MCQOPTIONS
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MCQOPTIONS
This section includes 53 Mcqs, each offering curated multiple-choice questions to sharpen your Digital Electronics knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
The internal circuitry of the 555 timer consists of ________, an flip-flop, a transistor switch, an output buffer amplifier, and a voltage divider. |
| A. | a comparator |
| B. | a voltage amplifier |
| C. | two comparators |
| D. | a peak detector |
| Answer» D. a peak detector | |
| 2. |
With most monostable multivibrators, what is the output when no input trigger has occurred? |
| A. | LOW |
| B. | +5 V |
| C. | SET |
| D. | HIGH |
| Answer» B. +5 V | |
| 3. |
The bistable multivibrator is an flip-flop. |
| A. | True |
| B. | False |
| Answer» C. | |
| 4. |
The 74S124 TTL chip is a voltage-controlled oscillator that will generate a specific frequency at . |
| A. | True |
| B. | False |
| Answer» C. | |
| 5. |
A 0.3-F capacitor has an initial charge of 2.7 V. If it is discharged through a 10-k resistor for 6.5 ms, how much voltage will be left across the capacitor? |
| A. | 0.0 V |
| B. | 0.309 V |
| C. | 2.7 V |
| D. | 2.295 V |
| Answer» C. 2.7 V | |
| 6. |
A 22-k resistor and a 0.02-F capacitor are connected in series to a 5-V source. How long will it take the capacitor to charge to 3.4 V? |
| A. | 0.44 ms |
| B. | 0.501 ms |
| C. | 0.66 ms |
| D. | 0.70 ms |
| Answer» C. 0.66 ms | |
| 7. |
A multivibrator is a circuit that changes between two digital levels on a continuous, free-running basis or on demand. |
| A. | 1 |
| B. | |
| Answer» B. | |
| 8. |
When the 74123, a retriggerable monostable multivibrator device, ends its timing cycle it must be started all over again. |
| A. | 1 |
| B. | |
| Answer» C. | |
| 9. |
Timing accuracy of more than eight significant digits can be easily achieved by using quartz crystals. |
| A. | 1 |
| B. | |
| Answer» C. | |
| 10. |
A monostable multivibrator is commonly called a two shot. |
| A. | 1 |
| B. | |
| Answer» C. | |
| 11. |
In a typical IC monostable multivibrator circuit, at the falling edge of the trigger input, the output switches HIGH for a period of time determined by the ________. |
| A. | value of the RC timing components |
| B. | amplitude of the input trigger |
| C. | frequency of the input trigger |
| D. | magnitude of the dc supply voltage |
| Answer» B. amplitude of the input trigger | |
| 12. |
A single Schmitt trigger inverter is all that is needed to build a simple astable multivibrator. |
| A. | 1 |
| B. | |
| Answer» C. | |
| 13. |
A crystal demonstrates the ________ effect when a mechanical force across the crystal causes a small voltage to be generated. |
| A. | photoelectric |
| B. | Co-pitts |
| C. | piezoelectric |
| D. | flywheel |
| Answer» D. flywheel | |
| 14. |
A comparator simply outputs a HIGH or LOW based on a comparison of the voltage levels at its input. |
| A. | 1 |
| B. | |
| Answer» B. | |
| 15. |
What is another name for a bistable multivibrator? |
| A. | an on-off switch |
| B. | an oscillator |
| C. | a flip-flop |
| Answer» D. | |
| 16. |
Determine tHI and tLO for the circuit given below. |
| A. | tHI = 7.95 s, tLO = 6.24 s |
| B. | tHI = 6.24 s, tLO = 7.95 s |
| C. | tHI = 3.97 s, tLO = 3.21 s |
| D. | tHI = 3.21 s, tLO = 3.97 s |
| Answer» B. tHI¬†=¬†6.24 s, tLO¬†=¬†7.95 s | |
| 17. |
Triggering a retriggerable one shot during pulse generation will: |
| A. | time out the original pulse |
| B. | extend the pulse to this trigger width |
| C. | have no effect |
| D. | double the original pulse width |
| Answer» C. have no effect | |
| 18. |
What is the output pulse width of the waveform at the output of the circuit in the given figure? |
| A. | 1.65 ms |
| B. | 18.2 ms |
