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 step down transformer has turns ratio 20:1. If 8V are applied across \(0.4 \Omega\) secondary then the primary current will be
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Find the secondary current, then divide by the turns ratio.
Updated On: Oct 1, 2026
- \(0.5\) A
- \(1\) A
- \(2\) A
- \(4\) A
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The Correct Option is B
Solution and Explanation
Step 1: Understanding the Concept:
In an ideal transformer, \(\dfrac{I_p}{I_s} = \dfrac{N_s}{N_p}\). A step down transformer with ratio 20:1 has \(N_p : N_s = 20 : 1\).
Step 2: Secondary current:
The 8 V is across the \(0.4\ \Omega\) secondary:
\[ I_s = \frac{8}{0.4} = 20\ \text{A} \]
Step 3: Primary current:
\[ I_p = I_s\cdot\frac{N_s}{N_p} = 20\times\frac1{20} = 1\ \text{A} \]
Step 4: Check:
Option (B). Power check: secondary power \(= 8\times20 = 160\) W, primary voltage \(= 160\) V, and \(160\times1 = 160\) W.
Final Answer:
Secondary current 20 A, divided by 20 gives 1 A. \[ \boxed{\text{(B) }1\ \text{A}} \]
In an ideal transformer, \(\dfrac{I_p}{I_s} = \dfrac{N_s}{N_p}\). A step down transformer with ratio 20:1 has \(N_p : N_s = 20 : 1\).
Step 2: Secondary current:
The 8 V is across the \(0.4\ \Omega\) secondary:
\[ I_s = \frac{8}{0.4} = 20\ \text{A} \]
Step 3: Primary current:
\[ I_p = I_s\cdot\frac{N_s}{N_p} = 20\times\frac1{20} = 1\ \text{A} \]
Step 4: Check:
Option (B). Power check: secondary power \(= 8\times20 = 160\) W, primary voltage \(= 160\) V, and \(160\times1 = 160\) W.
Final Answer:
Secondary current 20 A, divided by 20 gives 1 A. \[ \boxed{\text{(B) }1\ \text{A}} \]
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