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  1. It x is the system reactance and r is its resistance, the power transferred is maximum when
    1. x = r
    2. x = √2r
    3. x = √3r
    4. x = 2r
Correct Option: C


I =
V1∠δ - V2∠0
Z∠θ

=
V1
∠(δ - ∠0) -
V2
∠- θ
ZZ

Power received, P2 = Re [V2I*]
= ReV2
V1
∠(θ - δ) -
V2
∠θ
ZZ

=
V1V2
cos(θ - δ) -
2
cos θ
ZZ

Let θ = 90° – α, then
=
V1V2
cos(90° - α - δ) -
2
cos(90° - α)
ZZ

=
V1V2
sin(α + δ) -
2
sin α
ZZ

P2 max =
V1V2
-
2
sin α[α + δ = 90°]
ZZ

As, sin α =
r
, then
Z

P2 max =
V1V2
-
2
.
r
r² + x²r² + x²r² + x²

For P2 max to be maximum,
dP2 max
= 0
dx

or V²2
x1
-
2xr
= 0
(r² + x²)2/3(r² + x²)²

Here V1 = V2
∴ r² + x² = 4r²
or x = 3r



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