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The r.m.s current of an alternating current given by, \(i = 4\sqrt{2}\sin\omega t + 3\sqrt{2}\cos\omega t\) is

  • A.5 \(A\)
  • B.3\(A\)
  • C.5\(\sqrt{2}A\)
  • D.2.5\(A\)
  • E.7\(\sqrt{2}A\)

Answer: A

The r.m.s. current is 5 A.

The two terms combine into one sinusoid with peak value

\[ \begin{aligned} I_0 &= \sqrt{(4\sqrt{2})^{2} + (3\sqrt{2})^{2}} = \sqrt{32 + 18} \\ &= \sqrt{50} = 5\sqrt{2}\ \text{A} \\ I_{rms} &= \frac{I_0}{\sqrt{2}} = 5\ \text{A} \end{aligned} \]

\(5\sqrt{2}\) A is the peak value, not the r.m.s. value, and \(7\sqrt{2}\) A simply adds the two amplitudes.

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