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.502Medium
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.503Easy
The class of accuracy for a class 1.5 instrument means:
Answer: C
The accuracy class (e.g., 1.5, 2.0) indicates the maximum percentage error with respect to full scale deflection, as per IEC standards.
Q.504Medium
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.
Q.505Hard
For accurate power measurement in a three-phase system with unbalanced load, the minimum number of wattmeters required is:
Answer: C
For unbalanced three-phase loads, three wattmeters are required—one in each phase—to measure total power accurately.
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Q.506Medium
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.507Medium
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.508Easy
The input impedance of a digital multimeter is typically:
Answer: C
Modern digital multimeters have very high input impedance (typically 10 MΩ for voltage measurement) to minimize loading effects on the circuit.
Q.509Easy
In a CRO (Cathode Ray Oscilloscope), the Y-deflection sensitivity is expressed in:
Answer: A
Y-deflection sensitivity (or gain) in CRO is expressed in volts per division, indicating how many volts are represented by each vertical division.
Q.510Medium
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.511Medium
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.512Easy
The sensitivity of a galvanometer is defined as:
Answer: A
Sensitivity of a galvanometer is the deflection (in mm or degrees) produced per unit current (usually per microampere or milliampere).
Q.513Hard
In an AC bridge at balance condition, if R₁ = 100 Ω, R₂ = 50 Ω, and R₃ (inductive) = 200 Ω with series R, then R₄ is:
Answer: A
Using AC bridge balance: Z₁/Z₂ = Z₃/Z₄; therefore 50100 = 200/Z₄, which gives Z₄ = 100 Ω
Q.514Medium
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.515Medium
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?
Which of the following is NOT a source of error in analog voltmeters?
Answer: C
Analog voltmeters are primarily DC devices. Frequency changes affect AC measurements but not the instrument's basic construction errors.
Q.517Hard
In a Kelvin's double bridge used for measuring low resistances (< 0.1 Ω), which configuration is adopted?
Answer: B
Kelvin's double bridge uses cross-connection to eliminate lead resistance errors when measuring very low resistances in industrial applications.
Q.518Easy
A thermocouple generates 50 μV for a temperature difference of 1°C between its junctions. What is its sensitivity?
Answer: A
Sensitivity is the ratio of output to input. Here, sensitivity = 50 μV/1°C = 50 μV/°C.
Q.519Medium
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.520Easy
In a CRO probe with 10:1 attenuation ratio, if the actual voltage is 100 V, what voltage appears across the CRO input terminals?
Answer: A
With 10:1 attenuation, the voltage at CRO terminals = Actual voltage/10 = 10100 = 10 V.
