The correct option for measuring a cell with an internal resistance of 0.01Ω is **C. potentiometer**. ### Detailed Explanation 1. **Understanding Internal Resistance**: - Every cell or battery has an internal resistance, which is the resistance to the flow of current within the cell itself. This internal resistance can affect the performance of the cell when it is connected to a circuit. To measure this resistance accurately, we need a method that minimizes the impact of the cell's own voltage and current. 2. **Why a Potentiometer?**: - A potentiometer is an instrument used to measure the potential difference (voltage) across a component in a circuit without drawing any current from the circuit. This is crucial when measuring internal resistance because drawing current would change the voltage across the cell, leading to inaccurate readings. - The potentiometer works on the principle of balancing the voltage across a known resistance with the voltage across the unknown resistance (in this case, the internal resistance of the cell). By adjusting the potentiometer until the voltages are equal, you can determine the internal resistance accurately. 3. **How to Use a Potentiometer**: - Connect the potentiometer in a circuit with the cell whose internal resistance you want to measure. - Adjust the sliding contact of the potentiometer until the galvanometer (a sensitive current measuring device) shows zero deflection, indicating that the voltage across the potentiometer wire is equal to the voltage across the internal resistance of the cell. - From the known values of the potentiometer and the current flowing through the circuit, you can calculate the internal resistance using Ohm's law and the formula for resistors in series. ### Why the Other Options Are Incorrect: - **A. Ohm Meter**: - An ohm meter measures resistance by passing a current through the resistor and measuring the voltage drop across it. However, this method would draw current from the cell, which would affect the voltage and lead to an inaccurate measurement of the internal resistance. Therefore, it is not suitable for measuring the internal resistance of a cell. - **B. Metre Bridge**: - A metre bridge is a device used to measure unknown resistances by balancing them against known resistances. While it can measure resistance accurately, it also requires current to flow through the circuit, which would again affect the measurement of the internal resistance of the cell. Thus, it is not ideal for this purpose. - **D. Electroscope**: - An electroscope is an instrument used to detect electric charge, not to measure resistance. It does not provide any means to measure internal resistance and is therefore irrelevant in this context. ### Summary of Key Points: - The potentiometer is the best choice for measuring internal resistance because it does not draw current from the cell, ensuring accurate readings. - Other methods like the ohm meter and metre bridge are unsuitable as they alter the voltage across the cell by drawing current. - An electroscope is not designed for measuring resistance at all. ### Revision Summary: - **Potentiometer**: Ideal for measuring internal resistance without drawing current. - **Ohm Meter**: Draws current, leading to inaccurate measurements. - **Metre Bridge**: Requires current flow, affecting voltage readings. - **Electroscope**: Not applicable for resistance measurement.