You must have done your tutorial problems and Quiz 1 before you attempt the questions below.
A1. Which one of the following currents is the smallest?
(a) 10,000 nA
(b) 100 μA
(c) 0.1 mA
(d) 1 x 10^-4 A
A2. The sum of 25 mA and 8000 μA is:
(a) 25.008 mA
(b) 8025 μA
(c) 33 mA
(d) 33 μA
A3. Express 0.000000001290 A in metric prefix notation.
(a) 129 nA
(b) 1.29 pA
(c) 129 pA
(d) 1.29 nA
A4. A certain material has atoms which have 7 valence electrons. This material is likely to
be a or an __________.
(a) conductor
(b) insulator
(c) ionizer
(d) semiconductor
A5. A certain element is made up of atoms that have 5 valence electrons. This element is
likely to be an electrical ___________.
(a) conductor
(b) semiconductor
(c) insulator
(d) ionizer
A6. A length of wire has a resistance of 10m ohm. If its length is increased 4 times and radius
is halved, find the new resistance of the wire.
(a) 10 m ohm.
(b) 20 m ohm.
(c) 80 m ohm.
(d) 0.16 ohm
A7. A conductor of length 2.5 m, has a cross-sectional area of 0.3 x 10-6 m(square), and a
resistance of 0.06 Ohms. What is the resistance of another conductor of the same
material but having a length of 25 m, and has a cross-sectional area of 0.1 x 10^-6 m(square) ?
(a) 0.2 ohm
(b) 0.6 ohm
(c) 1.8 ohm
(d) 2.5 ohm
working:
0.06 = 2.5m.P/ 0.3 x 10^-6
0.06(0.3x10^-6) = 2.5mP
0.06(0.3x10^-6)/2.5 = P
0.000000007 = P
P25 (0.000000007) / 0.1 x 10^-6
= 1.8 ohm
A8. Given the table in Figure A8, a resistor with a 4-band colour code: orange, orange, red, gold will have a resistance range between
(a) 315.4 ohm to 348.6 ohm
(b) 313.5 ohm to 346.5 ohm
(c) 2.97k ohm to 3.63k ohm
(d) 3.14k ohm to 3.47k ohm
A9. Which one of the following resistors dissipates the most power?
(a) R1 : 10 k ohm with 30V across it
(b) R2 : 4 V across it and 20 mA flowing through it 1.8 ohm
(c) R3 : 10 k ohm and 2 mA flowing through it
(d) R4 : power dissipated is 75 mW
working:
a) 30^2 / 10 K ohm = 0.09w
b) (20mA)^2 x 1.8 ohm = 0.036w
c) 2mA x 10K ohm = 0.04 w
d) 75mw = 0.075w
A10. An air-conditioner, rated at 1500W, is turned on for 8 hours everyday. Assuming that it runs at its rated power all the time, calculate the amount of energy it consumes in a week.
(a) 84 kJ
(b) 5.04 MJ
(c) 12 kWh t
(d) 84 kWh
working:
Energy = power x time
= 1500w x 8 hours
= 12000 = 12kwh
12kwh x 7 = 84 kwh
A11. With reference to the circuit in Figure A11, which one of the following expressions is correct?
(a) Vs = - I x (R1 + R2)
(b) V1 + V2 = 0
(c) Vs + V1 + V2 = 0
(d) Vs = V1 + V2
A12. The voltage V1 in voltage divider shown in figure A12 is
(a) 1V
(b) 2V
(c) 10V
(d) cannot be found because R is unknown
Working :
current = 12 / 6 ohm = 2A
Vr = I x 2A = 2V
current = 12 / 6 ohm = 2A
Vr = I x 2A = 2V
A13. Two resistors are connected in parallel. Their total resistance is 1.2 k ohm . If one resistor is 2 k ohm , what is the value of the other resistor?
