The length of a potentiometer wire is 10 m and carries steady current on connecting the sliding jockey to standard cell of 1.018 volt, the null point is obtained at the distance of 850 cm.
The maximum e.m.f. that can be measured is:

Options

A. 1.3 volt
B. 1.2 volt
C. 1.4 volt
D. 1.5 volt

Explanation

To solve the problem, we need to determine the maximum electromotive force (e.m.f.) that can be measured using the given potentiometer wire. Here's a step-by-step breakdown of the solution:

### Step 1: Understand the setup
The potentiometer wire has a total length of 10 m (or 1000 cm) and is used to measure the e.m.f. of a standard cell (1.018 V) at a null point obtained at a distance of 850 cm.

### Step 2: Calculate the potential gradient
The potential gradient (k) can be calculated using the formula:
\[ k = \frac{V}{L} \]
where \(V\) is the voltage of the standard cell and \(L\) is the length of the wire up to the null point.

Here, \(V = 1.018 \, \text{V}\) and \(L = 850 \, \text{cm}\).

Substituting the values:
\[ k = \frac{1.018 \, \text{V}}{850 \, \text{cm}} = \frac{1.018}{850} \, \text{V/cm} \]

### Step 3: Calculate the maximum e.m.f.
The maximum e.m.f. (E_max) that can be measured is when the null point is at the end of the wire (10 m or 1000 cm). Thus, we can use the potential gradient to find the maximum e.m.f.:
\[ E_{\text{max}} = k \times \text{Length of the wire} \]
Substituting the values:
\[ E_{\text{max}} = k \times 1000 \, \text{cm} \]
\[ E_{\text{max}} = \left(\frac{1.018}{850}\right) \times 1000 \]

### Step 4: Perform the calculation
Calculating \(E_{\text{max}}\):
\[ E_{\text{max}} = \frac{1.018 \times 1000}{850} \]
\[ E_{\text{max}} = \frac{1018}{850} \approx 1.1976 \, \text{V} \]

### Step 5: Round the result
Rounding this value to two decimal places gives:
\[ E_{\text{max}} \approx 1.20 \, \text{V} \]

### Conclusion
The maximum e.m.f. that can be measured is approximately **1.20 V**.

---