please give the answer of (iii) no.....I have also another question ….”Comparison of Ammeter voltmeter method and kelvins double bridge method using their advantages and disadvantages

When comparing the Ammeter-Voltmeter method and the Kelvin's Double Bridge method for measuring electrical resistance, it's essential to understand the context in which each method is used, as well as their respective advantages and disadvantages. Both methods serve the purpose of measuring resistance, but they do so in different ways and are suited for different applications.

Ammeter-Voltmeter Method

The Ammeter-Voltmeter method involves using an ammeter to measure the current flowing through a resistor and a voltmeter to measure the voltage across that resistor. The resistance can then be calculated using Ohm's Law, which states that R = V/I, where R is resistance, V is voltage, and I is current.

Advantages

• Simplicity: This method is straightforward and easy to set up, making it accessible for basic experiments and educational purposes.
• Cost-effective: Ammeter and voltmeter are commonly available and relatively inexpensive compared to more specialized equipment.
• Quick Measurements: It allows for rapid measurements, which is beneficial in situations where time is a factor.

Disadvantages

• Measurement Errors: The method can introduce significant errors, especially if the internal resistance of the measuring instruments is not negligible compared to the resistance being measured.
• Limited Accuracy: It is less accurate for low resistance values due to the potential impact of contact and lead resistances.
• Power Dissipation: The method can lead to power dissipation in the resistor being measured, which can affect the measurement if the resistor heats up.

Kelvin's Double Bridge Method

Kelvin's Double Bridge method, also known as the four-wire method, is designed specifically for measuring low resistances with high accuracy. It uses four leads: two for supplying current and two for measuring voltage. This configuration minimizes the effect of lead and contact resistances on the measurement.

Advantages

• High Precision: This method provides very accurate measurements, making it ideal for low-resistance applications, such as in the calibration of standards.
• Minimized Errors: By separating the current-carrying leads from the voltage-measuring leads, it effectively eliminates errors due to lead resistance.
• Suitable for Low Resistances: It excels in measuring resistances that are very low, where other methods might fail to provide reliable results.

Disadvantages

• Complex Setup: The setup is more complicated than the Ammeter-Voltmeter method, requiring careful arrangement and calibration.
• Higher Cost: The equipment needed for this method is generally more expensive and may not be readily available in all laboratories.
• Time-Consuming: The process can take longer due to the need for careful adjustments and calibrations.

Summary of Comparison

In summary, the choice between the Ammeter-Voltmeter method and Kelvin's Double Bridge method largely depends on the specific requirements of the measurement task at hand. For quick, general-purpose resistance measurements, the Ammeter-Voltmeter method is often sufficient. However, for applications requiring high precision, particularly in low-resistance scenarios, the Kelvin's Double Bridge method is the preferred choice due to its accuracy and ability to minimize measurement errors.

Understanding these methods and their respective advantages and disadvantages can help you select the appropriate technique for your specific needs in electrical measurements.