Which of the following quantity remains constant in an ideal transformer ?

Options

A. Current
B. Voltage
C. Power
D. All of these

Explanation

To solve the question "Which of the following quantity remains constant in an ideal transformer?" we will analyze the properties of an ideal transformer step by step.

### Step-by-Step Solution:

1. **Understanding the Concept of an Ideal Transformer**:
An ideal transformer is a device that transfers electrical energy between two or more circuits through electromagnetic induction. It operates under the principle of conservation of energy.

2. **Efficiency of an Ideal Transformer**:
The efficiency (η) of an ideal transformer is defined as:
\[ \eta = \frac{\text{Power Output}}{\text{Power Input}} \]
For an ideal transformer, this efficiency is equal to 1 (or 100%).

3. **Power Input and Power Output**:
Since the efficiency is 1, we can conclude that:
\[ \text{Power Output} = \text{Power Input} \]
This means that the power remains constant in an ideal transformer.

4. **Analyzing Other Quantities**:
- **Voltage**: In an ideal transformer, the voltage can change based on the turns ratio of the primary and secondary coils. Therefore, voltage is not constant.
- **Current**: Similarly, the current can also change depending on the load connected to the transformer and the turns ratio. Hence, current is not constant.

5. **Conclusion**:
From the analysis, we can conclude that the only quantity that remains constant in an ideal transformer is the power. Therefore, the correct answer is:
\[ \text{Power} \]

### Final Answer:
The quantity that remains constant in an ideal transformer is **Power**.

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