Question 1. Which of the following devices is suitable for alarm triggering in a security system?
a) Thermister
b) Mositure sensor
c) Light dependent resistor
d) Light emitting diode
Question 2. Which of the following devices is suitable for automatic temperature control in an air-conditioned room?
a) Thermister
b) Light dependent resistor
c) Mositure sensor
d) Light emitting diode
Question 3. Which of the following devices is suitable for automatic control of shutter speed of a digital camera?
a) Thermister
b) Light dependent resistor
c) Mositure sensor
d) Light emitting diode
Question 4. Which of the following devices is NOT a transducer?
a) Thermister
b) Light dependent resistor
c) Mositure sensor
d) Light emitting diode
Question 5. A transducer is normally situated in the control circuit because:
a) There is no way to place. It in the high current circuit
b) It cannot function properly in the high current circuit
c) The control circuit consumes little current to function hence making circuit highly efficient.
d) it makes maintenance easy
Question 6. In a control circuit which either allow the delivery of full power to a load or cuts it off totally, the transistor here is functionally as an electronic switch operates.
a) Either in "cut off" mode or in "saturation" mode
b) Either in "cut off" mode or in "active" mode
c) Either in "liner" mode or in "saturation" mode
d) Either in "saturation" mode or in "breakdown" mode
Question 7. The purpose of placing a diode across the reply in a transistor switch circuit is:
a) to return the energy in the magnetic field of the rely to the circuit during turn-on period so as to protect the transistor from damage.
b) To return the energy in the magnetic field of the relay to the circuit during turn-off period so as to protect the transistor from damage.
c) To help the energy flow in the magnetic field of the reply from the circuit during turn-on period so as to protect the transistor.
d) To block the energy in the magnetic field of the reply to the circuit during turn-on period so as to protect the transistor.
Question 8. The expression v= 20sin(2000t - 30°)v tells us the information of
a) Vrms = 20V, f=2000Hz, phase angle = 30°
b) Vrms = 20V, f=2000Hz, phase angle = -30°
c) Vrms = 20V, f=318Hz, phase angle = -30°
d) Vrms = 20V, f=1000Hz, phase angle = -30°
working: Period 2x(3.142) / 2000 = 0.003141592
frequency = 1/ 0.003141592 = 318Hz
Question 9. The product of two phasors A = 200(/) - 30° and B (/)150° is:
a) A x B = 360 (/) - 4500°
b) A x B = 360 (/) 180°
c) A x B = 360 (/) 120°
d) A x B = 360 (/) -120°
Question 10. The sum of V1 = 15(/) 30°V and V2 = 20 (/) - 45°V is:
a) V1 + V2 = 27.93(/) 13.75°V
b) V1 + V2 = 35(/) 13.75°V
c) V1 + V2 = 27.93(/) - 13.75°V
d) V1 + V2 = 35 (/) - 15°V
Question 11. The polar format V = 20 (/) - 60°V has the corresponding rectangular form:
a) V = (10 + j17.32)V
b) V = (-17.32 + j10)V
c) V = (-10 + j17.32)V
d) V = (10 -j17.32)V
Question 13. The effect of extremely high open-loop voltage gain in op-amp can be reduce by:
a) Selecting an op-amp with desirable open-loop voltage gain value.
b) Selecting appropriate supply voltage to the op-amp circuit
c) introducing a closed loop configuration with a negative feedback to the op-amp
d) Further reducing the signal level as its input terminals.
Question 14. An op-amp may be used in any of the three input mode. which is NOT the one?
a) Single - ended input mode
b) Differential input mode
c) common input mode
d) zero signal input mode
Question 15. which of the following is NOT one of the characteristics of an ideal op-amp?
a) infinite Voltage gain
b) infinite input impedance
c) infinite output impedance
d) infinite bandwidth
Question 16. The two signal input terminals to an op-amp are called:
a) Supply voltage lines Vcc and - Vcc
b) inverting input and non - inverting input
c) Reversing input and non -reversing input
d) Signal input and feedback input
Question 18. An op-amp configured as a voltage follower is used as a buffer in a circuit where by:
a) A matching is required between a low internal resistance of signal source and a low resistive load.
b) A matching is required between a high internal resistance of signal source and a low resistive load.
c) A matching is required between a high internal resistance of signal source and a high resistive load.
d) A matching is required between a low resistance of signal source and a high resistive load.
