A step - up transformer is used on 120 V line to provide a potential difference of 2400 V . If the number of turns in the primary is 75, then the number of turns in the secondary shall be

Options

A. 25
B. 150
C. 1500
D. 500

Answer

To find the number of turns in the secondary coil (Ns) of a step-up transformer, we can use the transformer equation which relates the number of turns in the primary (Np) and secondary (Ns) coils to the voltages across them (Vp and Vs). The relationship is given by:

\[ \frac{Ns}{Np} = \frac{Vs}{Vp} \]

### Step-by-Step Solution:

1. **Identify the Given Values:**
- Primary voltage (Vp) = 120 V
- Secondary voltage (Vs) = 2400 V
- Number of turns in the primary (Np) = 75 turns

2. **Set Up the Transformer Equation:**
Using the transformer equation:
\[ \frac{Ns}{Np} = \frac{Vs}{Vp} \]

3. **Substitute the Known Values:**
Substitute the known values into the equation:
\[ \frac{Ns}{75} = \frac{2400}{120} \]

4. **Calculate the Voltage Ratio:**
Simplify the right side:
\[ \frac{2400}{120} = 20 \]
So, the equation becomes:
\[ \frac{Ns}{75} = 20 \]

5. **Solve for Ns:**
Multiply both sides by 75 to isolate Ns:
\[ Ns = 75 \times 20 \]

6. **Perform the Multiplication:**
Calculate the value:
\[ Ns = 1500 \]

### Final Answer:
The number of turns in the secondary coil (Ns) is **1500 turns**.