The arms consisting of the resistances R1 and R2 are called

Option D: Ratio arms Explanation & Concepts: In a Wheatstone bridge circuit, the resistances $R_1$ and $R_2$ form the ratio arms, which determine the sensitivity and multiplication factor of the bridge. The balance condition of the bridge is determined by the ratio of these two arms relative to the other two arms ($R_3$ and $R_x$). Working Principle: The Wheatstone bridge operates on the null-deflection principle. When the bridge is balanced, the potential difference across the galvanometer is zero, leading to the condition $\frac{R_1}{R_2} = \frac{R_3}{R_x}$. By adjusting the ratio $\frac{R_1}{R_2}$, an unknown resistance $R_x$ can be measured precisely. Key Formulas: $\frac{R_1}{R_2} = \frac{R_3}{R_x}$ — Wheatstone bridge balance condition; $R_x = R_3 \cdot (\frac{R_2}{R_1})$ — Expression for unknown resistance Key Points: The ratio arms $R_1$ and $R_2$ are typically fixed or selectable precision resistors.; The bridge sensitivity is optimized when the arms are chosen such that the ratio provides a suitable multiplication factor for the range of $R_x$.; In slide-wire bridges, these arms are segments of a single uniform wire. Advantages: High precision for medium resistance measurements; Eliminates errors due to internal supply variations at null point Disadvantages: Not suitable for extremely low or high resistances; Requires manual or automated balancing Applications: Precision resistance measurement in laboratory environments; Strain gauge measurement circuits; Thermistor-based temperature sensing Additional Info: The term 'Ratio arms' specifically refers to the pair $R_1/R_2$ because their ratio determines the balance point independent of the absolute resistance values.. Option A is incorrect as 'resistance arms' is a generic term for all bridge arms.. Option B is incorrect as 'impedance arms' typically refers to AC bridges (like Maxwell or Hay bridge). Answer: D is correct — The pair of resistors $R_1$ and $R_2$ are known as the ratio arms because their ratio $\frac{R_1}{R_2}$ defines the proportionality of the bridge at balance. Exam Tip: Always remember that in AC bridges (Impedance Bridges), the ratio arms may consist of complex impedances ($Z_1/Z_2$) instead of pure resistances.

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The arms consisting of the resistances R₁ and R₂ are called

Resistance arms

Impedance arms

Source arms

Ratio arms

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Concept & PrincipleElectricalMeasurement & Instrumentation

Option D

Ratio arms

Quick Summary: In a Wheatstone bridge circuit, the resistances $R_1$ and $R_2$ form the ratio arms, which determine the sensitivity and multiplication factor of the bridge. The balance condition of the bridge is determined by the ratio of these two arms relative to the other two arms ($R_3$ and $R_x$).

💡 Explanation

In a Wheatstone bridge circuit, the resistances $R_1$ and $R_2$ form the ratio arms, which determine the sensitivity and multiplication factor of the bridge. The balance condition of the bridge is determined by the ratio of these two arms relative to the other two arms ( $R_3$ and $R_x$ ).

🔢 Key Formulas

$\frac{R_1}{R_2} = \frac{R_3}{R_x}$ — Wheatstone bridge balance condition

$R_x = R_3 \cdot (\frac{R_2}{R_1})$ — Expression for unknown resistance

⚙️ Working Principle

The Wheatstone bridge operates on the null-deflection principle. When the bridge is balanced, the potential difference across the galvanometer is zero, leading to the condition $\frac{R_1}{R_2} = \frac{R_3}{R_x}$ . By adjusting the ratio $\frac{R_1}{R_2}$ , an unknown resistance $R_x$ can be measured precisely.

📌 Key Points

▸
The ratio arms $R_1$ and $R_2$ are typically fixed or selectable precision resistors.
▸
The bridge sensitivity is optimized when the arms are chosen such that the ratio provides a suitable multiplication factor for the range of $R_x$ .
▸
In slide-wire bridges, these arms are segments of a single uniform wire.

✅ Advantages

▸
High precision for medium resistance measurements
▸
Eliminates errors due to internal supply variations at null point

❌ Disadvantages / Limitations

▸
Not suitable for extremely low or high resistances
▸
Requires manual or automated balancing

🛠️ Applications / Uses

▸
Precision resistance measurement in laboratory environments
▸
Strain gauge measurement circuits
▸
Thermistor-based temperature sensing

📄 Additional Information

▸
The term 'Ratio arms' specifically refers to the pair $R_1/R_2$ because their ratio determines the balance point independent of the absolute resistance values.
▸
Option A is incorrect as 'resistance arms' is a generic term for all bridge arms.
▸
Option B is incorrect as 'impedance arms' typically refers to AC bridges (like Maxwell or Hay bridge).

📊 Diagram / Illustration

✅

D is correct — The pair of resistors $R_1$ and $R_2$ are known as the ratio arms because their ratio $\frac{R_1}{R_2}$ defines the proportionality of the bridge at balance.

Core Concepts Used

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Wheatstone Bridge Null Balance Principle Resistance Measurement

💡 EXAM TIP

Always remember that in AC bridges (Impedance Bridges), the ratio arms may consist of complex impedances ( $Z_1/Z_2$ ) instead of pure resistances.

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