Question 19. Determine the voltage across resistor R1 in the circuit attached indicate the polarity of the voltage drop.
a) VAB = -8V
b) VAB = 8V
c) VAB = 32V
d) VAB = -32V
Question 20 what is the total resistance across node 'a' and 'b' in the circuit attached?
a) 16k ohm
b) 20k ohm
c) 10k ohm
b) 20k ohm
c) 10k ohm
d) 23.33k ohm
Question 21. what is the voltage drop across resistor Resistor R2 in the circuit attached?
a) 2.5V
b) 7.5V
c) 10 V
d) 3.33V
working:
Total resistance = 5.3K ohm
Voltage across R1 = R1/RT x VT
= 2K ohm / 5.3K ohm x 12V = 4.528V
working:
Total resistance = 5.3K ohm
Voltage across R1 = R1/RT x VT
= 2K ohm / 5.3K ohm x 12V = 4.528V
12 - 4.528V = 7.472
Question 22. What is the current flowing through resistor R3 in the circuit attached?
Question 22. What is the current flowing through resistor R3 in the circuit attached?
a) 1.5 mA
b) 2.25 mA
c) 1mA
d) 0.75mA
working:
Total resistance = 5.3k ohm
Total resistance = 5.3k ohm
I = V/R
= 12V / 5.3K ohm
= 2.26mA
RT/ R3 x IT =
3.33k ohm / 5k ohm x 2.26 mA = 1.5mA
Question 23. Determine the current flowing through resistor R2 in the circuit attached indicate its flow direction.
= 12V / 5.3K ohm
= 2.26mA
RT/ R3 x IT =
3.33k ohm / 5k ohm x 2.26 mA = 1.5mA
Question 23. Determine the current flowing through resistor R2 in the circuit attached indicate its flow direction.
a) 0.9 mA upward
b) 0.9 mA downward
c) 0.6 mA upward
d) 0.6 mA downward
working:
Question 24. Determine the current flowing through resistor R2 in the circuit attached.
Indicate its flow direction.
Indicate its flow direction.
a) 0.9 mA upward
b) 0.9 mA downward
c) 0.6 mA downward
d) 0.6 mA upward
working:
short 6V/ current through R2 is 0.75mA
b) 0.9 mA downward
c) 0.6 mA downward
d) 0.6 mA upward
working:
short 6V/ current through R2 is 0.75mA
short 12V/ current through R2 is 0.15mA
0.75mA - 0.15mA = 0.6 mA
Take Assessment: Quiz 2
Question 1. In a DC serials RC circuit, If R = 10kw , and C = 47 mF (microF), then its time constant is:
a) 0.47s
b) 4.7s
c) 47 ms
d) 470s
working:
t = R.C
= (10 x 10^3) x (47 x 10^-6)
= 0.47s
Question 2. When two capacitors of 22 mF (microF) each are connected in parallel, the effective capacitance now is:
a) 72 mF(microF)
b) 11 mF(microF)
c) 44 mF(microF)
d) 0 mF(microF)
working:
22uF + 22uF = 44uF
Question 3. when two capacitor of 22mF (microF) each are connected in serials, its total effective capacitance now is _______.
a) 22mF (micro farad)
b) 11mF (micro farad)
c) 44mF (micro farad)
d) infinity vaule
working:
22^-1 + 22^-1 = 11uF
Question 4. In an AC capactive circuit, the measured rms voltage across the capacitor is 200V and measured rms current is 1.5mA. Its reactive power is
a) 300mW
b) 300mVAR
c) OVAR
d) 0 W
working:
The reactive power, Q , can be calculated as follows.
