A transformer has 50 turns in the primary and 100 in the secondary. If the primary is connected to a `220 V DC` supply, what will be the voltage across the secondary?

Explanation

To solve the problem, we need to understand the functioning of a transformer and the implications of connecting it to a DC supply.

### Step-by-Step Solution:

1. **Understanding the Transformer**: A transformer operates on the principle of electromagnetic induction, which requires a changing magnetic field to induce voltage in the secondary coil. This changing magnetic field is produced by an alternating current (AC).

2. **Primary and Secondary Turns**: The transformer in question has 50 turns in the primary coil and 100 turns in the secondary coil. The turns ratio (N) can be calculated as follows:
\[ N = \frac{N_s}{N_p} = \frac{100}{50} = 2 \]
This means that the secondary voltage (V_s) would be twice the primary voltage (V_p) if it were connected to an AC supply.

3. **Connection to DC Supply**: The problem states that the primary is connected to a 220 V DC supply. It is crucial to note that transformers do not function with DC voltage. When a DC voltage is applied to the primary coil, there is no changing magnetic field produced.

4. **Voltage Across the Secondary**: Since the transformer does not work with DC, the voltage induced in the secondary coil (V_s) will be:
\[ V_s = 0 \, \text{V} \]

5. **Conclusion**: Therefore, the voltage across the secondary when the primary is connected to a 220 V DC supply is 0 V.

### Final Answer:
The voltage across the secondary is **0 V**.

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