Question

A slide potentiometer has 5 wires 2m each. With the help of a standard voltage source of 1.234 V, it is standardized by keeping the jockey at 123.4 cm. If resistance of potentiometer wire is 10000$\Omega$, then the value of working current will be _______.

• A. 1 mA
• B. 0.5 mA
• C. 0.1 mA
• D. 10 mA

Hint:

Use $\frac{L}{L_{total}} = \frac{V_{std}}{IR}$ to find current in potentiometer. Convert lengths and resistances properly.

Answer 1

The Correct Option is D

Step 1: Total wire length
Number of wires = 5, each of 2 m $\Rightarrow$ total length = $5 \times 2 = 10$ m = 1000 cm
Step 2: Balance point at 123.4 cm
At balance point: \[ \frac{\text{Length}}{\text{Total Length}} = \frac{\text{Standard Voltage}}{\text{Total Voltage Drop}} \Rightarrow \frac{123.4}{1000} = \frac{1.234}{IR} \] Step 3: Solve for $I$
Total resistance $R = 10000\,\Omega$, standard voltage = 1.234 V: \[ \frac{123.4}{1000} = \frac{1.234}{I \cdot 10000} \Rightarrow I = \frac{1.234 \cdot 10000}{123.4 \cdot 1000} = \frac{12340}{123400} = 0.1\,\text{A} = \boxed{10\,\text{mA}} \]