| C. | 4.98 ms |
| D. | 54.6 ms |
| Answer» C. 4.98 ms | |
| 19. |
The internal circuitry of the 555 timer consists of ________, an R-S flip-flop, a transistor switch, an output buffer amplifier, and a voltage divider. |
| A. | a comparator |
| B. | a voltage amplifier |
| C. | two comparators |
| D. | a peak detector |
| Answer» D. a peak detector | |
| 20. |
What controls the output pulse width of a one shot? |
| A. | the clock frequency |
| B. | the width of the clock pulse |
| C. | an RL time constant |
| D. | an RC time constant |
| Answer» E. | |
| 21. |
An astable multivibrator requires: |
| A. | balanced time constants |
| B. | a pair of matched transistors |
| C. | no input signal |
| D. | dual J-K flip-flops |
| Answer» D. dual J-K flip-flops | |
| 22. |
A retriggerable one shot has a pulse of 10 ms. 3 ms after being triggered, another trigger pulse is applied. The resulting output pulse will be ________ ms. |
| A. | 3 |
| B. | 7 |
| C. | 10 |
| D. | 13 |
| Answer» E. | |
| 23. |
The 74S124 TTL chip is a voltage-controlled oscillator that will generate a specific frequency at Vout. |
| A. | 1 |
| B. | |
| Answer» C. | |
| 24. |
With most monostable multivibrators, what is the Q output when no input trigger has occurred? |
| A. | LOW |
| B. | +5 V |
| C. | SET |
| D. | HIGH |
| Answer» B. +5 V | |
| 25. |
The monostable multivibrator circuit is not an oscillator because ________. |
| A. | its output switches between two states |
| B. | it requires a trigger to obtain an output signal |
| C. | it requires a sine wave input signal |
| D. | the circuit does not require a dc power supply |
| Answer» C. it requires a sine wave input signal | |
| 26. |
The bistable multivibrator is an R-C flip-flop. |
| A. | 1 |
| B. | |
| C. | 1 |
| D. | |
| Answer» C. 1 | |
| 27. |
In the 74121, which is nonretriggerable, any triggers that come in before the end of the timing cycle are ignored. |
| A. | 1 |
| B. | |
| Answer» B. | |
| 28. |
An astable 555 timer has the following number of stable states: |
| A. | 0 |
| B. | 1 |
| C. | 2 |
| D. | 3 |
| Answer» B. 1 | |
| 29. |
Which of the following is NOT a characteristic of a retriggerable monostable multivibrator? |
| A. | It is a dual multivibrator. |
| B. | It has an active-HIGH reset, which terminates all timing functions. |
| C. | It has no internal timing resistor. |
| D. | none of the above |
| Answer» C. It has no internal timing resistor. | |
| 30. |
The pulse width out of a one-shot multivibrator increases when the: |
| A. | supply voltage increases |
| B. | timing resistor decreases |
| C. | UTP decreases |
| D. | timing capacitance increases |
| Answer» B. timing resistor decreases | |
| 31. |
If a diode is connected across resistor RB (positive end up) in the given figure, what is the new duty cycle of the output waveform? |
| A. | 0.56 |
| B. | 0.44 |
| C. | 0.216 |
| D. | 0.174 |
| Answer» D. 0.174 | |
| 32. |
Does the 74123 one shot have an internal timing resistor? |
| A. | yes |
| B. | no |
| Answer» C. | |
| 33. |
If the resistor in the Schmitt trigger astable multivibrator is a variable resistor, what part of the output voltage waveform will change when the resistance is changed? |
| A. | the shape of the waveform |
| B. | the amplitude of the waveform |
| C. | the period of the waveform |
| D. | none of the above |
| Answer» D. none of the above | |
| 34. |
To obtain a 50% duty cycle in an astable 555 timer circuit: |
| A. | tLO = tHI |
| B. | RA = RB and short RB with a diode during the capacitor charging cycle |
| C. | capacitor voltage must rise above 1/3 VCC |
| D. | tLO = tHI, RA = RB, and short RB with a diode during the capacitor charging cycle |
| Answer» B. RA = RB and short RB with a diode during the capacitor charging cycle | |
