Turn ratio of a step-up transformer is 1 : 25. If current in load coil is 2A, then the current in primary coil will be :
(a) 25A (b) 50A (c) 0.25A (d) 0.5A

Options

A. 25A
B. 50A
C. 0.25A
D. 0.5A

Explanation

To solve the problem, we can use the relationship between the turns ratio of a transformer and the currents in the primary and secondary coils.

### Step-by-Step Solution:

1. **Understand the Turns Ratio**:
The turns ratio of a transformer is given as 1:25. This means for every 1 turn in the primary coil, there are 25 turns in the secondary coil.

2. **Identify the Current in the Secondary Coil**:
The current in the load coil (which is the secondary coil) is given as 2 A.

3. **Use the Transformer Current Relationship**:
The relationship between the currents in the primary (I₁) and secondary (I₂) coils of a transformer is given by the formula:
\[ \frac{I₁}{I₂} = \frac{N₁}{N₂} \]
where \(N₁\) is the number of turns in the primary coil and \(N₂\) is the number of turns in the secondary coil.

4. **Substituting the Values**:
From the turns ratio 1:25, we can denote:
\[ N₁ = 1 \quad \text{and} \quad N₂ = 25 \]
Therefore, the relationship becomes:
\[ \frac{I₁}{2} = \frac{1}{25} \]

5. **Cross-Multiply to Solve for I₁**:
Cross-multiplying gives:
\[ I₁ = 2 \times 25 \]

6. **Calculate I₁**:
\[ I₁ = 50 \, \text{A} \]

Thus, the current in the primary coil is **50 A**.

### Final Answer:
(b) 50 A