(a) 0.5 k ohm
(b) 0.75 k ohm
(c) 3 k ohm
(d) 3.25 k ohm
working:
1.2k ohm ^-1 - 2k ohm ^-1 = 0.333333333^-1 = 3K ohm
A14. 2 resistors RA and RB are connected in parallel. RA has its length doubled, while RB has its cross-sectional area halved. The total resistance of the parallel connection has
(a) remained the same
(b) doubled
(c) quadrupled
(d) halved
A15. The current I1 and I2 in Figure A15 is
(a) 22mA and 13mA respectively
(b) -22mA and 13mA respectively
(c) -22mA and 35mA respectively
(d) 22mA and 35mA respectively
A15 The current I1 and I2 in Figure A15 is
(a) 22mA and 13mA respectively
(b) -22mA and 13mA respectively
(c) -22mA and 35mA respectively
(d) 22mA and 35mA respectively
B1. (a) 49J of energy is required to move 4.375 x 10^19 electrons through a resistor in 140 seconds. Given that 6.25x10^18 electrons produce 1 C of charge, calculate the
following
i) the voltage across the resistor
ii) the current across the resistor
iii) the resistance of the resistor
iv) the minimum standard power rating of the resistor
working:
C = number of electrons / 6.25 x 10^18
= 4.375 x 10^19 / 6.25 x 10^18
= 7C
i) V = 49J / 7C
= 7V
ii) I = 7C/140s = 0.05A = 50mA
iii) R = 7V / 50mA = 140 ohm
iv) P = 49J / 140s = 0.35w
minimum standard power rating 0.5w
(b) The resistance of a wire with diameter d0 is R0. Given that the resistivity and length of the wire remains unchanged, find the new wire diameter if its resistance is increased to 2R0. Leave your answer in terms of d0.
Ans: 0.707
B2. The circuit shown in Figure B2 consists of 2 fixed resistors connected in series with a 500 ohm variable resistor. Find the minimum and maximum value of voltage Vo. Calculate also the correct power ratings of each resistor to use.
Vo max = Vs x Rmax / RT Vo min = Vs x Rmin / RT
= 60V x 1.5 / 3K = 60V x 1 / 3K
= 30V = 20V
I = V/R
= 60V / 3K ohm
= 20mA
Pr1 = 20mA^2 x 1.5k ohm = 0.6 w (power rating = 1w)
Pr2 = 20mA^2 x 500 ohm = 0.2 w (power rating = 0.25w)
Pr3 = 20mA^2 x 1K ohm = 0.4 w (power rating = 0.5 w)
B3. Find the value of I, VAB and VAC in the circuit shown in Figure B3.
Total Voltage = 12v + 3v - 9v = 6v
Total Resistance = 1k ohm + 2k ohm + 500 ohm = 3.5k ohm
current = 6v / 3.5k ohm = 1.71 mA
VAB = 500ohm x 1.71 mA = 0.855V
Voltage across 1k ohm = 1K ohm x 1.71mA = 1.71V
Volatge across 2K ohm = 2K ohm x 1.71 mA = 3.42V
VAC = 12V - 1.7V - 3.42V = 6.87V
Answers to the Selected Past Year Paper for Revision: Questions on Chapters 1 – 6
A1: (a) 10,000 nA
A2: (c) 33 mA
A3: (d) 1.29 nA
A4: (b) insulator
A5: (c) insulator
A6: (d) 0.16 Ω
A7: (c) 1.8 Ω
A8: (d) 3.14kΩ to 3.47kΩ
A9: (a) R1: 10 kΩ with 30V across it
A10: (d) 84 kWh
A11: (d) Vs = V1 + V2
A12: (b) 2V
A13: (c) 3 kΩ
A14: (c) quadrupled
A15: (b) -22mA and 13mA respectively
B1: (a) (i) 7V, (ii) 50mA, (iii) 140Ω, (iv) half watt; (b) 0.707do
B2: Vo(max) is 30V, Vo(min) is 20V, 1W, 0.25W, 0.5W
B3: 1.71 mA, 0.855V, 6.87V
2010/2011 SEMESTER ONE MID-SEMESTER TEST SAS Code TST1
Diploma in Aerospace Electronics (DASE)
Diploma in Clean Energy (DCEG)
Diploma in Computer Engineering (DCPE)
Diploma in Electrical & Electronic Engineering (DEEE)
Common Engineering Programme (DCEP)
1st Year FT, 1st Year EO
A1 The number "62300" can be expressed in scientific notation as _________.
