a critical limit at which the current increases drastically. Reason R : Below the critical voltage limit, only majority charge carriers flow which increases drastically above critical voltage. choose the correct answer from the options given below

• A. Both $\mathbf{A}$ and $\mathbf{R}$ are true and $\mathbf{R}$ is the correct explanation of $\mathbf{A}$
• B. Both $\mathbf{A}$ and $\mathbf{R}$ are true but $\mathbf{R}$ is NOT the correct explanation of $\mathbf{A}$
• C. A is true but $\mathbf{R}$ is false
• D. A is false but $\mathbf{R}$ is true

Question 7 · difficulty L2 · understanding

Consider a circuit consisting of a capacitor $(20 \mu \mathrm{~F})$, resistor $(100 \Omega)$ and two identical diodes as shown in figure. The resistance of diode under forward biasing condition is $10 \Omega$. The time constant of the circuit is $\alpha \times 10^{-3} \mathrm{~s}$. The value of $\alpha$ is $\_\_\_\_$

• A. 2.2
• B. 2.0
• C. 2.1
• D. 2.4

Question 8 · difficulty L2 · understanding

The output voltage in the following circuit is (Consider ideal diode case)

• A. 0 V
• B. +5 V
• C. −5 V
• D. 10 V

Question 9 · difficulty L2 · understanding

What is the current through the battery in the circuit shown below?

• A. 1.5 A
• B. 0.25 A
• C. 1.0 A
• D. 0.5 A

Question 10 · difficulty L2 · understanding

Which of the following circuits represents a forward biased diode? Choose the correct answer from the options given below:

• A. (C) and (E) only
• B. (A) and (D) only
• C. (B), (D) and (E) only
• D. (B), (C) and (E) only