It seems like you want to know about the potentiometer in the context of 12th class physics for various boards in Pakistan. Here's a step-by-step explanation:

1. Introduction: A potentiometer is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider. It is used to measure the electromotive force (emf) of a given cell, compare the emf of different cells, and as a variable resistance in electric circuits.

2. Construction: A potentiometer consists of a long wire of uniform cross-sectional area and of 10 ohms resistance. It is usually made of manganese or constantan. The wire is wound uniformly on a wooden or metal frame. The length of the wire is usually 4-10 meters.

3. Working Principle: The working principle of a potentiometer is based on the fact that the potential drop across any length of a wire of uniform cross-section carrying a constant current is directly proportional to its length.

4. Use in Circuit: In a circuit, the potentiometer is connected in series with a battery (known as driver cell) and a rheostat. The rheostat is used to adjust the current flowing through the circuit. The cell (whose emf is to be measured) is connected in parallel to a part of the potentiometer wire.

5. Measurement: The jockey is slid along the wire until a point is found where the galvanometer shows zero deflection. This indicates that the potential difference across the selected length of the wire is equal to the emf of the cell. The emf of the cell can then be calculated using the formula E = KL, where K is the potential gradient and L is the balancing length.

6. Advantages: The main advantage of a potentiometer is that it can measure emf without drawing any current from the cell. This makes it a very accurate device for measuring and comparing emf.

7. Disadvantages: The main disadvantage is that it can only measure emf up to the emf of the driver cell. If the emf of the cell under test is higher than the driver cell, the potentiometer will not give a correct reading.

This is a basic overview of the potentiometer as taught in class 12 physics. The exact details might vary slightly depending on the specific board (KPK, Federal, Punjab, Sindh, Balochistan).

Question

It seems like you want to know about the potentiometer in the context of 12th class physics for various boards in Pakistan. Here's a step-by-step explanation:

1. Introduction: A potentiometer is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider. It is used to measure the electromotive force (emf) of a given cell, compare the emf of different cells, and as a variable resistance in electric circuits.

2. Construction: A potentiometer consists of a long wire of uniform cross-sectional area and of 10 ohms resistance. It is usually made of manganese or constantan. The wire is wound uniformly on a wooden or metal frame. The length of the wire is usually 4-10 meters.

3. Working Principle: The working principle of a potentiometer is based on the fact that the potential drop across any length of a wire of uniform cross-section carrying a constant current is directly proportional to its length.

4. Use in Circuit: In a circuit, the potentiometer is connected in series with a battery (known as driver cell) and a rheostat. The rheostat is used to adjust the current flowing through the circuit. The cell (whose emf is to be measured) is connected in parallel to a part of the potentiometer wire.

5. Measurement: The jockey is slid along the wire until a point is found where the galvanometer shows zero deflection. This indicates that the potential difference across the selected length of the wire is equal to the emf of the cell. The emf of the cell can then be calculated using the formula E = KL, where K is the potential gradient and L is the balancing length.

6. Advantages: The main advantage of a potentiometer is that it can measure emf without drawing any current from the cell. This makes it a very accurate device for measuring and comparing emf.

7. Disadvantages: The main disadvantage is that it can only measure emf up to the emf of the driver cell. If the emf of the cell under test is higher than the driver cell, the potentiometer will not give a correct reading.

This is a basic overview of the potentiometer as taught in class 12 physics. The exact details might vary slightly depending on the specific board (KPK, Federal, Punjab, Sindh, Balochistan).

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