(a) 0.623 x 10^5
(b) 6.23 x 10^4
(c) 62.3 x 10^3
(d) 623 x 10^2
A2 The number "0.000523" can be expressed in engineering notation as __________.
(a) 523 x 10^-6
(b) 5.23 x 10^-5
(c) 5.23 x 10^-4
(d) 5230 x 10^-7
A3. The value "5.2 x 10^-2 V" can be expressed using metric prefix as __________.
(a) 52 mV
(b) 52 MV
(c) 52 kV
(d) 0.052 V
A4. An element has an atomic number of 29. Which of the following is NOT correct?
(a) It has 29 orbiting electrons
(b) It has 1 electron in its outermost shell
(c) It has 1 valence electron
(d) It will make a good insulator
A5. Resistance of a material depends on the following factors:
(a) Resistivity, Length, cross-section area, temperature
(b) Current, voltage, resistivity, length
(c) Current, voltage, length, cross-section
(d) Resistivity , current, voltage, temperature
A6. When the voltage applied across a resistor is double, and its resistance value is halved, the current flowing through it will be:
(a) Doubled
(b) Halved
(c) No change
(d) Quadrupled
A7. Three resistors are connected across a common voltage source as shown in Figure A7. Which resistor requires the highest power rating?
(a) R3
(b) R2
(c) R1
(d) All resistors require same power rating
A8. The colour bands of a resistor are given as Red, Red, Red, Gold. Its resistance lies between (Colour code for Red: 2 or x 10^2 , Gold: +5 -5%):
(a) 1980 ohm and 2420 ohm
(b) 198 ohm and 242 ohm
(c) 2090 ohm and 2310 ohm
(d) 209 ohm and 231 ohm
Hint : 2200 +5% 2200 -5%
A9. For the circuit shown in Figure A9, apply KCL to determine the current Ix.
(a) 0A
(b) 2A
(c) 4A
(d) 6A
A10. For the circuit shown in Figure A10, apply KVL to find the voltage across R2.
(a) 2V
(b) 8V
(c) 10V
(d) 20 V
SECTION B
B1 (a) Perform the following operation and express the result in engineering notation
Ans: 50.979w
B2.
(a) A material of a circular cylindrical shape of diameter 2mm and length 0.5 cm long has a resistivity of 5.6 x 10^-8 Ohm meter at 20°C . Determine its resistance across its two ends at 20°C.
Ans: 0.8912 x 10^-4 Ohm
(b) Determine the voltage required across the resistor if 900 J of energy is required to move 35 C of charge through it. How many electrons are required to produce that amount of charge?
Ans: 2.1875 x 10^20
(c) Name four appliances that use resistance to perform a function.
Ans: Kettle, light-bulb, dryer, iron, oven
Answer: (a) 2ma
b) 9.4v , 2.4v , 3.6v , 6.6v
c) 22v, 12.6v, 10.2v , 6.6v
d) 44 mw
B4. A number of resistors of same resistance value are connected in parallel. Each resistor has a power rating of 1/2-W. The effective resistance of the circuit equals to 1k ohm. When the circuit is connected to a voltage source, its total current is 50 mA. If the resistors are dissipating half of their rated power level, determine:
(a) The voltage across each parallel branch.
(b) The current in each branch.
(c) The number of bramches; and hence the number of resistors in each branch.
(d) The value of each resistor.
Ans: (a) 50mA x 1K ohm = 50V
b) PR = 1/4w (* If the resistors are dissipating half of their rated power level)
1/4 = I x Vs
1/4 = I x 50
I = 5mA (each resistor keep 5mA)
B5. The circuit shown in Figure B5 consists of a voltage source Vs and two resistors R1 and R2. If total current IT = 200mA , Total power delivered to the circuit is PT = 2W, and power dissipated in R1 is P1 = 0.75 W, determine:
(a) Voltage Vs;
(b) Power P2 dissipated in R2;
(c) Current IR1 and IR2
(d) Resistance values R1 and R2
Answer: (a) 10V
(b) 1.25W
(c) 75mA , 125mA
(d) 133.3 Ohm , 80 Ohm
Quiz 2 Chapter 9, through 14 , to Chapter 18, Chapter 20 and 212010/2011 SEMESTER ONE MID-SEMESTER TEST SAS Code TST1
Diploma in Aerospace Electronics (DASE)
Diploma in Clean Energy (DCEG)
Diploma in Computer Engineering (DCPE)
Diploma in Electrical & Electronic Engineering (DEEE)
Common Engineering Programme (DCEP)
1st Year FT, 1st Year EO
A1 The number "62300" can be expressed in scientific notation as _________.
