Physics Experiment: Internal Resistance of a Cell

A device for measuring potential difference and electromotive force.

The resistance encountered by current flow within a cell.

A circuit where voltage is divided among resistors.

The voltage supplied by a cell or battery.

Materials with low temperature resistance change (e.g., Manganin or Constantan).

The total resistance of the galvanometer and the internal resistance of the cell (E1).

The total current entering a junction equals the total current leaving that junction.

The voltage difference across the resistance (Ro) created by the current IG.

Voltage difference across the cell (E1).

The voltage difference between points A and J. This is determined by the combined effect of voltage drops and the cell voltage (E1).

The current flowing through the combined resistance (Ro).

The direction of current (IG) through the combined resistance (Ro) changes based on the connection polarities of the cells (E & E1).

IG = [E - E1] / Ro. The current (IG) depends on the voltages (E and E1) and the total resistance (Ro).

The direction of the current through the galvanometer (IG) depends on the position of the sliding contact (J) on the wire. If IG is positive, the pointer deflects in one direction. If IG is negative, it deflects in the opposite direction.

The null point is the position of the sliding contact (J) where no current flows through the galvanometer (IG = 0).

The null point's position depends on the value of the rheostat (Rh). Adjusting Rh changes the balance of currents, shifting the null point.

The polarities of the electrodes connected to junction 'A' must be the same (either both positive or both negative). This ensures the current can flow in both directions.

The value of 'l' (distance between 'A' and 'J') affects the current through the galvanometer (IG). Changing 'l' alters the potential difference across the galvanometer circuit, leading to different current values.

The rheostat's resistance (Rh) affects the magnitude of current (IG). A lower Rh leads to a higher IG, potentially making it positive and causing deflection in one direction. A higher Rh can decrease IG, potentially making it negative and causing deflection in the other direction.

The maximum value of the rheostat (Rh) below which the galvanometer's pointer can deflect in both directions. This value is determined by the EMF of the cells and the length of the potentiometer wire.

The formula for the cut-off value is Rh < (E - E1) / E1 * R, where E and E1 are the EMFs of the cells, and R is the resistance of the potentiometer wire.

The potentiometer's wire acts as the conductor AB, allowing for precise measurement of potential differences along its length.

Key K connects the resistance box (R) to the cell's negative terminal, allowing current to flow through R and the cell's internal resistance (r) when closed.

Key K1 ensures a continuous path for current to flow through the potentiometer's wire, enabling the detection of null points.

The null point indicates where the potential difference between the potentiometer wire and the cell's internal resistance is zero, allowing for accurate measurement of the internal resistance.

Internal resistance (r) is determined by comparing the lengths of potentiometer wire at different null points, using the formula: r = ((l2/l1) - 1) * R.

Keeping K1 open prevents current flow through the potentiometer's wire, ensuring the wire's resistance remains constant and accurate readings are obtained.

The voltmeter measures the voltage across the cell (V1) when unconnected and then again (V2) when connected to a resistor, allowing calculation of the internal resistance.

Internal resistance (r) is calculated using the formula: r = ((V1/V2) - 1) * R, where V1 is the open-circuit voltage, V2 is the voltage under load, and R is the external resistance.

The ratio of two voltages (E1 and E2) is equal to the ratio of their corresponding lengths (l1 and l2) on the potentiometer wire: E1/E2 = l1/l2.

Connect the cell across the potentiometer wire and find the null point. The length of the wire between the end and the null point (l1) gives the EMF (E1) using the equation: E1 = (l1 / (L + Rh/σ)).

A real cell has both an electromotive force (EMF) and an internal resistance (r).

The cell's EMF is divided between the external resistance (R) and its internal resistance (r) when a current (I) flows through the circuit.

The current through the combined resistance (Ro) is determined by the difference between the EMF of the external circuit (E) and the cell's EMF (E1) divided by the combined resistance: IG = (E - E1) / Ro.

The direction of the current (IG) through Ro depends on the polarity connections of the cells (E and E1).

A potentiometer is used to precisely compare and measure electromotive forces or potential differences by finding the null point, where the current through the galvanometer is zero, thereby indicating equal voltage drops.

Potentiometer wires are made of materials like Manganin or Constantan because these alloys have a very low temperature coefficient of resistance, meaning their resistance remains relatively constant despite temperature changes, ensuring accurate measurements.

The resistance a battery or cell offers to the flow of current within itself.

The potential difference across a resistor is determined by the current flowing through it and the value of the resistor itself, following Ohm's Law: V=IR.

A potentiometer measures voltage by comparing an unknown voltage with a known voltage source. The unknown voltage is compared to a known reference voltage from a battery. By adjusting the sliding contact on the potentiometer wire, a balance point is reached where no current flows through the galvanometer. This point represents the unknown voltage.

The galvanometer in a potentiometer acts as a null detector. It indicates when the potential difference between the two points being compared is zero. This is crucial for determining the balance point in the circuit.

The distance from the end of the potentiometer wire to the null point is directly proportional to the potential difference being measured. This means that a longer distance indicates a higher voltage and vice versa.

The resistance box in a potentiometer allows you to adjust the current flowing through the circuit. This is important for controlling the potential difference across the potentiometer wire and achieving a balance point.

You can calculate the internal resistance of a cell using the potentiometer by setting up a circuit with a known voltage source, the cell, a resistance box, and the potentiometer wire. The internal resistance is calculated from the balance point distances corresponding to different values of the resistance box.