ECET 299 Active Devices PRACTICE 1 Student Gradebook Exam Questions with Answers

9/6/2016 Student Gradebook Exam




Grading Summary

These are the automatically computed
results of your exam. Grades for essay Date Taken: 9/6/2016
questions, and comments from your Time Spent: 03 min , 50 secs
instructor, are in the "Details" section Points Received: (32%)
below.

Question Type: # Of Questions: # Correct:
Multiple Choice 25 8


Grade Details ­ All Questions

1. Question : (TCO 2) The majority carriers in an n­type semiconductor are
Student Answer: negative ions. (Charge is carried by electrons (n­type) or holes (p­type) in
semiconductors.)
positive ions. (Charge is carried by electrons (n­type) or holes (p­type) in
semiconductors.)
electrons. (Electrons are the charge carries for p­type semiconductors.)
holes. (This is correct. Electrons carry charge in n­type semiconductors.)
Instructor Explanation: An n­type semiconductor is formed by introducing impurities with five valence
electrons into a silicon base. Because silicon has four covalent bonds, this creates a
surplus of electrons.
See Boylestad and Nashelsky, Chapter 1.5.

Points Received: 1 of 1
Comments:



2. Question : (TCO 2) A forward­biased diode
Student Answer: conducts current. (This is correct; the diode is “on” so current flow is
enabled.)
blocks current. (This is the condition for a reverse­bias diode.)
rectifies current. (Only partially correct, because when an AC signal is
applied, the diode is alternately conducting and blocking current flow.)
amplifies. (The diode provides no amplification.)
Instructor Explanation: The condition of a forward bias describes turning a diode on to allow current flow. In
the reverse bias condition, no current flows. See Boylestad and Nashelsky, Chapter
1.5.

Points Received: 0 of 1
Comments:



3. Question :
(TCO 2) For the following figure, , , the Zener is ideal

with . What is the minimum value of to keep the Zener in
breakdown?




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, 9/6/2016 Student Gradebook Exam




Student Answer: 60 Ω (This is correct as shown by solving the formula for RL.)
24 Ω (This is an error caused by adding the values in the denominator
instead of subtracting.)
140 Ω (This error is caused by using E instead of Vz in the numerator.)
120 Ω (This is just wrong.)
Instructor Explanation: For the case of a fixed voltage and variable load resistor, the formula for determining
the value of the load resistor is: RL = (R1VZ)/(E – VZ)= [(80 Ω)(8.6V)]/(20V – 8.6V) =
60 Ω. See Boylestad and Nashelsky, Chapter 2.10.

Points Received: 1 of 1
Comments:



4. Question : (TCO 2) What is beta (β)?
Student Answer: The ratio of the collector current to the emitter current (This is incorrect; beta
is the ratio of collector to base current.)
The ratio of the collector current to the base current (This is the definition of
beta.)
The ratio of the emitter current to the base current (This is incorrect; beta is
the ratio of collector to base current.)
The ratio of the emitter current to the collector current (This is incorrect; beta
is the ratio of collector to base current.)
Instructor Explanation: Beta is used to describe the ratio of collector to base current in the dc mode of a
common­emitter bipolar junction transistor. For practical devices, this value ranges
from about 50 to 400, with most devices having a value of about 200. See Boylestad
and Nashelsky, Chapter 3.6.

Points Received: 1 of 1
Comments:



5. Question : (TCO 2) In the common­emitter configuration for a bipolar junction transistor,
Student Answer: the collector base is forward biased and the base emitter is reverse biased.
(This is the case for a common­collector configuration.)
the base emitter is forward biased and the collector base is reverse biased.
(This correctly defines the common­emitter configuration.)
the base emitter is forward biased and the collector base is forward biased.
(This is incorrect, because both junctions cannot have the same biasing in this
configuration.)
the collector base is reverse biased and the base emitter is reverse biased.
(This is incorrect, because both junctions cannot have the same biasing in this
configuration.)
Instructor Explanation: The common­emitter configuration is the most utilized configuration for BJT
transistors. In this configuration, the emitter is common to both the input and output

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