(a) 0.623 x 10^5
(b) 6.23 x 10^4
(c) 62.3 x 10^3
(d) 623 x 10^2
A2 The number "0.000523" can be expressed in engineering notation as __________.
(a) 523 x 10^-6
(b) 5.23 x 10^-5
(c) 5.23 x 10^-4
(d) 5230 x 10^-7
A3. The value "5.2 x 10^-2 V" can be expressed using metric prefix as __________.
(a) 52 mV
(b) 52 MV
(c) 52 kV
(d) 0.052 V
A4. An element has an atomic number of 29. Which of the following is NOT correct?
(a) It has 29 orbiting electrons
(b) It has 1 electron in its outermost shell
(c) It has 1 valence electron
(d) It will make a good insulator
A5. Resistance of a material depends on the following factors:
(a) Resistivity, Length, cross-section area, temperature
(b) Current, voltage, resistivity, length
(c) Current, voltage, length, cross-section
(d) Resistivity , current, voltage, temperature
A6. When the voltage applied across a resistor is double, and its resistance value is halved, the current flowing through it will be:
(a) Doubled
(b) Halved
(c) No change
(d) Quadrupled
A7. Three resistors are connected across a common voltage source as shown in Figure A7. Which resistor requires the highest power rating?
(a) R3
(b) R2
(c) R1
(d) All resistors require same power rating
A8. The colour bands of a resistor are given as Red, Red, Red, Gold. Its resistance lies between (Colour code for Red: 2 or x 10^2 , Gold: +5 -5%):
(a) 1980 ohm and 2420 ohm
(b) 198 ohm and 242 ohm
(c) 2090 ohm and 2310 ohm
(d) 209 ohm and 231 ohm
Hint : 2200 +5% 2200 -5%
A9. For the circuit shown in Figure A9, apply KCL to determine the current Ix.
(a) 0A
(b) 2A
(c) 4A
(d) 6A
A10. For the circuit shown in Figure A10, apply KVL to find the voltage across R2.
(a) 2V
(b) 8V
(c) 10V
(d) 20 V
SECTION B
B1 (a) Perform the following operation and express the result in engineering notation
Ans: 0.15
(b) A DC circuit consists of two resistors ,and heater and a light bulb. The total power consumed is given in summing expression below. Perform the operation and express the result using metric prefix.
Ans: 50.979w
B2.
(a) A material of a circular cylindrical shape of diameter 2mm and length 0.5 cm long has a resistivity of 5.6 x 10^-8 Ohm meter at 20°C . Determine its resistance across its two ends at 20°C.
Ans: 0.8912 x 10^-4 Ohm
(b) Determine the voltage required across the resistor if 900 J of energy is required to move 35 C of charge through it. How many electrons are required to produce that amount of charge?
Ans: 2.1875 x 10^20
(c) Name four appliances that use resistance to perform a function.
Ans: Kettle, light-bulb, dryer, iron, oven
B3. For the circuit shown in Figure B3, determine:
(a) The current I of the circuit.
(b) The voltage VR1, VR2, VR3 and VR4.
(c) The voltage VA, VB, VC and VD
(b) The voltage VR1, VR2, VR3 and VR4.
(c) The voltage VA, VB, VC and VD
(d) The total power dissipated in the circuit.
Answer: (a) 2ma
b) 9.4v , 2.4v , 3.6v , 6.6v
c) 22v, 12.6v, 10.2v , 6.6v
d) 44 mw
B4. A number of resistors of same resistance value are connected in parallel. Each resistor has a power rating of 1/2-W. The effective resistance of the circuit equals to 1k ohm. When the circuit is connected to a voltage source, its total current is 50 mA. If the resistors are dissipating half of their rated power level, determine:
(a) The voltage across each parallel branch.
