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.
Clamping diodes protect circuits by limiting the maximum voltage that can be applied to a node. They conduct when voltage exceeds V_DD + V_D_forward or goes below V_SS - V_D_forward, preventing overstress to gate oxide and junctions.
Q.22Easy
A Zener diode is operating in reverse breakdown with a current of 50 mA. If the Zener resistance is 5 Ω and Zener voltage is 12 V, what is the terminal voltage?
Answer: A
Terminal voltage = Vz + Iz·Rz = 12 + (50×10^-3 × 5) = 12 + 0.25 = 12.25 V
Q.23Easy
In a BJT, if the base-emitter junction is forward biased and the base-collector junction is also forward biased, the transistor is operating in which region?
Answer: B
When both junctions are forward biased, the transistor operates in saturation region where collector current is maximum and relatively independent of base current.
Q.24Easy
In a photodiode, the photocurrent is primarily determined by which parameter?
Answer: A
Photocurrent Iph = η·(q/hf)·Φ, where η is quantum efficiency and Φ is incident optical power.
Q.25Easy
In a JFET, as the reverse bias voltage on the gate-source junction increases, what happens to the channel width?
Answer: B
The depletion region widens with more negative VGS, pinching off the channel and reducing ID until pinch-off voltage is reached.
Q.26Easy
In a p-channel MOSFET, if VGS = -8 V and VT = -2 V, what is the gate-source overdrive voltage?
Answer: A
For p-channel: |VGS - VT| = |-8 - (-2)| = |-6| = 6 V overdrive, or algebraically VGS - VT = -8 - (-2) = -6 V
Q.27Easy
A power MOSFET has RDS(on) = 0.5 Ω and carries 20 A. What is the approximate conduction power loss?
Answer: B
Pconduction = ID²·RDS(on) = (20)²×0.5 = 400×0.5 = 200 W
Q.28Easy
Which semiconductor material has the highest electron mobility among common choices?
Answer: A
GaAs has electron mobility ~8500 cm²/Vs, significantly higher than Si (~1350 cm²/Vs), enabling higher frequency operation.
Q.29Easy
In a silicon p-n junction diode at room temperature (T = 300K), the thermal voltage (VT) is approximately:
Answer: A
Thermal voltage VT = kT/q, where k = 1.38×10⁻²³ J/K, T = 300K, q = 1.6×10⁻¹⁹ C. VT ≈ 26 mV at room temperature, a fundamental parameter in semiconductor device physics.
Q.30Easy
Which of the following is NOT a basic logic gate?
Answer: C
XOR is a derived logic gate made from combination of basic gates (AND, OR, NOT). The three basic gates are AND, OR, and NOT.
Q.31Easy
The output of a NAND gate is 0 when:
Answer: B
NAND gate output is 0 only when all inputs are 1. NAND is NOT of AND operation. For 2-input: output is 0 only when both inputs are 1.
Q.32Easy
How many 2-input NAND gates are required to implement a 2-input AND gate?
Answer: B
AND gate can be implemented using two NAND gates. First NAND gate as AND, second NAND gate as NOT (both inputs same) to negate the output.
Q.33Easy
The decimal equivalent of binary number 10110.101 is:
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.35Easy
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.36Easy
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.37Easy
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.38Easy
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.39Easy
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.40Easy
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
