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HAL electronics and electrical computer engg questions and answers, Semi conductors, Transformers,digital electronics objective type multiple choice questions and answers

1. ASK, PSK, FSK, and QAM are examples of ________ conversion.

A) digital-to-digital

B) digital-to-analog-Answer

C) analog-to-analog

D) analog-to-digital



2. AM and FM are examples of ________ conversion.

A) digital-to-digital

B) digital-to-analog

C) analog-to-analog-Answer

D) analog-to-digital



3. In QAM, both ________ of a carrier frequency are varied.

A) frequency and amplitude

B) phase and frequency

C) amplitude and phase-Answer

D) none of the above



4. If the baud rate is 400 for a QPSK signal, the bit rate is ________ bps.

A) 100

B) 400

C) 800-Answer

D) 1600



5. If the bit rate for an ASK signal is 1200 bps, the baud rate is ________.

A) 300

B) 400

C) 600

D) 1200-Answer



6. If the bit rate for an FSK signal is 1200 bps, the baud rate is ________.

A) 300

B) 400

C) 600

D) 1200-Answer



7. If the bit rate for a 16-QAM signal is 4000 bps, what is the baud rate?

A) 300

B) 400

C) 1000-Answer

D) 1200



8. If the baud rate for a 64-QAM signal is 2000, what is the bit rate?

A) 300

B) 400

C) 1000

D) 12000-Answer



9. Given an AM radio signal with a bandwidth of 10 KHz and the highest-frequency component at 705 KHz, what is the frequency of the carrier signal?

A) 700 KHz-Answer

B) 705 KHz

C) 710 KHz

D) Cannot be determined from given information



10. _______ conversion is the process of changing one of the characteristics of an analog signal based on the information in the digital data.

A) Digital-to-analog-Answer

B) Analog-to-analog

C) Analog-to-digital

D) Digital-to-digital



11. Which of the following is not a digital-to-analog conversion?

A) ASK

B) PSK

C) FSK

D) AM-Answer



12. In ________, the amplitude of the carrier signal is varied to create signal elements. Both frequency and phase remain constant.

A) ASK-Answer

B) PSK

C) FSK

D) QAM



13. In _________, the frequency of the carrier signal is varied to represent data. Both peak amplitude and phase remain constant.

A) ASK

B) PSK

C) FSK-Answer

D) QAM



14. In ________, the phase of the carrier is varied to represent two or more different signal elements. Both peak amplitude and frequency remain constant.

A) ASK

B) PSK-Answer

C) FSK

D) QAM



15. A constellation diagram shows us the __________ of a signal element, particularly when we are using two carriers (one in-phase and one quadrature).

A) amplitude and phase-Answer

B) amplitude and frequency

C) frequency and phase

D) none of the above



16. Quadrature amplitude modulation (QAM) is a combination of ___________.

A) ASK and FSK

B) ASK and PSK-Answer

C) PSK and FSK

D) none of the above



17. ________ uses two carriers, one in-phase and the other quadrature.

A) ASK

B) PSK

C) FSK

D) QAM-Answer



18. _________ conversion is the representation of analog information by an analog signal.

A) Digital-to-analog

B) Analog-to-analog-Answer

C) Analog-to-digital

D) Digital-to-digital



19. Analog-to-analog conversion is needed if the available bandwidth is _______.

A) low-pass

B) band-pass-Answer

C) either (a) or (b)

D) neither (a) nor (b)



20. Which of the following is not an analog-to-analog conversion?

A) AM

B) PM

C) FM

D) QAM-Answer



21. In _____ transmission, the carrier signal is modulated so that its amplitude varies with the changing amplitudes of the modulating signal.

A) AM-Answer

B) PM

C) FM

D) none of the above



22. In _____ transmission, the frequency of the carrier signal is modulated to follow the changing voltage level (amplitude) of the modulating signal. The peak amplitude and phase of the carrier signal remain constant, but as the amplitude of the information signal changes, the frequency of the carrier changes correspondingly.

A) AM

B) PM

C) FM-Answer

D) none of the above



23. In _____ transmission, the phase of the carrier signal is modulated to follow the changing voltage level (amplitude) of the modulating signal.

A) AM

B) PM-Answer

C) FM

D) none of the above



24. In _______, the peak amplitude of one signal level is 0; the other is the same as the amplitude of the carrier frequency.

