What will be the deflection (in rad) of a moving iron instrument, when the inductance of the moving iron instrument is (20 + 4θ) μH, where θ is the deflection in radian from zero position and the deflection current is 5 A? Assuming spring constant k = 10 × 10-6 Nm/rad.

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SSC JE EE Previous Year Paper 6 (Held On: 25 Jan 2018 Morning)
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  1. 5
  2. 10
  3. 15
  4. 20

Answer (Detailed Solution Below)

Option 1 : 5
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Detailed Solution

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Concept:

Operating torque:

In moving iron instruments, the deflecting torque is given by

I is the operating current in Ampere

L is the inductance in Henry

θ is the deflection angle in radians

Deflection is directly proportional to the square of the RMS value of the operating current. Hence, this instrument possesses high operating torque.

Calculation:

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