(b) The current in each branch.
(c) The number of bramches; and hence the number of resistors in each branch.
(d) The value of each resistor.
Ans: (a) 50mA x 1K ohm = 50V
b) PR = 1/4w (* If the resistors are dissipating half of their rated power level)
1/4 = I x Vs
1/4 = I x 50
I = 5mA (each resistor keep 5mA)
(a) Voltage Vs;
(b) Power P2 dissipated in R2;
(c) Current IR1 and IR2
(d) Resistance values R1 and R2
Answer: (a) 10V
(b) 1.25W
(c) 75mA , 125mA
(d) 133.3 Ohm , 80 Ohm
Question 1
Transformer operation is based on the principle of _________.
a) Mutual inductance
b) Self inductance
c) Self reactance of coil
d) Mutual reactances of coils
Question 2
A transformer has the following specifications : Vpri = 220v , Vsec = 110V, and its power rating Prating = 2.2 KVA. It's maximum values for Ipri = _____A and Isec= _____A without damaging the transformer
a) 20A, 20A
b) 20A, 10A
c) 10A, 20A
d) 10A, 10A
working: VpIp = VsIs = transformer rating
220v x Ip = 2.2KVA
Ip = 2.2KVA/220V = 10A
110V x Is = 2.2KVA
Is = 2.2 KVA/110V = 20A
Question 3
Transformer cannot be used to : __________
a) step up ac voltage
b) step down ac voltage
c) Couple two ac circuit with different reference grounds
d) Convert ac to dc waveform
Question 4
Which of the following statment is NOT correct?
a) The turns ratio (Nsec : Npri) of a step-down transformer is greater than 1.
b) The Transformer windings are magnetically coupled.
c) in a transformer, the output power is approximately equal to the input power.
d) The transformer primary and secondary circuit are electrically isolated.
* The turns ration of a step-down transformer is less than 1 while step up transformer is greater than 1
Question 5.
Refer to the ac circuit here. if turn ratio n = 0.1, the primary voltage Vpri is _____ and secondary voltage Vsec is _____.
a) 230V, 23V
b) 23V, 230Vc) 325V, 32.5V
d) 32.5V , 325V
working: n = Vs/Vp
0.1 = Vs/230
Vs = 23V
Question 6
a) 0.09A
b) 0.13A
c) 2.3Ad) 3.25A
working:
1) n = Vsec/Vpri
5 = Vsec/230
Vsec = 1150V
2) I = V/R
I = 1150/500ohm= 2.3A
Question 7
Refer to the two coil in Circuit . The coefficient of coupling K=0.3. The mutual inductance is ________.
a) 15mH
b) 7.07 mH
c) 2.12mHd) 15 mH
working:
Lm = k square root(L1.L2)
Lm = 0.3 square root (10mH x 5mH)
= 0.00212132
Question 8
Refer to the circuit here, the total inductance is ________.
a) 6H
b) 0.5mHc) 1.8 mH
d) 6 mH
working:
Lt = L1 + L2 + ... + Ln
= 1mH + 2mH + 3 mH
= 6mH
Question 9
a) 1.833mH
b) 0.546mH
c) 3mHd) 6mH
working:
1/LT = (1/L1 + 1/L2 + ... 1/Ln)
= 1mH^-1 + 2mH^-1 + 3mH^-1
= 1.833333333^-1
= 0.546mH
Question 10
The ac voltage and current in a circuit are
v(t) = 10sin(wt + 50°)v i(t) = 20sin(wt - 30°)v
which statement is ture?
a) i(t) lags v(t) by 20°
b) i(t) lags v(t) by 30°
c) v(t) leads i(t) by 50°
d) v(t) leads i(t) by 80°
Question 11
The self inductance of a coil is 10 mH. If the number of turns of a the coil is double and its length halved, the final inductance of the coil should be _______.
a) 20mH
b) 40 mH
c) 50 mH
d) 80 mH
Question 12
The ac voltage accross a 100ohm resistor in a circuit is given by : V = 28.28 sin(wt) V. The power dissipated in the resistor is ________.
