CE164 FOUNDATIONS OF ELECTRONICS
Creation date:2024-06-18 14:59:19
FOUNDATIONS OF ELECTRONICS
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FOUNDATIONS OF ELECTRONICS II
Time allowed: TWO hours (exam time) + ONE hour to allow for submission time (total
THREE hours)
(Please see your exam timetable or check on FASER for the deadline to upload your answers)
The times shown on your timetable are in British Summer Time (BST) (GMT+1). Please check
online for a conversion to your local time if you will be undertaking your assessment outside the
United Kingdom
Candidates are permitted to use:
Calculator: Casio FX-83GT PLUS/X, and Casio FX-85GT PLUS/X only
The paper consists of TWO MAIN QUESTIONS. Candidates must answer ALL questions.
The questions ARE NOT of equal weight.
The percentages shown in brackets provide an indication of the proportion of the total marks
for the PAPER which will be allocated.
If you have a query with the content of this exam paper please use the revision FAQ
Forum on the module’s Moodle page. Your academic will be available to answer any
queries in real-time.
If you have a technical problem with FASER, or any other query, please go to Exams
Website to find contact details of the teams that can help you.
Please note that the time allocated for this assessment includes time for you to download this
question paper and answer paper and to upload your answers to FASER.
Please allow at least 30 minutes at the end of your exam time to upload your work. Once you
have completed the assessment do not leave it to the last minute to upload.
Please save your work throughout the examination to avoid losing your work.
Please do not communicate with any other candidate in any way during this assessment.
Your response must be your own work. Procedures are in place to detect plagiarism and
collusion.
CE164-4-SP 2
Candidates must answer all questions and must show all work.
As a memory aid, various equations are shown in the last two pages of this
paper.
Question 1
(a) Calculate the capacitance between a pair of 4.0 cm diameter round plates immersed in
oil if the plates are separated by 0.25 mm. For oil, the dielectric constant is r = 4.0.
(b) Examine the circuit in Figure 1.b.
i) Plot the curves for VC, IC, and VR in terms of multiples of the time constant when
the switch is moved to position 1. In your plots include the maximum and
minimum values for each of these variables.
ii) Find the equation (with the correct parameters) that will determine the transient
response in this circuit and calculate the values for VC, IC, and VR at 3 and 5 time
constants, respectively.
Fig. 1.b
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Question 1 (continued)
(c) For the circuit in Fig. 1.c, find the impedance and phase angle.
Fig. 1.c
(d) For the circuit in Fig. 1.d:
i) Find the total current (Itot), VR, VL, and VC.
ii) Is this circuit capacitive, inductive, or resistive? As such, what is the phase
relationship between the input voltage and the current? Explain your answer.
iii) Calculate the phase angle and draw the voltage phasor diagram. Describe the phase
relationships between the various voltages (VR, VL, and VC) and the current.
Fig. 1.d
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Question 1 (continued)
(e) For the circuit in Fig.1.e, calculate the current at the following times assuming the
inductor is unexcited at t = 0 (the plot on the right shows the input signal):
i) 10s.
ii) 80s.
Fig. 1.e
(f) Examine the circuit in Fig. 1.f and answer the following questions.
i) Find the reactances XL and XC as well as the total impedance Ztot.
ii) Is this circuit capacitive, inductive, or resistive? Why? As such, what is the phase
relationship between the input voltage and the current? Explain your answer.
iii) Calculate the branch currents (IR, IL, and IC) and the phase angle, and draw the
current phasor diagram.
Fig. 1.f
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Question 1 (continued)
(g) For the circuit in Fig. 1.g, what is the value of the secondary voltage Vsec? Describe
Faraday’s law and explain why (or not) it is relevant in this question. Assume the
transformer is ideal.
Hint: carefully observe the type of input signal.
Fig. 1.g
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CE164-4-SP 6
Question 2
(a) For the series magnetic circuit in Fig. 2.a.i:
i) Find the value of I needed to develop a magnetic flux of 3.0 mWb. Use the curve
in Figure 2.a.ii as necessary.
ii) Using the current you calculated, find the magnetomotive force and the reluctance.
Show the correct units.
Fig. 2.a.i
Fig. 2.a.ii
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Question 2 (continued)
(b) From the hysteresis curves in Fig. 2.b, determine which of the three materials has the
most retentivity. Explain your reasoning, including a brief explanation of what the term
magnetic retentivity means.
Note: H = magnetic field intensity; B = flux density.
Fig.2.b
(c) With regard to standard rectifier diodes:
i) Draw the ‘practical’ and ‘complete’ circuit models, respectively, for a diode in
reverse bias as well as the full (reverse and forward) corresponding characteristic
curves.
ii) Discuss the main differences between these models and when each one of them
should be used.
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Question 2 (continued)
(d) In the CE164 laboratory activities, you built a DC power supply unit (PSU) designed to
deliver 5.5V DC output for an AC input of 240Vrms and 50Hz. The PSU had four main
stages.
i) Draw a diagram including all four stages in the PSU, labelling each stage according
to its main function and showing the approximate voltage wave shape at the output
of each stage.
ii) Suppose that a certain load connected to the PSU requires 15V peak-to-peak to
come out of the rectification stage. What will have to be the peak-to-peak
transformer secondary voltage (Vsec-pp) to deliver this voltage? Also what number
of turns is required in the secondary to obtain the Vsec-pp you calculated? Assume
that we are using a bridge rectifier, and that the primary has 500 turns. Use the
‘practical’ diode model.
iii) Where in the block diagram you drew above would a Zener diode be most useful?
Explain why, including a description of how a Zener diode would perform the
desired function. Use the Zener diode’s V-I characteristic curve in Fig. 2.d and refer
to the relevant labelled points in your explanation.
Fig. 2.d
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Question 2 (continued)
(e) What is the collector current in the circuit in Fig. 2.e if DC = 0.85?
Fig. 2.e
(f) Explain why negative feedback is used in amplification systems with OpAmps. Include
5 reasons in your explanation. Also, what is the main disadvantage of using negative
feedback?
(g) For the circuit in Fig. 2.g, calculate the values for the following variables:
i) Iin.
ii) If.
iii) Vout.
iv) Closed-loop gain.
Fig. 2.g
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EQUATIONS
These are provided 'as is' and as memory aids only. They are presented in no particular
order. Not all equations are needed for the questions above, and the simplest equations (e.g.,
Ohm's law, BJT current relationships, etc.) are not included here.