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NEETPhysicsAlternating Current

An unknown electrical device draws a steady current of 0.5 A when connected to a 20 V DC supply. When the same device is connected to a 20 V AC supply, it draws an rms current of 0.4 A . The power factor of the device when connected to the AC supply is

Options

  1. A1.25
  2. B0.6
  3. C0.2
  4. D0.8

Correct answer

D. 0.8

Step-by-step solution

When connected to a DC supply, the steady current indicates the device does not contain a series capacitor. It offers only resistance R . R = V_ DC I_ DC = 20 0.5 = 40 When connected to an AC supply, the device offers an impedance Z . Z = V_ AC I_ AC = 20 0.4 = 50 The power factor of the device is the ratio of its resistance to its impedance: = R Z = 40 50 = 0.8 Answer: 0.8

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