Q = Vs(rms) I(rms) sin(/)
= 200V x 1.5 x 10^-3
= 0.3 VAR
= 300mVAR
Question 5. In an AC capacitive circuit, the measured rms voltage across the capapcitor is 200V and measured rms current is 1.5mA. Its real power is:
a) 300 mW
b) 300 mVAR
c) 0 W
d) 0 VAR
Hint: real power is in W
Question 6. In an AC circuit experiment, it is observed that the voltage waveform is lagging the current waveform. It is likely that the circuit is _______ .
a) cannot be determine because its operating frequency is not given
b) capactive
c) inductive
d) purely resistive
Hint: The capacitor voltage lags the capacitor current by 90°
Question 7. A circuit consists of two capacitor C1 and C2 connected together. It is measured that the overall capacitance value is larger than C1, then it can be concluded that:
a) C1 is larger than C2
b) C1 and C2 are connected in parallel
c) C1 and C2 are connect in series
d) C2 is larger than C1
Question 8. When a capacitor is discharging through a circuit, _______
a) It initial current is 0A, and its initial voltage is at its maximum value.
b) Both of its initial current and voltage values are at their maximum values respectively
c) its initial current is at its maximum, and its initial voltage is at 0V
d) Both of its initial current and voltage values are at 0A and 0V respectively
Question 9 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) 325V
b) 230V
c) 103.5V
d) 51.8V
Question 10 In a series RL circuit, the circuit current ______ the applied voltage by _____.
a) leads 90°
b) lag 90°
c) in phase 0°
d) lags , between 0° and 90°
Question 11. The power factor of an ac power circuit has a value of 0.77 lagging mean that;
a) There is at least one reactive component in the circuit, and it is inductive.
b) There is at least one reactive component in the circuit, and it is capactive.
c) Components cannot be determined because no additional information is available.
d) The circuit has a large resistance , so large that the current is lagging the applied voltage.
Question 12. An ac circuit has an impedance Z made up of R = 15W (ohm) and reactance of -jX = j15W (Ohm). Magnitude of Z is therefore:
a) 30W (ohm)
b) 0W (ohm)
c) 21.21W (ohm)
d) 54.8W (ohm)
working:
|z| = square root ((15)^2 + (15)^2)
= 21.21
Question 13. An ac circuit has an impedance Z = 20 + j15W(ohm). It's power factor is:
a) 0.8 leading
b) 0.8 lagging
c) 0.75 leading
d) 0.75 lagging
working:
(inverse tangent) tan-1(15/20) = 36.9°
power factor = cos (/)
= cos 36.9° = 0.79
Question 14. In an ac circuit, the impedance in the rectangular form Z = 25+j20W (Ohm) suggests that it consists of two elements : a resistor and _________.
