1.

Prove that in series combination of electrical appliances, the reciprocal of total power consumption is equal to the sum of the reciprocal of the powers of the individual appliances.

Answer» Let `P_(1),P_(2),P_(3)` be the powers of electrical appliances at V volt. If `R_(1), R_(2), R_(3)` are their resistance, then
`R_(1)=V^(2)/P_(1), R_(2) = V^(2)/P_(2) and R_(3) = V^(2)/P_(3)`
When the electrical appliances are connected in series, then effective resistance, R is
`R = R_(1) + R_(2) +R_(2)`
or `R/V^(2) = R_(1)/V^(2) + R_(2)/V^(2) + R_(3)/V^(2)`
or `1/(V^(2)//R) = 1/(V^(2)//R_(1)) + 1/(V^(2)//R_(2)) + 1/(V^(2)//R_(3))`
or `1/P = 1/P_(1) + 1/P_(2) + 1/P_(3)`


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