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Electric circuits miscellaneous

  1. In the circuit given in the figure, the power consumed in the resistance R is measured when one source is acting at a time, these values are 18 W, 50 W and 98 W. When all the sources are acting simultaneously, possible maximum and minimum values of power in R will be

    1. 98 W and 18 W
    2. 166 W and 18 W
    3. 450 W and 2 W
    4. 166 W and 2 W
Correct Option: C

P1 = 18 =
E12
R

P2 = 50 =
E22
R

P3 = 98 =
E32
R

Maximum power, Pmax =
(E1 + E2 + E3)2
R

=
E12 + E22 + E32 + 2E1E2 + 2E2E3 + 2E3E1
R

⇒ Pmax = P1 + P2 + P3 + 2(√P1P2 + √P2P3 + √P3P1)
= 18 + 50 + 98 + 2 √18 × 50 + 2 √50 × 98 + 2 √18 × 98 = 450 watts
Minimum power, Pmax =
(E1 - E2 - E3)2
R

= P1 + P2 + P3 - 2√P1P3 - 2√P2P3 + 2√P1P2)
= 18 + 50 + 98 - 2 √18 × 98 - 2 √50 × 98 + 2 √18 × 50 = 2 watts



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