given:
efficiency e \(=80 \%\)
\(\mathrm{V}_{\mathrm{p}}=25 \mathrm{~V}\)
\(V_{\mathrm{s}}=240 \mathrm{~V}\)
\(P_{\mathrm{s}}=100 \mathrm{~W}\)
\(I_p=? P_{\mathrm{s}}=V_{\mathrm{s}} \mathrm{I}_5, I_5=\frac{P_{\mathrm{s}}}{V_5}\)
\(=\frac{V_S I_S}{V_p \times I_p} \times 100 \%\)
\(80 \%=\frac{240 \times 0.4167}{25 \times 1_p} \times 100 \%\)
\(\frac{80}{100}=\frac{100.008}{25 \times V_p}\)
\(0.8 \times 25 \times \mathrm{I}_{\mathrm{p}}=100.008\)
\(\mathrm{I}_p=\frac{100.008}{0.8 \times 25}\)
\(I_p=4.0 \mathrm{~A}\)