A wattmeter with voltage coil rating of 300 V and current coil rating of 5 A is used to measure power in a circuit. If the actual voltage is 250 V and current is 4 A at power factor 0.8, what will be the wattmeter reading if it has full-scale deflection of 1500 W?
Answer: A
Power = V × I × cos(φ) = 250 × 4 × 0.8 = 800 W. The wattmeter reading equals actual power consumed.
Q.262Medium
Which method is most suitable for measuring frequency in the range of 10 Hz to 100 kHz with high accuracy in 2024-25 standards?
Answer: B
Digital frequency counters provide accuracy of ±1 count with real-time display and are industry standard for this frequency range.
Q.263Medium
An AC bridge circuit is used to measure unknown capacitance. At balance, the product of opposite arms satisfies which condition?
Answer: C
For AC bridges at balance condition: Z₁ × Z₄ = Z₂ × Z₃, where Z represents impedance of arms.
Q.264Medium
In a megohmmeter, what voltage is typically applied across the test terminals to measure very high resistances (> 1 MΩ)?
Answer: A
Megohmmeters use high DC voltages (1-5 kV) to force sufficient current through high resistances for measurable deflection.
Q.265Medium
A standard cell has an EMF of 1.0186 V at 20°C with temperature coefficient of -0.0004 V/°C. What will be its EMF at 25°C?
Answer: B
EMF at 25°C = 1.0186 - 0.0004 × (25-20) = 1.0186 - 0.002 = 1.0166 ≈ 1.0170 V.
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Q.266Medium
In a LVDT (Linear Variable Differential Transformer), when the core is at null position, what happens to the output voltage?
Answer: B
At null position in LVDT, the core is centered, and secondary voltages from both coils cancel out, resulting in zero or minimum output.
Q.267Medium
In a potentiometer method for EMF comparison, if standard cell EMF is 1.018 V with 106.4 cm length, and unknown cell requires 107.8 cm, what is unknown EMF?
What is the main limitation of analog instruments in automated data acquisition systems?
Answer: B
Analog instruments cannot directly interface with digital computers; they require ADC conversion for data acquisition systems.
Q.269Medium
Which of the following is a sequential logic circuit?
Answer: C
Flip-flops are sequential logic circuits with memory; others are combinational circuits without memory
Q.270Medium
In a JK flip-flop, when J=1 and K=1, the next state will be:
Answer: C
JK flip-flop truth table: J=1, K=1 causes toggle (Q switches to Q', Q' switches to Q)
Q.271Medium
What is the fan-out of a logic gate?
Answer: B
Fan-out specifies how many standard loads (inputs of similar gates) one output can drive without degradation
Q.272Medium
Which digital logic family has the highest speed of operation?
Answer: C
ECL (Emitter Coupled Logic) has propagation delay ~1ns, fastest among families despite higher power consumption
Q.273Medium
The number of logic levels required to represent 32 different states in binary is:
Answer: B
2^n = 32, therefore n = 5 bits (since 2^5 = 32)
Q.274Medium
What is the main advantage of CMOS logic over TTL?
Answer: B
CMOS technology draws power only during switching, resulting in very low static and dynamic power consumption compared to TTL
Q.275Medium
A 4-to-1 multiplexer has inputs A, B, C, D and select lines S₁, S₀. If S₁=0 and S₀=1, which input is selected?
Answer: B
Selection code 01 (binary) = 1 (decimal), which selects input B (second input)
Q.276Medium
In Karnaugh map simplification, a group of 8 adjacent cells eliminates how many variables?
Answer: C
A group of 2^n cells eliminates n variables. Group of 8 = 2^3, eliminates 3 variables
Q.277Medium
What is the primary function of an encoder in digital electronics?
Answer: C
Encoder produces binary-coded output corresponding to only one active input line among many inputs
Q.278Medium
A synchronous counter differs from asynchronous counter in that:
Answer: B
Synchronous counters apply clock to all flip-flops simultaneously, eliminating propagation delay limitations of asynchronous counters
Q.279Medium
In a 4-bit ripple counter, the maximum frequency that can be counted is limited by the:
Answer: A
In ripple counters, each flip-flop must settle before the next one can toggle. The maximum countable frequency is limited by the total propagation delay through all stages.
Q.280Medium
A 3-to-8 decoder with active-low outputs has how many output lines at logic 0 when the input is 101?
Answer: C
A 3-to-8 decoder with active-low outputs means all lines are 1 except the selected one. Input 101 (5 in decimal) selects line 5, so 7 lines remain at 0.
