Junior Engineer (Electrical/Electronics) MCQs – Series 6 (Q71-80)
Q71. The NAND gate is called a universal gate because:
- A) It can only perform the AND operation
- B) Any logic function can be implemented using only NAND gates
- C) It only works in analog circuits
- D) It has the lowest power consumption of all gates
Answer: B
NAND (and NOR) gates are functionally complete — any Boolean function, including AND, OR, and NOT, can be built using only NAND gates.
Q72. The decimal equivalent of the binary number 1011 is:
Answer: D
1011₂ = 1×8 + 0×4 + 1×2 + 1×1 = 8+0+2+1 = 11.
Q73. A JK flip-flop with both J and K inputs held at logic 1 will:
- A) Remain in a no-change (hold) state
- B) Reset its output to 0
- C) Toggle its output on each clock pulse
- D) Set its output to 1
Answer: C
When J=K=1, the JK flip-flop toggles state (Q → Q’) on every active clock edge, resolving the ambiguity present in the SR flip-flop.
Q74. The minimum number of flip-flops required to design a MOD-16 counter is:
Answer: D
A MOD-N counter requires n flip-flops such that 2ⁿ ≥ N; for N=16, n=4 since 2⁴=16.
Q75. In Boolean algebra, the simplified form of the expression A + A’B is:
- A) A + B
- B) A
- C) A’B
- D) AB
Answer: A
Using the absorption/identity laws: A + A’B = (A+A’)(A+B) = 1·(A+B) = A+B.
Q76. A multiplexer is a combinational circuit that:
- A) Selects one of many input signals and routes it to a single output line
- B) Generates timing/clock pulses
- C) Converts serial data into parallel data
- D) Stores binary data permanently
Answer: A
A multiplexer (MUX) uses select lines to choose one of several data inputs to connect to a single output.
Q77. The 2’s complement of the binary number 1010 is:
- A) 1011
- B) 0110
- C) 0101
- D) 1001
Answer: B
1’s complement of 1010 is 0101; adding 1 gives 0110, which is the 2’s complement.
Q78. In a D flip-flop, after an active clock edge, the output Q becomes equal to:
- A) Always logic 0
- B) Always logic 1
- C) The value present at the D input just before the clock edge
- D) The previous output value, unchanged
Answer: C
A D flip-flop simply transfers (‘latches’) the D input value to Q at the triggering clock edge.
Q79. Which logic family is known for very low static power consumption, making it widely used in battery-operated digital devices?
- A) CMOS
- B) ECL
- C) RTL
- D) TTL
Answer: A
CMOS logic draws negligible static current because complementary MOSFETs are never both fully on simultaneously in steady state, giving very low power dissipation.
Q80. A half adder circuit is a combinational circuit that adds:
- A) Two bits without considering any carry input
- B) Four bits simultaneously
- C) Two bits including a carry input from a previous stage
- D) Three bits simultaneously
Answer: A
A half adder produces SUM and CARRY outputs for two single input bits only, with no provision for an incoming carry (that is the job of a full adder).
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