Question

Low resistance is measured by

• A. De-Sauty's bridge
• B. Maxwell's bridge
• C. Kelvin's double bridge
• D. Wein's bridge

Hint:

Remember the bridge applications:
1. Kelvin's Double Bridge $\rightarrow$ Low Resistance.
2. Wheatstone Bridge $\rightarrow$ Medium Resistance.
3. Megger Loss of Charge Method $\rightarrow$ High Resistance.
4. Maxwell Hay Anderson $\rightarrow$ Inductance.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks to identify which of the given electrical bridges is designed and used specifically for measuring low resistances.

Step 2: Detailed Explanation:

• Electrical resistances are broadly classified into three categories based on their values:
- Low resistance: Less than or equal to \( 1\ \Omega \).
- Medium resistance: From \( 1\ \Omega \) to \( 100\text{ k}\Omega \).
- High resistance: Greater than \( 100\text{ k}\Omega \).

• Measurement of low resistance requires special care because lead resistances and contact resistances can introduce significant relative errors.

• Kelvin's double bridge is a modification of the traditional Wheatstone bridge. It incorporates a second set of ratio arms to eliminate the effect of contact and lead resistances, ensuring highly accurate measurements of low resistances.

• Let us analyze the other options:
- De-Sauty's bridge is used to measure pure capacitance.
- Maxwell's bridge is used to measure medium inductance.
- Wein's bridge is primarily used to measure frequency and capacitance.

• Therefore, Kelvin's double bridge is the unique correct option for low resistance measurement.