a) 0.2w
b) 4w
c) 8w
d) 16w
working:
rms = 28.28 x 0.707 = 19.99396V
P = V^2 / R
= 19.99396^2 / 100ohm
= 3.997584365w
= 4w
Question 13
For the magnetic circuit shown here, if a current of 2A flowing through a coil of 500 turns , find its magneto motive force.
a) 100 At
b) 1000 At
c) 250 At
d) 2A
working:
magnetomotive force = N(number of turns) x I (current)
= 500 x 2
= 1000
Question 14
For the magnetic Circuit shown here, if the mmf is 100At, and the flax path is 0.5m long. determine the magnetizing force of the core material
a) 50 At-m
b) 100 At
c) 200 At/m
d) 200At-m
working:
(H) = fm/length of material L
= 100At / 0.5 m
= 200At / m
Question 15.
Refer to the magnetic circuit here. A magnetomotive force of 10At establishes a magnetic flux in the core. If the flux density is 27, cross-section area of flux path is 20cm(square) , what is the reluctance of the magnetic circuit?
a) 2500 At/wb
b) 0.8 At/wb
c) 1.25 At/wb
d) 4000 At/wb
Working:
Flux density B = flux (weber) / area perpendicular to flux
2T = flux (weber) / 20 cm (square)
= 0.004wb
Flux (weber) = magnetomotive Force / Reluctance
R = 10At / 0.004 wb
= 2500At/wb
Question 16
The reluctance of the core material of a magnetic circuit depends upon a few factors. which one of the following is NOT a factor?
a) permeability of the material
b) length of the material
c) cross-sectional area of the material
d) weight of the material
Question 17
when two capacitors of 22uF (micro F) each are connected in parallel, the effective capacitance now is:
a) 44uF (micro F)
b) 22uF (micro F)
c) 11uF (micro F)
d) 4uF (micro F)
working:
Ct = C1 + C2 + C3
= 22uF + 22uF
= 44uF
Question 18
Which of the following device operates in the reverse bias condition?
a) PN Junction Diode
b) Light Emitting Diode
c) Photodiode
d) infra Red LED
Question 19
Once a transistor reaches its saturation mode, further increase in base current will ________.
a) not cause further change in collector current
b) cause further increase in collector current
c) cause decrease in collector current
d) cause transistor to switch off completely
Question 20
A circuit consists of two capacitor (C1 and C2) connected together. It is measured that the overall capacitance vaule is lager than C1, then it can be concluded that:
a) C2 is larger than C1
b) C1 is larger than C2
c) C1 and C2 are connected in parallel
d) C1 and C2 are connected in serial
Question 21
In a material, a free electron is one that:
a) has potential energy and is free to move away from the valence band it is in.
b) is not bound to any atom, but free to drift about
c) Enters the valence band from other energy bands within an atom without problem
d) Exits only in conductor material
Question 22
Refer to the transistor circuit here, the base current Ib is kept constant and VBE is forward biased. The entire operating range is within active region of the transistor . which
a) By varying Vcc, Collector IC is constant, VCE is constant throughout.
b) By varying Vcc, Collector IC is constant, VRC is constant but VCE is changing.
c) By varying Vcc, Collector IC is changing, VCE is constant throughout.
d) By varying Vcc, Collector IC is changing, but VCE is constant throughout.
Question 23
Given the forward voltage drop of a LED is 2V. The current flowing in the circuit shown in the diagram is : ________.
a) 14 mA
b) 12 mA
c) 10 mA
d) 0 mA
Question 24
When an ac source of 230V is applied to a heating element, a power of 100 Watts of heat is produced. If the heating element is to be connected to a dc source to produce the same power, what should be the dc voltage source?
a) 325 V
b) 230 V
c) 103.5 V
d) 51.77V
Question 25
To design and construct a capacitor of large capacitance value, given the dielectric material, it is desirable to have:
a) Large surface area of the plates , and small distance between them.
b) small surface area of the plates , and small distance between them.
c) Large surface area of the plates , and large distance between them.
d) small surface area of the plates , and large distance between them.
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