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# A transformer has an efficiency of $80\%$ and works at 100 volt and 4 kw. If the secondary voltage is $240\;volt$ calculate the primary and secondary currents

$\begin{array}{1 1} I_p= 40\;A,I_s=13.3\;A \\ I_p= 13.3\;A,I_s=40\;A \\ I_p= 4\;A,I_s=13.3\;A \\ I_p= 4\;A,I_s=1.33\;A \end{array}$

given $n = 80\%$
$E_p= 100 v$
$E_pI_p= 4\;kw$
$\qquad= 4000\;w$
$I_p= \large\frac{E_p I_p}{E_p}$
$\qquad= \large\frac{4 \times 1000}{100}$
$\qquad= 40 \;A$
$n= \large\frac{80 \times 100 \times 40}{240 \times 100}$
$\quad= 13.3\;A$