A moving coil galvanometer has a coil resistance of 10 Ω and gives full-scale deflection for 5 mA current. What shunt resistance is required to convert it into an ammeter of range 0-5 A?
Answer: A
Using shunt formula: S = (Ig × Rg) / (I - Ig) = (5×10⁻³ × 10) / (5 - 5×10⁻³) ≈ 0.01 Ω
Q.2Medium
Which bridge circuit is most suitable for measuring an unknown capacitance?
Answer: C
Owen bridge is specifically designed for accurate measurement of unknown inductance and capacitance values in AC circuits.
Q.3Medium
In a Wheat stone bridge, the null deflection is obtained when the ratio of resistances satisfies which condition?
Answer: B
At balance condition in Wheatstone bridge: R₁/R₂ = R₃/R₄, which can be rearranged to R₁ × R₄ = R₂ × R₃
Q.4Medium
A moving iron instrument reads the same for both AC and DC because it:
Answer: A
Moving iron instruments deflect based on the magnitude of current/voltage regardless of direction. The iron core is attracted by the magnetic field produced by the coil in both AC and DC.
Q.5Medium
A thermocouple is used to measure temperature because it:
Answer: D
Thermocouples generate EMF (Seebeck effect) proportional to the temperature difference between junctions and don't require external power.
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Q.6Medium
The mutual inductance between two coils is independent of:
Answer: C
Mutual inductance depends on geometry, coil configuration, and medium properties, but NOT on the current flowing through them.
Q.7Medium
A platinum resistance thermometer (RTD) follows which relationship between resistance and temperature?
Answer: B
RTDs exhibit a nearly linear relationship between resistance and temperature: Rt = R₀(1 + αt + βt²), where the linear term dominates.
Q.8Medium
A Hall effect sensor is primarily used to measure:
Answer: B
Hall effect sensors detect the magnetic field strength by measuring the Hall voltage generated when a current-carrying conductor is placed in a perpendicular magnetic field.
Q.9Medium
The power factor of a circuit can be improved by adding:
Answer: C
Power factor (lagging) is improved by adding shunt capacitance, which creates a leading current that offsets the lagging component.
Q.10Medium
The null deflection method in bridge circuits is preferred over deflection method because it:
Answer: B
Null deflection (or balance) method is preferred because it doesn't depend on meter calibration or linearity. The measurement relies on the balance condition formula only.
Q.11Medium
A moving coil galvanometer has an internal resistance of 10 Ω and a full-scale deflection current of 5 mA. What shunt resistance is required to convert it into an ammeter with a range of 0-5 A?
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.13Medium
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.14Medium
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.15Medium
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.16Medium
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.
Q.17Medium
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.18Medium
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?
