Kelvins Bridge Experiment Questions and Answers for Viva

Answer-1: The primary objective of Kelvin's Double Bridge Experiment is to measure the electrical resistance of an unknown resistor precisely by comparing it to known standard resistors and using the principles of electrical bridge circuits.

Answer-2: A Kelvin's Double Bridge setup typically includes the following components:
A bridge circuit with four arms, consisting of resistors and the unknown resistor.
A galvanometer or null detector to measure balance in the bridge.
A calibrated dial or rheostat for adjusting one or more resistances.
A known standard resistor or set of standard resistors.

Answer-3: Kelvin's Double Bridge works on the principle of Wheatstone's Bridge, with the addition of a ratio arm. By adjusting the values of the resistors in the arms of the bridge, you create a balanced condition where no current flows through the galvanometer. At this point, the ratio of known resistors to the unknown resistor is used to calculate the value of the unknown resistance.

Answer-4: Nulling the galvanometer is essential because it indicates a balanced condition in the bridge circuit. In this balanced state, no current flows through the galvanometer, and the ratio of resistances is accurate for calculating the unknown resistance. Nulling ensures precision in the measurement.

Answer-5: Several factors can affect the accuracy of the experiment, including:
Resistance temperature coefficients.
Variations in temperature during the experiment.
Imperfections in the standard resistors.
Nonlinearity in the galvanometer or null detector.
Electrical noise in the circuit.
Poor electrical connections.

Answer-6: To improve the accuracy of the experiment, you can:
Use high-quality and stable standard resistors.
Maintain a constant and controlled temperature.
Shield the circuit from external electrical noise.
Ensure clean and tight electrical connections.
Carefully null the galvanometer.
Conduct multiple measurements and calculate an average.

Answer-7: The key difference is that the Kelvin Double Bridge is used for measuring low resistances, whereas the Wheatstone Bridge is primarily used for measuring unknown resistances in the medium to high range. In the Kelvin Bridge, a fourth arm with known low resistance is added to the Wheatstone Bridge, making it suitable for low resistance measurements.

Answer-8: It is called the "double bridge" method because it combines two bridge circuits: the Wheatstone Bridge and the Kelvin Bridge. The addition of the fourth arm with a low known resistance creates a double bridge configuration.

Answer-9: Yes, Kelvin's Double Bridge is specifically designed for the measurement of low resistance values. It is highly beneficial for accurately measuring resistances in the low range.

Answer-10: Some limitations include the need for precise calibration, the potential for errors due to temperature variations, and the requirement for stable power sources.

Answer-11: Kelvin's Double Bridge is most effective for measuring resistances in the range of milliohms (10^-3 ohms) to a few ohms.

Answer-12: Low resistance: Typically, milliohms (10^-3 ohms) to ohms.
Medium resistance: Ohms to kilohms (10³ ohms).
High resistance: Kilohms (10³ ohms) and above.

Answer-13:
Advantages:
Highly accurate for low resistance measurements.
Precise calibration and low measurement uncertainty.
Eliminates errors due to lead resistance.
Disadvantages:
Limited to low resistance measurements.
Sensitive to environmental factors like temperature changes.
Requires careful handling and calibration.

Answer-14:
Kelvin's Double Bridge is commonly used in applications that require precise measurement of low resistances, such as:Calibration of resistance standards.
Measurement of contact resistances in electrical circuits.
Testing of electrical connections and joints.
Quality control in electronics manufacturing.

Answer-15: The errors in Kelvin's Bridge can arise from various sources, including:
Temperature variations affecting resistance values.
Imperfections in the standard resistors.
Electrical noise and interference.
Non-ideal characteristics of components like switches and connectors.
Calibration errors in the bridge components.