Question

An AC source rated $100\text{V (rms)}$ supplies a current of $10\text{A (rms)}$ to a circuit. The average power delivered by the source

• A. Must be $1000\text{W}$
• B. May be $1000\text{W}$
• C. May be greater than 1000 W
• D. May be less than 1000 W

Answer 1

Answer: (B), (D)

May be less than 1000 W

We know that average power is given by
$P_{avg}=V_{rms}{I}_{rms}cos\varphi$
Given that
$V_{rms}=100\text{V}$ and
$I_{rms}=10\text{A}$

Now we know $\cos \varphi$ ranges from $-1\text{to}1$
But considering only the magnitude we can say
maximum value of $\cos \varphi =1$
minimum value of $\cos \varphi =0$
So it can have average power upto $1000\text{W}$
So only option (b) and (d) are correct