A step-down transformer is used on a $1000 V$ line to deliver $20 A$ at $120 V$ at the secondary coil. If the efficiency of the transformer is $80 %$ , the current drawn from the line is

$3 A$

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$30 A$

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$0.3 A$

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$2.4 A$

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Solution

The correct option is A
$3 A$

Step 1: Given data
Input voltage, $V_{1} = 1000 V$
Output voltage, $V_{2} = 120 V$
Output current, $I_{2} = 20 A$
Efficiency of the transformer $= 80 %$
Step 2: Finding the input current drawn from the line.
We know that,
Efficiency of the transformer $= \frac{O u t p u t p o w e r}{I n p u t p o w e r}$
$80 % = \frac{V_{2} I_{2}}{V_{1} I_{1}}$ $[∵ P o w e r = v o l t a g e \times c u r r e n t]$
$\frac{80}{100} = \frac{120 \times 20}{1000 \times I_{1}}$
$I_{1} = \frac{120 \times 20 \times 100}{1000 \times 80}$
$I_{1} = 3 A$
Hence, option A is correct the current drawn from the line is $3 A$ .

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A step-down transformer is used on a 1000V line to deliver 20A at 120V at the secondary coil. If the efficiency of the transformer is 80%, the current drawn from the line is

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