Question

Current I = – 1 + \(\sqrt{2}\) (sin (ωt + 60°)) A is passed through three meters. The respective readings will be?

(a) \(\sqrt{2}\) A, \(\sqrt{2}\) A and 1 A

(b) 1 A, \(\sqrt{2}\) A and 1 A

(c) – 1 A, \(\sqrt{2}\) A and \(\sqrt{2}\) A

(d) -1 A, 1 A and 1 A

I got this question in final exam.

My question comes from Advanced Problems on Filters in division Filters and Attenuators of Network Theory

Answer 1

The correct option is (c) – 1 A, \(\sqrt{2}\) A and \(\sqrt{2}\) A

The explanation: We know that a PMMC instrument reads only DC value and since it is a centre zero type, so it will give – 1.

So, rms = \(\sqrt{1^2 + (\frac{\sqrt{2}}{\sqrt{2}})^2} = \sqrt{2}\) A

Moving iron also reads rms value, so its reading will also be \(\sqrt{2}\) A.