Can the instantaneous power output of an AC source ever be negative? Can the average power output be negative?

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Payal Gupta | Contributor-Level 10

8 months ago

This is a short answer type question as classified in NCERT Exemplar

E=E₀sinwt

And current I=I₀sin (wt $\frac{+}{-} \emptyset$ )

Power, P= EI = E₀sinwt = E₀I₀sinwtsin (wt+ $\emptyset$ )

= $\frac{E_{0} I_{0}}{2}$ [cos $\emptyset - c o s (2 w t + \emptyset)$ ]………… (1)

Pav= $\frac{V_{0}}{\sqrt[]{2}} \frac{I_{0}}{\sqrt[]{2}}$ cos $\emptyset$ =V_rmsI_rmscos $\emptyset$ ………. (2)

From eqn 1 ……But when cos $\emptyset$ < cos (2wt+ $∅)$

P<0 power can be nagative of an AC source

From eqn 2……… P_av>0

cos $\emptyset$ =R/Z>0 average power can not be negative

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