Question

A step-down transformer is used to reduce the main supply from $V_1$ volt to $V_2$ volt. The primary coil draws a current $I_1$ A and the secondary coil draws $I_2$ A ($I_1 \lt I_2$). The ratio of input power to output power is

• A. $\frac{V_1 V_2}{I_1 I_2}$
• B. $\frac{V_1 I_1}{V_2 I_2}$
• C. $\frac{I_1 I_2}{V_1 V_2}$
• D. $\frac{V_1 I_2}{V_2 I_1}$

Hint:

Always remember that power is simply voltage multiplied by current ($P = VI$). Therefore, the input power must contain the primary parameters ($V_1 I_1$) in the numerator, and the output power must contain the secondary parameters ($V_2 I_2$) in the denominator.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
For a step-down transformer with primary voltage V₁, current I₁, and secondary V₂, I₂, find the input to output power ratio.

Step 2: Key Formula or Approach:
Power P = V × I. Input power = V₁I₁, output power = V₂I₂. Ratio = P_in / P_out.

Step 3: Detailed Explanation:
P_in = V₁I₁, P_out = V₂I₂. The ratio is V₁I₁ / V₂I₂.

Step 4: Final Answer:
Ratio is V₁I₁ / V₂I₂, matching option (B).