The primary and secondary voltage of an ideal step down transformer are 200 V and 25V respectively. The secondary is connected to a device, which draws a current of 2A. What is the current in the primary?

Options

A. 100 mA
B. 150 mA
C. 200 mA
D. 250 mA

Explanation

To find the current in the primary coil of an ideal step-down transformer, we can use the relationship between the primary and secondary voltages and currents. Here’s a step-by-step solution:

### Step 1: Write down the given values
- Primary Voltage (Vp) = 200 V
- Secondary Voltage (Vs) = 25 V
- Secondary Current (Is) = 2 A

### Step 2: Use the transformer equation
For an ideal transformer, the relationship between the primary and secondary voltages and currents is given by the formula:

\[ \frac{V_s}{V_p} = \frac{I_p}{I_s} \]

Where:
- \( V_s \) = Secondary Voltage
- \( V_p \) = Primary Voltage
- \( I_s \) = Secondary Current
- \( I_p \) = Primary Current

### Step 3: Rearrange the formula to find the primary current (Ip)
We can rearrange the formula to solve for \( I_p \):

\[ I_p = I_s \times \frac{V_s}{V_p} \]

### Step 4: Substitute the known values into the equation
Now, substitute the known values into the equation:

\[ I_p = 2 \, \text{A} \times \frac{25 \, \text{V}}{200 \, \text{V}} \]

### Step 5: Calculate the primary current
Now, perform the calculation:

\[ I_p = 2 \, \text{A} \times \frac{25}{200} = 2 \, \text{A} \times 0.125 = 0.25 \, \text{A} \]

### Step 6: Convert to milliamperes if necessary
To express this in milliamperes:

\[ I_p = 0.25 \, \text{A} = 250 \, \text{mA} \]

### Final Answer
The current in the primary coil is **0.25 A** or **250 mA**.

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