Standard Operating Procedure (SOP)

Here’s a Standard Operating Procedure (SOP) for the Operation of a Potentiometer – commonly used in laboratories for electrical measurements, especially to measure electromotive force (EMF), potential difference, and internal resistance of cells.

1. Purpose

To provide a standardized procedure for the correct and safe operation of a Potentiometer to ensure accurate and reliable measurement of voltage and other related electrical parameters.

2. Scope

This SOP is applicable to all laboratory personnel operating the potentiometer in [Company/Institute Name], for academic, testing, or calibration purposes.

3. Responsibilities

• Laboratory Personnel:

  • Operate the potentiometer as per this SOP.

  • Report any malfunction or irregularities.

• Lab In-charge/Supervisor:

  • Ensure training and compliance with this SOP.

  • Schedule maintenance and calibration.

4. Definitions

• Potentiometer: A device used to measure unknown voltage by balancing it against a known voltage in a circuit.

• Galvanometer: A sensitive instrument used to detect null conditions in the potentiometer circuit.

5. Materials and Equipment Required

• Potentiometer setup

• Galvanometer

• Standard cell (e.g., Daniel cell)

• Leclanché cell or unknown voltage source

• Rheostat

• Connecting wires

• Key/switch

• Power supply or battery

• Jockey (sliding contact)

6. Procedure

6.1 Safety Precautions

• Ensure all connections are secure before switching on power.

• Use low voltage DC supply to avoid damage.

• Avoid short circuits – check wire insulation and connections.

• Handle all components with dry hands.

6.2 Setup and Calibration

1. Check the Potentiometer Wire:

   • Ensure the potentiometer wire is uniform and untarnished.

2. Connect the Circuit:

   • Connect one end of the potentiometer wire to a battery or power source through a key (K1) and rheostat (for current adjustment).

   • Connect a standard cell (like a Daniel cell) and galvanometer in the secondary circuit with another key (K2).

3. Adjust the Current:

   • Close K1 and adjust the rheostat so that the current through the potentiometer wire is steady (checked using a voltmeter if needed).

6.3 Measurement of Unknown EMF

1. Calibration (Using Standard Cell):

   • Close K2 and slide the jockey along the potentiometer wire.

   • Find the null point where the galvanometer shows zero deflection.

   • Note the balancing length (L₁).

   • Calculate the potential drop per unit length (K) using:

     K=EstandardL1K = \frac{E_{standard}}{L_1}K=L1​Estandard​​

2. Measuring Unknown Voltage:

   • Replace the standard cell with the unknown EMF source.

   • Repeat the null point search.

   • Note the new balancing length (L₂).

   • Calculate the unknown EMF (Eₓ) using:

     Ex=K×L2E_x = K \times L_2Ex​=K×L2​

6.4 Measurement of Internal Resistance (Optional)

1. Connect the cell with and without external resistance (e.g., a known resistor).

2. Measure the balancing lengths in both cases.

3. Calculate internal resistance using the formula:

   r=R(L1−L2L2)r = R \left( \frac{L_1 – L_2}{L_2} \right)r=R(L2​L1​−L2​​)

   where R is the known external resistance, L₁ and L₂ are balancing lengths without and with R.

7. Post-Operation Procedure

• Switch off power and disconnect the setup.

• Clean the potentiometer wire and ensure it is free from dust or oxidation.

• Store all equipment properly.

• Record readings and observations in the lab register.

8. Documentation

Maintain a log of:

• Date and time of operation

• Operator name

• Calibration details

• Voltage measurements

• Any anomalies or maintenance notes

9. References

• Physics Laboratory Manual

• Equipment Manufacturer’s Manual

• BIS/ISO standards for electrical measurement (if applicable)

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