Question

An AC source rated 100 V (rms) supplies a current of 10 A (rms) to a circuit. The average power delivered by the source
(a) must be 1000 W
(b) may be 1000 W
(c) may be greater than 1000 W
(d) may be less than 1000 W

Answer 1

(b) may be 1000 W
(d) may be less than 1000 W

The average power delivered by an AC source is given by,
`P_{avg} = V_{rms}I_rms cos Ø`
Given ;
`V_rms = 100V` 
`Irms = 10 A`
⇒ `P_{avg} = 1000 cos `Ø   
`therefore Ø ∈ (-pi/2, pi/2)`
⇒ cos Ø ∈ (0,1),
`therefore 0  ≤ P_{avg]  ≤ 1000`