DIGITAL ELECTRONICS 2026 – LOGIC GATES, MICROPROCESSORS & VERIFIED PRACTICE EXAM GUIDE

DIGITAL ELECTRONICS 2026 – LOGIC GATES,
MICROPROCESSORS & VERIFIED PRACTICE
EXAM GUIDE
Question 1 What is the output of an AND gate when both inputs are 1?
A) 0

B) 1 CORRECT ANSWER
C) Undefined

D) High impedance

RATIONALE: An AND gate outputs 1 only when ALL inputs are 1. Since both inputs are 1,
the output is 1.



Question 2 Which logic gate produces a HIGH output only when all inputs are LOW?

A) AND

B) OR

C) NOR CORRECT ANSWER
D) NAND

RATIONALE: A NOR gate is an OR gate followed by a NOT gate. It outputs HIGH (1) only
when ALL inputs are LOW (0).



Question 3 What is the Boolean expression for a NAND gate with inputs A and B?
A) A · B

B) A + B

**C) 𝐴 ‾⋅ 𝐵** *CORRECT ANSWER*
‾ 𝐵
D) 𝐴 +

RATIONALE: NAND means NOT-AND. The Boolean expression is the complement of the
AND operation: 𝐴 ‾⋅ 𝐵.



Question 4 Which gate is known as the "universal gate"?

,A) AND

B) OR

C) XOR

D) NAND CORRECT ANSWER

RATIONALE: NAND (and NOR) are called universal gates because any other logic gate can
be constructed using only NAND gates.



Question 5 What is the output of an XOR gate when both inputs are the same?

A) 0 CORRECT ANSWER
B) 1

C) Depends on the inputs
D) High impedance

RATIONALE: XOR (Exclusive OR) outputs 1 only when inputs are DIFFERENT. When both
inputs are the same (00 or 11), the output is 0.


Question 6 De Morgan's first theorem states:

A) 𝐴 ‾⋅ 𝐵 = 𝐴‾ ⋅ 𝐵‾

**B) 𝐴 ‾⋅ 𝐵 = 𝐴‾ + 𝐵‾** *CORRECT ANSWER*
‾ 𝐵 = 𝐴‾ + 𝐵‾
C) 𝐴 +

D) 𝐴 ⋅ 𝐵 = 𝐴 + 𝐵

RATIONALE: De Morgan's first theorem states that the complement of a product equals the
sum of the complements: 𝐴 ‾⋅ 𝐵 = 𝐴‾ + 𝐵‾.



Question 7 What is the output of a NOT gate when the input is 0?

A) 1 CORRECT ANSWER
B) 0
C) Undefined

,D) Same as input

RATIONALE: A NOT gate (inverter) complements the input. When input is 0, the output is 1.


Question 8 Which Boolean law states that A + A = A?

A) Complement law
B) Commutative law

C) Idempotent law CORRECT ANSWER
D) Absorption law

RATIONALE: The Idempotent law states that OR-ing or AND-ing a variable with itself gives
the same variable: A + A = A and A · A = A.


Question 9 The truth table for a 2-input OR gate has how many rows?

A) 2

B) 3

C) 4 CORRECT ANSWER
D) 8

RATIONALE: For n inputs, a truth table has 2ⁿ rows. For 2 inputs: 2² = 4 rows.


Question 10 What does the XNOR gate produce when inputs are equal?

A) 1 CORRECT ANSWER
B) 0

C) Undefined
D) Inverted input

RATIONALE: XNOR (Exclusive NOR) is the complement of XOR. It outputs 1 when inputs
are the SAME, making it an "equality detector."

, Question 11 Which Boolean expression represents the absorption law?

A) A + 0 = A

B) A + (A · B) = A CORRECT ANSWER
C) A · 1 = A

D) A + A' = 1

RATIONALE: The absorption law states A + (A · B) = A. The variable A "absorbs" the term
A·B, simplifying the expression.



Question 12 A 3-input AND gate outputs 1 when:
A) At least one input is 1

B) Exactly one input is 1

C) All three inputs are 1 CORRECT ANSWER
D) At least two inputs are 1

RATIONALE: An AND gate, regardless of the number of inputs, outputs HIGH (1) only when
ALL inputs are HIGH (1).



Question 13 Which gate produces a LOW output only when all inputs are HIGH?

A) OR

B) NOR

C) NAND CORRECT ANSWER
D) AND

RATIONALE: A NAND gate outputs LOW (0) only when ALL inputs are HIGH (1). For all
other input combinations, the output is HIGH.



Question 14 What is the minimum number of NAND gates needed to implement a NOT gate?

A) 1 CORRECT ANSWER
B) 2