| 35. |
A monostable 555 timer has the following number of stable states: |
| A. | 0 |
| B. | 1 |
| C. | 2 |
| D. | 3 |
| Answer» C. 2 | |
| 36. |
What is the duty cycle of the waveform at the output of the circuit given below? |
| A. | 0.78 |
| B. | 0.56 |
| C. | 0.5 |
| D. | 0.44 |
| Answer» C. 0.5 | |
| 37. |
Is there any limit to the number of times that a 74123 can be retriggered? |
| A. | yes |
| B. | no |
| Answer» C. | |
| 38. |
The output of the astable circuit ________. |
| A. | constantly switches between two states |
| B. | is LOW until a trigger is received |
| C. | is HIGH until a trigger is received |
| D. | floats until triggered |
| Answer» B. is LOW until a trigger is received | |
| 39. |
Is the circuit given below an astable multivibrator or a monostable multivibrator? |
| A. | monostable |
| B. | astable |
| Answer» B. astable | |
| 40. |
Which mode of operation is being used when a 555 timer chip has two external resistors and an external capacitor? |
| A. | monostable |
| B. | pulse stretching |
| C. | Schmitt triggering |
| D. | astable |
| Answer» E. | |
| 41. |
What is the pulse width of the output of a 74123 if an external 4.7-k resistor and a 0.022-F capacitor are used? |
| A. | 290 ms |
| B. | 29 ms |
| C. | 33.3 s |
| D. | 290 s |
| Answer» D. 290 s | |
| 42. |
The ________ is defined as the time the output is active divided by the total period of the output signal. |
| A. | on time |
| B. | off time |
| C. | duty cycle |
| D. | active ratio |
| Answer» D. active ratio | |
| 43. |
What is the difference between a retriggerable one shot and a nonretriggerable one shot? |
| A. | The nonretriggerable can only be triggered once. |
| B. | The retriggerable can be triggered many times. |
| C. | The output pulse can be stretched with a nonretriggerable. |
| D. | The output pulse can be stretched with a retriggerable. |
| Answer» E. | |
| 44. |
When a capacitor charges: |
| A. | the voltage across the plates rises exponentially |
| B. | the circuit current falls exponentially |
| C. | the capacitor charges to the source voltage in 5√óRC seconds |
| D. | all of the above |
| Answer» E. | |
| 45. |
Design a circuit using a 74121 to convert a 33-kHz, 30% duty cycle waveform to a 33-kHz, 60% duty cycle waveform. |
| A. | Rint = 2 k, Cext = 0.012 nF |
| B. | Rint = 2 k, Cext = 0.012 F |
| C. | Rint = 4 k, Cext = 0.012 nF |
| D. | Rint = 4 k, Cext = 0.012 F |
| Answer» C. Rint¬†=¬†4 k, Cext¬†=¬†0.012 nF | |
| 46. |
If Vcc of a 555 timer circuit is set to +10 V what is the level of output voltage from the circuit? |
| A. | VOH = 10 V, VOL = 0 V |
| B. | VOH = 10 V, VOL = 0.1 V |
| C. | VOH = 8.5 V, VOL = 0 V |
| D. | VOH = 8.5 V, VOL = 0.1 V |
| Answer» E. | |
| 47. |
What does the discharge transistor do in the 555 timer circuit? |
| A. | charge the external capacitor to stop the timing |
| B. | charge the external capacitor to start the timing over again |
| C. | discharge the external capacitor to stop the timing |
| D. | discharge the external capacitor to start the timing over again |
| Answer» E. | |
| 48. |
A 22-k resistor and a 0.02-F capacitor are connected in series to a 5-V source. How long will it take the capacitor to charge to 3.4 V? |
| A. | 0.44 ms |
| B. | 0.501 ms |
| C. | 0.66 ms |
| D. | 0.70 ms |
| Answer» C. 0.66 ms | |
| 49. |
What is the difference between an astable multivibrator and a monostable multivibrator? |
| A. | The astable is free running. |
| B. | The astable needs to be clocked. |
| C. | The monostable is free running. |
| D. | none of the above |
| Answer» B. The astable needs to be clocked. | |
| 50. |
When extremely critical timing is required, a quartz crystal can be used. |
| A. | 1 |
| B. | |
| C. | 1 |
| D. | |
| Answer» B. | |