A) PSK

B) OOK-Answer

C) FSK

D) none of the above



25. How many carrier frequencies are used in BASK?

A) 2

B) 1-Answer

C) 0

D) none of the above



26. How many carrier frequencies are used in BFSK?

A) 2-Answer

B) 1

C) 0

D) none of the above



27. How many carrier frequencies are used in BPSK?

A) 2

B) 1-Answer

C) 0

D) none of the above



28. How many carrier frequencies are used in QPSK?

A) 2-Answer

B) 1

C) 0

D) none of the above



29. The constellation diagram of BASK has ______ dots.

A) 2-Answer

B) 1

C) 0

D) none of the above



30. The constellation diagram of BPSK has ______ dots.

A) 2-Answer

B) 1

C) 0

D) none of the above



31. The constellation diagram of QPSK has ______ dots.

A) 2

B) 1

C) 4-Answer

D) none of the above



32. The constellation diagram of 16-QAM has ______ dots.

A) 4

B) 16-Answer

C) 8

D) none of the above



33. The Federal Communications Commission (FCC) allows ______kHz for each AM station.

A) 5

B) 10-Answer

C) 20

D) none of the above



34. The Federal Communications Commission (FCC) allows ______ kHz for each FM station.

A) 20

B) 100

C) 200

D) none of the above

Power Semiconductors Solved Objective Questions: 

[1] Which of the following statements are correct?
1. Thyristor is current driven device
2. GTO is current driven device
3. GTR is current driven device
4. SCR is a pulse triggered device
A.1 and 2
B.1, 2, 3
C.All
D.4 only


Ans:C

[2] Which of the following statements are correct?
GTO is a pulse triggered device
MOSFET is uni-polar device
SCR is a bipolar device
Continuous gate signal is not required to maintain the SCR to be in ON state
A. 1, 2, 4 only
B. 1, 2 only
C. 4 only
D. All

Ans: D

[3] Which of the following is not a fully controlled semiconductor device?
a. MOSFET
b. IGBT
c. IGCT
d. SCR


Ans: D . Only turn on of the SCR can be controlled whereas in other devices we can control both turn on and turn off

[4] Which of the following is not associated with p-n junction
A. junction capacitance
B. charge storage capacitance
C. depletion capacitance
D. channel length modulation

Ans: D

[5] In a p-n junction diode under reverse bias, the magnitude of electric field is maximum at
A. the edge of the depletion region on the p-side
B. the edge of the depletion region on the n-side
C. the p-n junction
D. the center of the depletion region on the n-side

Ans: C

[6] An n-channel JFET has IDSS=2mA, and Vp=-4V. Its transconductance gm=(in mA/V) for an applied gate to source voltage VGS=-2V is
A. 0.25
B. 0.5
C. 0.75
D. 1

Ans: B

[7]The MOSFET switch in its on-state may be considered equivalent to
A. resistor
B. inductor
C. capacitor
D. battery

Ans: C

[8] The effective channel length of a MOSFET in a saturation decreases with increase in
A. gate voltage
B. drain voltage
C. source voltage
D. body voltage


Ans:B

[9] The early effect in a bipolar junction transistor is caused by
A. Fast turn - on
B. Fast turn - off
C. Large collector - base reverse bias
D. Large emmiter - base forward bias

Ans: C

[10] MOSFET can be used as a
A. Current controlled capacitor
B. Voltage controlled capacitor
C. Current controlled inductor
D. Voltage controlled inductors
Ans: B

Transformers objective type questions

[1] The ordinary two winding transformer's primary and secondary windings always have
A. different no of turns
B. same size of copper wire
C. a common magnetic circuit
D. separate magnetic circuits

Ans: C
[2] No load test on a transformer is carried out to find
A. copper loss
B. magnetising current
C. magnetising current and no load loss
D. efficiency of the transformer

Ans:C
[3] Transformers are rated in KVA instead of KW because
A. load power factor is often not known
B. KVA is fixed whereas KW depends on load power factor
C. Total transformer loss depends on volt ampere
D. It has become customary

Ans: C
[4] Transformer cores are laminated in order to
A. simplify its construction
B. minimise eddy current loss
C. reduce cost
D. reduce hysteresis loss

Ans: B
[5] A step up transformer increases
A. voltage
B. current
C. power
D. frequency

Ans: A
[6] In a two winding transformer, the primary and secondary induced emf E1 & E2 are always
A. equal in magnitude
B. anti phase with each other
C. in phase with each other
D. determined by load on transformer secondary

Ans:C
[7] In a transformer, the leakage flux of each winding is proportional to the current in that winding because
A. Ohm's law applies to magnetic circuits
B. Leakage paths do no saturate
C. the two windings are electrically isolated
D. mutual flux is confined to the core

Ans: B
[8] In a two winding transformer, the emf /turn in secondary winding is always......the induced emf power turn in primary
A. equal to k times
B. equal to 1/k times
C. equal
D. greater than

Ans:C
[9] In transformer terminology, the ratio 20:1 indicates that
A. there are 20 turns on primary one turn on secondary
B. secondary voltage is 1/20th of the primary
C. primary current is 20 times greater than the secondary current
D. for every 20 turns on primary, there is one turn on secondary

Ans: B
[10] In performing the short circuit test of a transformer
A. high voltage is usually short circuited
B. low voltage side is usually short circuited
C. any side is short circuited with preference
D. none of the above

Ans: B