# The primary and secondary coil of a transformer each have an inductance of 200 × 10-6H.

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The primary and secondary coil of a transformer each have an inductance of 200 × 10-6H. The mutual inductance (M) between the windings is 4 × 10-6H. What percentage of the flux from one coil reaches the other?

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Data: LP = LS = 2 × 10-4 H, M = 4 × 10-6 H
M = K$$\sqrt{L_{\mathrm{P}} L_{\mathrm{S}}}$$
The coupling coefficient is
K = $$\frac{M}{\sqrt{L_{\mathrm{P}} L_{\mathrm{S}}}}=\frac{4 \times 10^{-6}}{\sqrt{\left(2 \times 10^{-4}\right)^{2}}}=\frac{4 \times 10^{-6}}{2 \times 10^{-4}}$$
= 2 × 10-2
Therefore, the percentage of flux of the primary reaching the secondary is
0.02 × 100% = 2%