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Concepts Of Physics MCQ Edition [Volume 2]PhysicsAlternating Current

Determine the time needed for a 50 Hz alternating current to change its value from zero to its rms value.

Options

  1. A0.020 s
  2. B0.0050 s
  3. C0.0025 s
  4. D0.010 s

Correct answer

C. 0.0025 s

Step-by-step solution

The equation of an alternating current is I = I₀ ( t) . The rms value of the current is I_ rms = I₀ 2 . Substituting I = I_ rms in the equation, we get: I₀ 2 = I₀ ( t) ( t) = 1 2 t = 4 Using = 2 f , we have: 2 f t = 4 t = 1 8f Given f = 50 Hz , substituting the value of f : t = 1 8 50 = 1 400 = 0.0025 s

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