Electronics and Communication questions reward anyone who is comfortable moving between the time domain and the frequency domain. This set covers network theory, analog and digital circuits, signals and systems, control systems, communication systems, and electromagnetics. Numerical solutions keep the units visible at every step, since a dropped factor is the most common reason a correct method still produces a wrong option.
Gray code (Reflected Binary Code) is designed such that successive values differ by only one bit. This is useful in error detection and mechanical encoders.
Q.6Easy
A multiplexer with 8 inputs requires how many select lines?
Answer: B
For n select lines, 2^n inputs are possible. For 8 inputs: 2^n = 8, so n = 3. An 8:1 multiplexer needs 3 select lines (A, B, C).
Q.7Easy
The BCD equivalent of decimal 47 is:
Answer: A
In BCD, each decimal digit is converted separately to 4-bit binary. 4 = 0100, 7 = 0111. So 47 in BCD = 0100 0111.
Q.8Easy
A full adder has how many inputs and outputs?
Answer: B
Full adder has 3 inputs (A, B, Cin) and 2 outputs (Sum, Cout). It differs from half adder which has 2 inputs and 2 outputs.
Q.9Easy
A JK flip-flop with J=1, K=1 performs:
Answer: D
JK flip-flop truth table: J=0,K=0 (No change), J=1,K=0 (Set), J=0,K=1 (Reset), J=1,K=1 (Toggle). When both are 1, output toggles.
Q.10Easy
In a 4-bit ripple counter using negative edge-triggered flip-flops, if the input frequency is 16 MHz, what is the frequency at the output of the third flip-flop?
Answer: A
In a ripple counter, each flip-flop divides the frequency by 2. The third flip-flop output frequency = 16 MHz / 2³ = 816 = 2 MHz
Q.11Easy
Which logic gate produces HIGH output only when both inputs are different?
Answer: B
XOR (Exclusive OR) gate produces HIGH output when inputs are different (01 or 10). When inputs are same (00 or 11), output is LOW
Q.12Easy
A SR flip-flop with S=0, R=0 results in:
Answer: C
When S=0 and R=0, the SR flip-flop holds its previous state. No change occurs because neither set nor reset is activated
A 3-to-8 decoder has how many output lines, and what is the number of active outputs for any single input combination?
Answer: A
A 3-to-8 decoder has 2³ = 8 output lines. For any valid input combination, exactly 1 output line is activated (HIGH), while others remain LOW
Q.15Easy
In VHDL, what does the 'rising_edge' function detect?
Answer: B
'rising_edge' detects a transition from LOW (0) to HIGH (1) on a signal, commonly used in synchronous designs to trigger actions on positive clock edges
Q.16Easy
Which of the following is NOT a characteristic of ROM (Read-Only Memory)?
Answer: B
Standard ROM is programmed during manufacturing and cannot be reprogrammed by users. PROM, EPROM, and EEPROM allow user programming, but basic ROM does not
Q.17Easy
In a 16×4 RAM, what do the numbers 16 and 4 represent respectively?
Answer: D
16×4 RAM means 16 memory words (locations), each storing 4 bits of data. This requires log₂(16)=4 address lines. Total capacity = 16 words × 4 bits = 64 bits
Q.18Easy
What is the fundamental difference between combinational and sequential circuits?
Answer: B
Combinational circuits: output = f(present inputs only). Sequential circuits: output depends on present inputs AND past states (memory elements like flip-flops store history)
Q.19Easy
Which of the following is a characteristic of asynchronous counters?
Answer: B
Asynchronous (ripple) counters work by cascading flip-flops where the output of one flip-flop triggers the next, creating a ripple effect.
Q.20Easy
A BCD counter counts from 0 to 9 and then resets. How many flip-flops are minimum required?
Answer: C
BCD (Binary Coded Decimal) requires 4 bits to represent decimal digits 0-9 (2^4 = 16 combinations, but only 10 are used).