a) An inductor and its reactance has a phase angle of 90°
b) A capacitor and its reactance has a phase angle of 90°
c) An inductor and its reactance has a phase angle of -90°
d) A capacitor and its reactance has a phase angle of -90°
Question 15. In dc power supply, line regulation refers to:
a) Percentage of output voltage change due to input voltage variation
b) Percentage of inout voltage change due to output voltage variation
c) Percentage of output voltage change due to input current variation
d) Percentage of output voltage change due to output current variation
Hint: Line Regulation = (Vout / Vin ) x 100%
Question 16. A voltage regulator has a 5V output when there is no load. when there is a full load , its output is 4.9V. Its load regulation is:
a) 2.04%
b) 2%
c) 0.1mV
d) 10%
working:
Load Regulation = (( VNL - VFL) / VFL) x 100%
= ((5 - 4.9) / 4.9) x 100%
Question 17. What is the PIV of diode D1 in circuit? Assume that the forward voltage of a diode is 0.7V
a) 0.7V
b) 27.58V
c) 19.3 V
d) 26.88V
Question 18. For the circuit shown here, input ac source has a peak of 30V. If the forward bias voltage of diode is 0.7V, the voltage waveform across resistor R2 varies between;
c) 11.3V and 30V
d) 11.3V and 15V
working:
-0.7 + 12 = 11.3V
Vp(out) = (RL / (R1 + RL)) x Vp(in)
= ( 1000 ohm / (1000 ohm + 1000 ohm)) x 30Vp
= 15V
Question 19. For an ac power circuit with known values of S, P, Q, Z, R, X, Vs, Is and f (phase angle between supply voltage Vs and total circuit current Is), the power factor is incorrectly determined from the expression:
a) Cosine f = Ratio of P to S
b) Cosine f = Ratio of Vs to Is
c) Cosine f = Ratio of R to Z
d) Cosine f = Ratio of (Is^2.R) to (Is.Vs)
Question 20. if an ac circuit has an admittance Y = 0.2 - j0.2s, its reactance is:
a) 2.5w inductive reactance
b) 2.5w , capacitive reactance
c) 5w, inductive reactance
d) 5w, capactive reactance
Question 21. A 20V, 50Hz ac voltage is connected to a circuit of impedance:
Z = 25 < 35° ohm
Determine the S,P,Q delivered.
a) S= 16VA ; P = 13.1 W, Q= 9.18VAR
b) S= 16VA ; P = 9.18 W, Q= 13.1VAR
c) S= 9.18VA ; P = 13.1 W, Q= 16VAR
d) S= 13.1VA ; P = 16 W, Q= 9.18VAR
Working:
ZT = 25<35°ohm I = V / ZT
= 20.5 + j 14.3 I = 20<0° / 25<35
= 0.8 < -35°
S = I^2 x ZT = 0.8^2 x 25 = 16
Question 22. A 30V, 1KHz ac voltage source is connected to a circuit of impedance: Z = 5<-25°K(ohm)
Determine its circuit current (I) , and its power factor (pf)
a) I = 6<25°mA pf = 0.906 leading
b) I = 6<-25°mA pf = 0.906 lagging
c) I = 6<65°mA pf = 0.42 leading
d) I = 6<-65°mA pf = 0.42 lagging
working:
I = V/Z
= 30V < 0 / 5 < -25°K Ohm
= 6 < 25° mA
power factor = cos 25° = 0.906
Question 23 A rectifier produces an output voltage waveform as shown in the file attached , determine the ripple factor iif Vp = 101V , Vdc = 100V
a) 1%
b) 2%
c) 0.57%
d) 1.15%
working =
Vr(p-p) / 2square root (3) x Vdc
= 202 / 2square root(3) x 100v
= 0.58%
Question 24. In the circuit shown here, the value of current I is ________.
Assume Vo = 0.7v when it forward biased.
a) 1.65mA
b) 2mA
c) 3.65mA
d) 4.25 mA
working:
VF = 0.7V
IF = (VBIAS - VF) / R
= ( 8V - 0.7V) / 2000
= 0.00365A
Question 25. The circuit show here is a loaded Zener regulator Vz = 6.3V at 35mA, Izk = 1mA, Zz= 10w and Izm = 75mA. when diode current is at Izm, the minimum current flowing through the 33W resistor is ______.
a) 100 mA
b) 75 mA
c) 40 mA
d) 35 mA
0.75mA - 0.15mA = 0.6 mA
Take Assessment: Quiz 2
Question 1. In a DC serials RC circuit, If R = 10kw , and C = 47 mF (microF), then its time constant is:
a) 0.47s
b) 4.7s
c) 47 ms
d) 470s
working:
t = R.C
= (10 x 10^3) x (47 x 10^-6)
= 0.47s
Question 2. When two capacitors of 22 mF (microF) each are connected in parallel, the effective capacitance now is:
a) 72 mF(microF)
b) 11 mF(microF)
c) 44 mF(microF)
d) 0 mF(microF)
working:
22uF + 22uF = 44uF
Question 3. when two capacitor of 22mF (microF) each are connected in serials, its total effective capacitance now is _______.
