Multivibrators and 555 Timer Questions and Answers
Multivibrators and 555 Timer questions with answers help electronics aspirants strengthen their understanding of pulse generation and timing circuits. The 555 timer IC is widely used in monostable, astable, and bistable multivibrator configurations, making it a frequent topic in exams like DRDO, ISRO, and GATE. Mastering these circuits enhances conceptual clarity in waveform generation, duty cycle control, and timing applications. This section provides well-explained aptitude questions and answers that simulate actual electronics exams, helping students test their theoretical knowledge through practical problem-solving. Whether preparing for technical interviews or competitive electronics tests, this topic gives you an edge through step-by-step solutions and real-world applications of timing circuits.
Multivibrators and 555 Timer
1. What is the function of the comparators in the 555 timer circuit?
- to compare the output voltages to the internal voltage divider
- to compare the input voltages to the internal voltage divider
- to compare the output voltages to the external voltage divider
- to compare the input voltages to the external voltage divider
2. When a capacitor charges:
- the voltage across the plates rises exponentially
- the circuit current falls exponentially
- the capacitor charges to the source voltage in 5×RC seconds
- all of the above
3. The ________ is defined as the time the output is active divided by the total period of the output signal.
- on time
- off time
- duty cycle
- active ratio
4. 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?
- 0.44 ms
- 0.501 ms
- 0.66 ms
- 0.70 ms
5. What does the discharge transistor do in the 555 timer circuit?
- charge the external capacitor to stop the timing
- charge the external capacitor to start the timing over again
- discharge the external capacitor to stop the timing
- discharge the external capacitor to start the timing over again
6. Pulse stretching, time-delay, and pulse generation are all easily accomplished with which type of multivibrator circuit?
- astable
- monostable
- multistable
- bistable
7. 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 comparator
- a voltage amplifier
- two comparators
- a peak detector
8. With most monostable multivibrators, what is the Q output when no input trigger has occurred?
- LOW
- +5 V
- SET
- HIGH
9. An astable multivibrator requires:
- balanced time constants
- a pair of matched transistors
- no input signal
- dual J-K flip-flops
10. A crystal demonstrates the ________ effect when a mechanical force across the crystal causes a small voltage to be generated.
- photoelectric
- Co-pitts
- piezoelectric
- flywheel