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Electric circuits miscellaneous

  1. The voltage across the capacitor, as shown in the figure, is expressed as
    Vc (t) = A1 sin(ω1 t – θ1) + A2 sin(ω2 t – θ2)

    The values of A1 and A2 respectively, are
    1. 2.0 and 1.98
    2. 2.0 and 4.20
    3. 2.5 and 3.50
    4. 5.0 and 6.40
Correct Option: A

Opening current source,

VC1(t) =
20 sin 10t
1
=
20 sin 10t
R +
1
1C1RC + 1
1C

=
20 sin 10t
[ ω1 = 10 rad / sec ]
1 + j10

=
20 sin( 10t - θ1)
, where θ1 = tan-1(10)
101

VC1(t) ≅ 2 sin (10t – θ1) ...(A)
Now, shorting voltage source, we have
VC2(t) =
10 sin 5t
1
R +
1
2C
2C

=
10 sin 5t
=
10 sin 5t
[ ω2 = 5 rad / sec ]
1 + jω2CR1 + 5j

=
10
sin( 5t - θ2) , where θ2 = tan-1(5)
26

VC2(t) ≅ 1.97 sin(5t – θ2) ...(B)
From equation (A) and equation (B), we have
A1 = 2.0, A2 = 1.98



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