Question

Why is the Wheatstone bridge better than the other methods of measuring resistances?

• A. It is based on Kirchoff’s law
• B. It does not involve Ohm’s law
• C. It has four resistor arms
• D. It is a null method

Answer 1

The Correct Option is D

We need to explain why the Wheatstone bridge method is considered better than other methods for measuring resistances.

1. Understanding the Wheatstone Bridge:
The Wheatstone bridge is a circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit. It consists of four resistors, a voltage source, and a galvanometer. The unknown resistance is determined when the bridge is balanced (no current flows through the galvanometer).

2. High Accuracy and Precision:
The Wheatstone bridge offers high accuracy because it operates on a null method, meaning it measures the unknown resistance by achieving a balance condition where no current flows through the galvanometer. This eliminates errors due to the galvanometer's sensitivity or calibration, making the measurement independent of the voltage source's exact value.

3. Comparison with Other Methods:
- Voltmeter-Ammeter Method: This method measures voltage and current across the resistor to calculate resistance using Ohm’s law (\( R = \frac{V}{I} \)). However, the voltmeter and ammeter have internal resistances, introducing errors, especially for very low or very high resistances.
- Ohmmeter Method: An ohmmeter directly measures resistance but is less accurate for precise measurements due to calibration issues and the influence of the meter’s internal resistance.
The Wheatstone bridge avoids these issues by not relying on direct current or voltage measurements across the unknown resistor.

4. Insensitivity to External Factors:
The Wheatstone bridge is less affected by variations in the power supply voltage or temperature changes, as the balance condition depends only on the ratio of resistances in the bridge arms, not their absolute values.

5. Wide Range and Versatility:
The Wheatstone bridge can measure a wide range of resistances (from very low to very high) with high precision by adjusting the known resistors in the bridge, making it more versatile than methods like the voltmeter-ammeter method, which struggle with extreme resistance values.

Final Answer:
The Wheatstone bridge is better than other methods of measuring resistances because it provides higher accuracy through its null measurement technique, is less affected by external factors like power supply variations, and can measure a wide range of resistances with precision.