# Multiple Choice Questions and Answers on Signals and Switches

Q1. The serial format for transmitting binary information uses:

a) a single conductor
b) multiple conductors
c) infrared technology
d) fiber-optic

Q2. Which device(s) have almost ideal ON and OFF resistances?

a) electromechanical relays
b) manual switches
c) semiconductor devices (diodes and transistors)
d) electromechanical relays and manual switches

Q3. A diode placed in parallel across a relay coil serves what function?

a) to regulate input voltage
b) to protect the coil from arcing
c) to ensure most of the current passes through the coil
d) to reduce arcing across the relay contacts

Q4. Serial communication can be sped up by:

a) using silver or gold conductors instead of copper
b) using high-speed clock signals
c) adjusting the duty cycle of the binary information
d) using silver or gold conductors instead of copper and high-speed clock signals

Q5. What is the period of a clock waveform that has a frequency of 15.4 kHz?

a) 649 μs
b) 6.49 μs
c) 64.9 μs
d) 0.649 μs

Q6. How long will it take to serially transmit the hexadecimal number C316 if the clock frequency is 1.5 MHz?

a) 4.69 ms
b) 4.69 μs
c) 5.33 ms
d) 5.33 μs

Q7. What is the output voltage from the circuit in the given figure?

a) +15 V
b) +12 V
c) +3 V
d) 0 V

Q8. The family of logic that is composed of bipolar junction transistors is ____.

a) TTL
b) CMOS
c) DIP
d) BJT

Q9. What can a relay provide between the triggering source and the output that semiconductor switching devices cannot?

a) total isolation
b) faster
c) higher current rating
d) total isolation and higher current rating

Q10. Determine the output voltage Vout for the circuit in the given figure.

a) –0.5 V
b) 0 V
c) +5 V
d) +4.3 V

Q11. Why is parallel data transmission preferred over serial data transmission for most applications?

a) It is much slower.
b) It is cheaper.
c) More people use it.
d)It is much faster.

Q12. Determine if diodes D1 and D2 in the given figure are forward or reverse biased.

a) D1 forward and D2 reverse
b) D2 forward and D1 reverse
c) D1 and D2 reverse
d) D1 and D2 forward

Q13. With surface-mount technology (SMT), the devices should:

a) utilize transistor outline connections
b) mount directly
c) have parallel connecting pins

Q14. To forward bias a diode, a ________ potential is needed on the ________ and a ________ is needed on the ________.

a) negative, cathode, positive, anode
b) negative, anode, positive, cathode

Q15. Why, in most applications, are transistor switches used in place of relays?

a) They consume less power.
b) They are faster.
c) They are quieter and smaller.
d) all of the above

Q16. Internally, a computer’s binary data are almost always transmitted on parallel channels, commonly referred to as the:

a) parallel bus
b) serial bus
c) data bus
d) memory bus

Q17. The hexadecimal number 4B16 is transmitted as an 8-bit word in parallel. What is the time required for this transmission if the clock frequency is 2.25 MHz?

a) 444 ns
b) 444 μs
c) 3.55 μs
d) 3.55 ms

Q18. Why is the given circuit called an inverter?

a) The output is the opposite (inverse) of the input.
b) The output is in phase with the input.
c) The output is the same as the input.
d) There is no output.

Q19. What is the frequency of a clock waveform if the period of that waveform is 1.25 μs ?

a) 8 kHz
b) 0.8 kHz
c) 0.8 MHz
d) 8 MHz

Q20. Why does the TTL family use a totem-pole circuit on the output?

a) It provides active pull-up.
b) It provides active pull-down.
c) It provides active pull-up and active pull-down.
d) None of the above

Q21. Determine the voltage on the collector Vc of the given transistor circuit.

a) 0 V
b) +10 V
c) +4.7 V
d) +0.5 V

Q22. The period of a waveform is the percentage of time the signal is HIGH.

a) True
b) False

Q23. What is a disadvantage of CMOS in place of TTL?

a) It switches slower.
b) It uses less power.
c) It is smaller.
d) cost

Q24. The units for the HIGH time for a periodic wave are ________.

a) seconds
b) hertz
c) cycles
d) %

Q25. What is the minimum voltage required before a diode will allow current to flow between the cathode and the anode?

a) 0.7 V
b) 0.07 V
c) 4.3 V
d) 0.2 V

Q26. What is the advantage of using serial data transmission over parallel data transmission?

a) It is slower.
b) Only one pair of wires is required.
c) More people use it.
d) It is faster.

Q27. A TTL totem-pole circuit is designed so that the output transistors:

a) are always on together
b) provide phase splitting
c) provide voltage regulation
d) are never on together

Q28. What is the advantage of using CMOS logic over TTL?

a) It switches faster.
b) It uses less power.
c) It is larger.
d) cost

Q29. What is used to graphically show the time relationship between two or more digital waveforms?

a) reference diagram
b) timing diagram
c) voltage curve

Q30. If the input voltage on the base of the transistor in the given figure is changed to +10 V, what is the new voltage at the collector Vc?

a) Not enough information is provided.
b)Vc = 10 V
c)Vc = 0 V
d)Vc = 5 V

Q31. Is the transistor in the given figure considered ON or OFF?

a) OFF
b) ON

Q32. Normal operation of an NPN bipolar transistor requires the base to be ________ with respect to the emitter, and ________ with respect to the collector.

a) positive, negative
b) positive, positive
c) negative, positive
d) negative, negative

Q33. The abbreviation NO, when used with respect to electromechanical relays, stands for not operational.

a) True
b) False

Q34. In a graphical representation of voltage versus time, ________ is displayed on the ________ axis and ________ is displayed on the ________ axis.

a) time, y, voltage, x
b) voltage, y, time, x

Q35. TTL logic chips must have connections to Vcc and ground, even if all inputs and outputs are properly used and tied to valid signals.

a) True
b) False

Q36. What is the output voltage Vout for the given circuit if the input voltage changes to 0 V?

a) +12 V
b) +15 V
c) +3 V
d) 0 V

Q37. If the input voltage on D1 in the given figure is changed to 0 V, what is the output voltage Vout?

a) –5 V
b)0 V
c)+5 V
d) +4.3 V

Q38. An indication of cutoff in an NPN bipolar transistor is that the:

a) collector current is maximum
b) collector-to-emitter voltage equals zero
c) base-to-emitter voltage equals 0.7 V
d) collector to emitter appears to be open