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Homework answers / question archive / ELEC S201F Basic Electronics There are TWO sections in this paper
ELEC S201F Basic Electronics
There are TWO sections in this paper. You should answer altogether NINE (9) questions in this paper.
You should attempt ALL SIX (6) questions in Section A (50 marks). Answer ALL THREE (3) questions in Sections B (50 marks).
SECTION A:
This section carries 50% of the total marks and you should attempt ALL SIX questions.
Question 1 (6 marks)
Consider the circuit in Figure Q1, a load resistor RL is connected to a d.c. voltage source VS with an internal resistance RS.
When RL = 4 k:, the load voltage VL = 15V.
When RL = 2 k:, the load voltage is dropped to VL = (12 + 0.2 × X8) V. e.g. if X8 = 4, VL = 12 + 0.2 × 4 = 12.8 V.
Using voltage divider to find the open-circuit voltage VS and the internal resistance RS of the source as shown in Figure Q1.
(6 marks)
+ |
V |
L |
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Question 2 (10 marks)
For the circuit shown in Figure Q2, a resistor R, a capacitor C = 5 × 10-9 F and an inductor L = 0.1 H.
X7 k: if your X7 z 0 R ®¯10 k: if your X7 0
e.g. if X7 = 0, R = 10 k:.
The input voltage
Vin(t) = 12 cos(2 × 104 t + 30q) V.
(a) Redraw the circuit in Figure Q2 using phasors.
(2 marks) (b) Find the equivalent input impedance of the circuit.
(4 marks) (a) Find the output voltage Vout(t).
(4 marks)
Question 3 (8 marks)
a = X5 and b = X6
e.g. if X5 = 3, X6 = 5, your 3-digit number is 13510
(i) Convert your 3-digit number into an octal number.
(2 marks)
(ii) Find the 2’s complement of your 3-digit number
(2 marks)
X A?CB?C?D A?B?C
Using only INVERTERs, AND-gates and OR-gates, draw a logic diagram of a circuit that generates X. Clearly label the output of each gate with the variable or term that it generates.
(4 marks)
Question 4 (6 marks)
Consider the circuit shown in Figure Q4(a). The transformer is assumed to have no losses with a turn ratio of N:1 and the diode is ideal.
X5u5 if your X5 z 0 where N ®¯ 50 if your X5 0
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. |
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X |
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3 |
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1 |
5 |
The input Vin (t) is a square wave with an amplitude of 10 V and a frequency of 10 Hz, as shown in Figure Q4(b).
(a) Sketch the waveform of the voltage Va (t) at the output of the transformer.
(3 marks) (b) Sketch the waveform of the voltage Vout (t) after passing through the diode.
(3 marks)
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g |
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Question 5 (15 marks)
The switch in the circuit in Figure Q5 has been closed (in position A) for a long time. The switch opens at t = 0 (The switch changes from position A to position B).
Given: VS = 5V, R1 = 2 ?, R2 = 4 ?, R3 = 4 ? and L = 2 H.
F |
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(a) Redraw the circuit in Figure Q5 for the cases: t < 0 and t t 0.
(2 marks) (b) Find the current iL(t) for t < 0.
(4 marks) (c) Find the current iL(t) for t t 0.
(9 marks)
Question 6 (5 marks)
Consider the circuit in Figure Q6, V1 = 6V, V2 = 3V, resistors R1 = 4 k: and
10X8 k: if your X8 z 0 R2 ®¯ 20 k: if your X8 0
e.g. if X8 = 4, R2 = 10 + 4 = 14 k:
Assuming an ideal op-amp, find the output voltage Vout.
Hint: you should use the two Golden rules for the ideal op-amp.
(5 marks)
End of Section A
SECTION B:
This section carries 50% of the total marks and you should attempt ALL THREE (3) questions.
Question 7 (20 marks)
Consider the circuit in Figure Q7. You are going to find the Thevenin equivalent circuit between terminals A and B.
Given an ideal current source IS2 = 2 mA, resistors R1 = 3 k?, R2 = 6 k?, R3 = 4 k?, R4 = 2 k? and an ideal voltage source VS1, where
?7 V if your ?7 0
??110 V if your ?7 0
e.g. if X7 = 0, VS1 = 10V.
(11 marks)
(3 marks)
(6 marks)
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2 |
3 |
Question 8 (20 marks)
Figure Q8(a) shows an arrangement of 9 lamps. Of the many patterns that could be formed, a system only uses the 10 patterns shown in Figure Q8(b) where a filled circle indicates a lamp to be on; a lamp can only be on or off. Table Q8 shows a partially completed table describing the states of the lamp for the input codes (UVWX) used to generate the output patterns in Figure Q8(b) (the decimal equivalent of each code is marked against each pattern). A 0 in the output columns means that the lamp is off, a 1 means that the lamp is on, and an x represents a don't care state.
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Outputs to Lamps (ON = 1) |
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(4 marks)
(2 marks) (c) A partially simplified Boolean expression for lamp g is,
g U?V?W U?W?X U?W ?X
Using only NAND gates, draw a circuit diagram that will produce g from the inputs U, V, W, X.
(3 marks)
(6 marks)
(5 marks)
Question 9 (10 marks)
Consider the circuit in Figure Q9.
Given a sinusoidal voltage source Vin, C1 = 3 PF, C2 = 3 nF, R1 = 250 ? and R2 = 1 k?, where
X6 V if your X6 0 Amplitude of ???10 V if your X6 0 e.g. if X6 = 5, amplitude of Vin = 5V.
Use OrCAD to build the circuit in Figure Q9. You must submit the schematic of your circuit in pdf format. Use OrCAD to simulate the frequency response of your circuit over the range of 1 Hz to 10 MHz, with 100 points per decade.
Vout
Vin
(6 marks)
Vout
Vin
(2 marks) (c) Find the 3-dB frequencies f3dB of this circuit (i.e. the frequencies at which 3 dB below your maximum value in (b)).
(2 marks)
You must submit both the schematic and plot of your simulation results in pdf format.
END OF FINAL PROJECT
Appendix
KCL: |
¦Iin ¦Iout |
KVL: |
¦Vi 0 in a loop i |
v = iR, |
i(t) C dv(t) , v(t) L di(t) dt dt |
Impedance: |
ZC 1 and ZL jZL , where Z = 2Sf jZC |
Power: |
P = V I |
Impedance in series: Z = Z1 + Z2
Impedance in parallel: 1 1 1
Transformer: e2 N2 e1 N1
For the 1st order ODE: Wdx(t) x(t) A
the general solution is: x(t) K1 exp(W t ) K2 , where K1 and K2 are constants.
Please download the answer file using this link
https://drive.google.com/file/d/1R5QIv5RYDqeZbZBB9Bgh3-f6yCwdyBZq/view?usp=sharing