The ratio of secondary to primary turns is 4:5. if power input is P, then the ratio of power output to power input is

Options

A. `4:9`
B. `9:4`
C. `5:4`
D. `1:1`

Explanation

To solve the problem, we need to understand the relationship between the primary and secondary turns of a transformer and how it affects the power output in relation to the power input.

### Step-by-Step Solution:

1. **Identify the Given Ratio of Turns**:
The ratio of secondary turns (Ns) to primary turns (Np) is given as:
\[ \frac{Ns}{Np} = \frac{4}{5} \]

2. **Understand the Power Relationship in an Ideal Transformer**:
In an ideal transformer, the power input (P_in) is equal to the power output (P_out). This can be expressed as:
\[ P_{in} = P_{out} \]

3. **Express the Power Output in Terms of Power Input**:
Since we are assuming an ideal transformer, we can write:
\[ \frac{P_{out}}{P_{in}} = 1 \]

4. **Conclusion**:
Therefore, the ratio of power output to power input is:
\[ \frac{P_{out}}{P_{in}} = 1 \]

### Final Answer:
The ratio of power output to power input is 1:1.