Digital Electronics Logic Gates Questions and Answers

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Q21
How many inputs of a four-input AND gate must be HIGH in order for the output of the logic gate to go HIGH?
  • A any one of the inputs
  • B any two of the inputs
  • C any three of the inputs
  • D all four inputs
Answer: Option D
Q22
If the output of a three-input AND gate must be a logic LOW, what must the condition of the inputs be?
  • A All inputs must be LOW.
  • B All inputs must be HIGH.
  • C At least one input must be LOW.
  • D At least one input must be HIGH.
Answer: Option C
Q23
Logically, the output of a NOR gate would have the same Boolean expression as a(n):
  • A NAND gate immediately followed by an inverter
  • B OR gate immediately followed by an inverter
  • C AND gate immediately followed by an inverter
  • D NOR gate immediately followed by an inverter
Answer: Option B
Q24
A logic probe is placed on the output of a gate and the display indicator is dim. A pulser is used on each of the input terminals, but the output indication does not change. What is wrong?
  • A The dim indication on the logic probe indicates that the supply voltage is probably low.
  • B The output of the gate appears to be open.
  • C The dim indication is the result of a bad ground connection on the logic probe.
  • D The gate is a tristate device.
Answer: Option B
Q25
What is the Boolean expression for a three-input AND gate?
  • A X = A + B + C
  • B X = A · B · C
  • C A – B – C
  • D A $ B $ C
Answer: Option B
Q26
Which of the following gates has the exact inverse output of the OR gate for all possible input combinations?
  • A NOR
  • B NOT
  • C NAND
  • D AND
Answer: Option A
Q27
What is the difference between a 7400 and a 7411 IC?
  • A 7400 has two four-input NAND gates; 7411 has three three-input AND gates
  • B 7400 has four two-input NAND gates; 7411 has three three-input AND gates
  • C 7400 has two four-input AND gates; 7411 has three three-input NAND gates
  • D 7400 has four two-input AND gates; 7411 has three three-input NAND gates
Answer: Option B
Q28
The output of an exclusive-OR gate is HIGH if ________.
  • A all inputs are LOW
  • B all inputs are HIGH
  • C the inputs are unequal
  • D none of the above
Answer: Option C
Q29
A clock signal with a period of 1 s is applied to the input of an enable gate. The output must contain six pulses. How long must the enable pulse be active?
  • A Enable must be active for 0 s.
  • B Enable must be active for 3 s.
  • C Enable must be active for 6 s.
  • D Enable must be active for 12 s.
Answer: Option C
Q30
The AND function can be used to ________ and the OR function can be used to ________ .
  • A enable, disable
  • B disable, enable
  • C enable or disable, enable or disable
  • D detect, invert
Answer: Option C

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