Assertion : A step-up transformer changes a low voltage into a high voltage.
Reason : This violate the law of conservation of energy.

Options

A. If both assertion ans reason are true ans reaason is the correct explanation of assertion.
B. If both assertion and reason are true but reason is not the correct explanation of assertion.
C. If assertion istrue but reason is false.
D. If both assertion and reason are false.

Explanation

To solve the question, we need to analyze both the assertion and the reason provided.

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that "A step-up transformer changes a low voltage into a high voltage."
- This is true. A step-up transformer is designed to increase the voltage from the primary coil to the secondary coil.

2. **Understanding the Reason**:
- The reason states that "This violates the law of conservation of energy."
- This statement is false. A step-up transformer does not violate the law of conservation of energy. While it increases voltage, it decreases current proportionally, ensuring that the power (which is the product of voltage and current) remains constant (ignoring losses).

3. **Analyzing the Relationship**:
- In a transformer, the power input (P1 = V1 * I1) is equal to the power output (P2 = V2 * I2) under ideal conditions (ignoring losses).
- For a step-up transformer, if the voltage increases (V2 > V1), the current must decrease (I2 < I1) to maintain power balance: V1 * I1 = V2 * I2.

4. **Conclusion**:
- The assertion is true, while the reason is false. Thus, the correct answer is that the assertion is true, but the reason is false.

### Final Answer:
- Assertion is true, Reason is false. Therefore, the correct option is C.