Which of the following statements is false?

Options

A. A rheostat can be used as a potential divider
B. Kirchhoff's second law represents energy conservation
C. Wheatstone bridge is the most sensitive when all the four resistances are of the same order of magnitude
D. In a balanced Wheatstone bridge if the cell and the galvanometer are exchanged, the null point is disturbed.

Answer

To determine which statement is false among the given options, we will analyze each statement one by one.

### Step 1: Analyze the first statement
**Statement 1:** A rheostat can be used as a potentiometer.

- A rheostat is a variable resistor that can adjust current in a circuit.
- A potentiometer is a device that measures voltage by balancing two sides of a circuit.
- While a rheostat can be used to vary resistance and indirectly measure voltage, it does not function as a potentiometer in the traditional sense where it provides a constant voltage reference.

**Conclusion:** This statement is misleading and can be considered false.

### Step 2: Analyze the second statement
**Statement 2:** Kirchhoff's second law represents energy conservation.

- Kirchhoff's second law states that the sum of the potential differences (voltage) around any closed loop in a circuit must equal zero.
- This law is based on the principle of conservation of energy, as it implies that energy supplied is equal to energy used.

**Conclusion:** This statement is true.

### Step 3: Analyze the third statement
**Statement 3:** The Wheatstone bridge is the most sensitive when all four resistances are of the same order and of the same magnitude.

- The Wheatstone bridge is used to measure unknown resistances.
- It achieves maximum sensitivity when the ratios of the resistances are equal (i.e., when all resistances are of the same magnitude).
- This condition ensures that the galvanometer shows zero deflection, indicating a balanced state.

**Conclusion:** This statement is true.

### Step 4: Analyze the fourth statement
**Statement 4:** If the cell and galvanometer in a Wheatstone bridge are exchanged, the null point is disturbed.

- In a Wheatstone bridge, exchanging the cell and galvanometer does not disturb the balance of the bridge.
- The ratios of the resistances remain the same, and thus the condition for balance is still satisfied.

**Conclusion:** This statement is false.

### Final Conclusion
The false statements identified are:
1. A rheostat can be used as a potentiometer (misleading).
2. If the cell and galvanometer in a Wheatstone bridge are exchanged, the null point is disturbed (incorrect).

### Summary
The false statement among the options is: "A rheostat can be used as a potentiometer."

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