a) 22mF (micro farad)
b) 11mF (micro farad)
c) 44mF (micro farad)
d) infinity vaule
working:
22^-1 + 22^-1 = 11uF
Question 4. In an AC capactive circuit, the measured rms voltage across the capacitor is 200V and measured rms current is 1.5mA. Its reactive power is
a) 300mW
b) 300mVAR
c) OVAR
d) 0 W
working:
The reactive power, Q , can be calculated as follows.
Q = Vs(rms) I(rms) sin(/)
= 200V x 1.5 x 10^-3
= 0.3 VAR
= 300mVAR
Question 5. In an AC capacitive circuit, the measured rms voltage across the capapcitor is 200V and measured rms current is 1.5mA. Its real power is:
a) 300 mW
b) 300 mVAR
c) 0 W
d) 0 VAR
Hint: real power is in W
Question 6. In an AC circuit experiment, it is observed that the voltage waveform is lagging the current waveform. It is likely that the circuit is _______ .
a) cannot be determine because its operating frequency is not given
b) capactive
c) inductive
d) purely resistive
Hint: The capacitor voltage lags the capacitor current by 90°
Question 7. A circuit consists of two capacitor C1 and C2 connected together. It is measured that the overall capacitance value is larger than C1, then it can be concluded that:
a) C1 is larger than C2
b) C1 and C2 are connected in parallel
c) C1 and C2 are connect in series
d) C2 is larger than C1
Question 8. When a capacitor is discharging through a circuit, _______
a) It initial current is 0A, and its initial voltage is at its maximum value.
b) Both of its initial current and voltage values are at their maximum values respectively
c) its initial current is at its maximum, and its initial voltage is at 0V
d) Both of its initial current and voltage values are at 0A and 0V respectively
Question 9 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) 325V
b) 230V
c) 103.5V
d) 51.8V
Question 10 In a series RL circuit, the circuit current ______ the applied voltage by _____.
a) leads 90°
b) lag 90°
c) in phase 0°
d) lags , between 0° and 90°
Question 11. The power factor of an ac power circuit has a value of 0.77 lagging mean that;
a) There is at least one reactive component in the circuit, and it is inductive.
b) There is at least one reactive component in the circuit, and it is capactive.
c) Components cannot be determined because no additional information is available.
d) The circuit has a large resistance , so large that the current is lagging the applied voltage.
Question 12. An ac circuit has an impedance Z made up of R = 15W (ohm) and reactance of -jX = j15W (Ohm). Magnitude of Z is therefore:
a) 30W (ohm)
b) 0W (ohm)
c) 21.21W (ohm)
d) 54.8W (ohm)
working:
|z| = square root ((15)^2 + (15)^2)
= 21.21
Question 13. An ac circuit has an impedance Z = 20 + j15W(ohm). It's power factor is:
a) 0.8 leading
b) 0.8 lagging
c) 0.75 leading
d) 0.75 lagging
working:
(inverse tangent) tan-1(15/20) = 36.9°
power factor = cos (/)
= cos 36.9° = 0.79
Question 14. In an ac circuit, the impedance in the rectangular form Z = 25+j20W (Ohm) suggests that it consists of two elements : a resistor and _________.
