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A step-down transformer has a power output of 50 W and efficiency of 80%. if...

Physics
JAMB 2008

A step-down transformer has a power output of 50 W and efficiency of 80%. if the mains supply voltage is 200 v, calculate the primary current of the transformer.

  • A. 0.31 A
  • B. 3.20 A
  • C. 3.40 A
  • D. 5.00 A
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Correct Answer: Option A
Explanation

To find the primary current of the step-down transformer, we follow these steps:

1. Calculate the Power Input:
   The efficiency (\( \eta \)) of the transformer is given by:
   \(\eta = \frac{\text{Power Output}}{\text{Power Input}} \times 100\)
   Rearranging gives:
   \(\text{Power Input} = \frac{\text{Power Output}}{\eta}\)

   Given:
   - Power Output = 50 W
   - Efficiency = 80\% = 0.80

   Thus,
   \(\text{Power Input} = \frac{50 \, \text{W}}{0.80} = 62.5 \, \text{W}\)

2. Calculate the Primary Current:
   The power input can also be expressed in terms of voltage and current:
   \(\text{Power Input} = V_p \times I_p\)
   Where:
   - \( V_p \) = primary voltage (given as 200 V)
   - \( I_p \) = primary current (what we want to find)

   Rearranging gives:
   \( I_p = \frac{\text{Power Input}}{V_p}\)

   Now substituting the values:
   \(I_p = \frac{62.5 \, \text{W}}{200 \, \text{V}} = 0.3125 \, \text{A}\)

Thus, the primary current of the transformer is: 0.3125A

There is an explanation video available below.


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Explanation Video

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