Question

A step down transformer has turns ratio 20:1. If 8V are applied across \(0.4 \Omega\) secondary then the primary current will be

• A. \(0.5\) A
• B. \(1\) A
• C. \(2\) A
• D. \(4\) A

Hint:

Find the secondary current, then divide by the turns ratio.

Answer 1

The Correct Option is B

Step 1: Power conservation:
Secondary power $= V_sI_s = \dfrac{V_s^2}{R} = \dfrac{64}{0.4} = 160$ W.

Step 2: Primary voltage:
$V_p = 20V_s = 160$ V.

Step 3: Primary current:
$I_p = \dfrac{160}{160} = 1$ A, option (B).

Final Answer:
The primary current is 1 A. \[ \boxed{\text{(B) }1\ \text{A}} \]