21. Which devices are used as indicators in a digital system?
A. LCD
B. LED
C. Varactor diode
D. Gunn diode
Answer: b
The light-emitting diodes are used as indicators in the digital system and can be directly driven by a logic output.
22. How is the biasing done in LEDs?
A. forward bias
B. no bias
C. supply voltage
D. reverse bias
Answer: d
The LEDs will light up only when the diode reverse breakdown is achieved. It is usually about 2 to 2.2V.
23. Which of the following determines the brightness of LEDs?
A. current
B. voltage
C. resistance
D. conductance
Answer: A
The current drive determines the brightness of the LEDs and it is usually associated with a current limiting resistor in series with the LED to prevent the overheating.
24. Which of the following is a current limiting device?
A. voltage
B. current
C. buffer
D. inductor
Answer: C
A buffer can be used as a current limiting device. Similarly, a transistor can also be used as a current limiting device.
25. Which of the following can switch the current by a make or break contact?
A. transistor
B. relay
C. buffer
D. fet
Answer: B
The relays are a kind of switching power in which the logic signal is used to energize the relay. The relay contacts are broken or made accordingly and help in switching the current.
26. Which of the following generates a back EMF?
A. relay
B. buffer
C. transistor
D. FET
Answer: A
The relay generates a back voltage across its terminals when the logic output switches from a high to a low state.
27. Which of the following is used to avoid the back EMF in the relay?
A. resistor
B. capacitor
C. inductor
D. diode
Answer:d
In order to get rid of the back EMF which is generated by the relay, a diode is connected across the terminals which operate in the reverse bias so that nothing can harm the relay.
28. Which of the following can provide a speed control technique in the DC motor interfacing?
A. PCM
B. DPCM
C. ADPCM
D. PWM
Answer: D
The pulse width modulation can provide a speed control technique in the DC motor interfacing by changing its mark/space ratio.
29. Which of the following possesses some loops for providing timing functions?
A. hardware
B. software
C. timer
D. counter
Answer: B
In the software system, certain loops perform the timing functions. A program is created to switch the motor on and it will start counting through a delay loop. When the count is finished, the motor is switched off. In the second delay loop, it can determine the motor-off period.
30. Which signal is sampled at regular intervals for the purpose of ADC?
A. analog signal
B. digital signal
C. quantized signal
D. sampled signal
Answer: A
The analog signal is sampled at regular intervals for the analog to digital conversion. Each sample is then quantized to divided by a given value in order to identify the number of approximate analog values.