a) An inductor and its reactance has a phase angle of 90°
b) A capacitor and its reactance has a phase angle of 90°
c) An inductor and its reactance has a phase angle of -90°
d) A capacitor and its reactance has a phase angle of -90°
Question 15. In dc power supply, line regulation refers to:
a) Percentage of output voltage change due to input voltage variation
b) Percentage of inout voltage change due to output voltage variation
c) Percentage of output voltage change due to input current variation
d) Percentage of output voltage change due to output current variation
Hint: Line Regulation = (Vout / Vin ) x 100%
Question 16. A voltage regulator has a 5V output when there is no load. when there is a full load , its output is 4.9V. Its load regulation is:
a) 2.04%
b) 2%
c) 0.1mV
d) 10%
working:
Load Regulation = (( VNL - VFL) / VFL) x 100%
= ((5 - 4.9) / 4.9) x 100%
Question 17. What is the PIV of diode D1 in circuit? Assume that the forward voltage of a diode is 0.7V
a) 0.7V
b) 27.58V
c) 19.3 V
d) 26.88V
Question 18. For the circuit shown here, input ac source has a peak of 30V. If the forward bias voltage of diode is 0.7V, the voltage waveform across resistor R2 varies between;
a) 0V and 30V
b) 0V and 15Vc) 11.3V and 30V
d) 11.3V and 15V
working:
-0.7 + 12 = 11.3V
Vp(out) = (RL / (R1 + RL)) x Vp(in)
= ( 1000 ohm / (1000 ohm + 1000 ohm)) x 30Vp
= 15V
a) Cosine f = Ratio of P to S
b) Cosine f = Ratio of Vs to Is
c) Cosine f = Ratio of R to Z
d) Cosine f = Ratio of (Is^2.R) to (Is.Vs)
Question 20. if an ac circuit has an admittance Y = 0.2 - j0.2s, its reactance is:
a) 2.5w inductive reactance
b) 2.5w , capacitive reactance
c) 5w, inductive reactance
d) 5w, capactive reactance
Question 21. A 20V, 50Hz ac voltage is connected to a circuit of impedance:
Z = 25 < 35° ohm
Determine the S,P,Q delivered.
a) S= 16VA ; P = 13.1 W, Q= 9.18VAR
b) S= 16VA ; P = 9.18 W, Q= 13.1VAR
c) S= 9.18VA ; P = 13.1 W, Q= 16VAR
d) S= 13.1VA ; P = 16 W, Q= 9.18VAR
Working:
ZT = 25<35°ohm I = V / ZT
= 20.5 + j 14.3 I = 20<0° / 25<35
= 0.8 < -35°
P = I^2 x R = 0.8^2 x 20.5 = 13.12
Q = I^2 x XL = 0.8^2 x 14.3 = 9.152S = I^2 x ZT = 0.8^2 x 25 = 16
Question 22. A 30V, 1KHz ac voltage source is connected to a circuit of impedance: Z = 5<-25°K(ohm)
Determine its circuit current (I) , and its power factor (pf)
a) I = 6<25°mA pf = 0.906 leading
b) I = 6<-25°mA pf = 0.906 lagging
c) I = 6<65°mA pf = 0.42 leading
d) I = 6<-65°mA pf = 0.42 lagging
working:
I = V/Z
= 30V < 0 / 5 < -25°K Ohm
= 6 < 25° mA
power factor = cos 25° = 0.906
Question 23 A rectifier produces an output voltage waveform as shown in the file attached , determine the ripple factor iif Vp = 101V , Vdc = 100V
a) 1%
b) 2%
c) 0.57%
d) 1.15%
working =
Vr(p-p) / 2square root (3) x Vdc
= 202 / 2square root(3) x 100v
= 0.58%
Question 24. In the circuit shown here, the value of current I is ________.
Assume Vo = 0.7v when it forward biased.
a) 1.65mA
b) 2mA
c) 3.65mA
d) 4.25 mA
working:
VF = 0.7V
IF = (VBIAS - VF) / R
= ( 8V - 0.7V) / 2000
= 0.00365A
Question 25. The circuit show here is a loaded Zener regulator Vz = 6.3V at 35mA, Izk = 1mA, Zz= 10w and Izm = 75mA. when diode current is at Izm, the minimum current flowing through the 33W resistor is ______.
a) 100 mA
b) 75 mA
c) 40 mA
d) 35 mA
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