Answer
See answers.
Work Step by Step
a. Use Equation 18–9c to find the rms voltage.
$$\overline{P}=\frac{V_{rms}^2}{R}$$
$$V_{rms}=\sqrt{\overline{P}R}=\sqrt{(100W)(8\Omega)}=28.3V\approx 30V$$
Now apply equation 18–9a to find the rms current.
$$I_{rms}=\frac{\overline{P}}{V_{rms}}=\frac{100W}{28.28V}\approx 4A$$
b. Do the same thing, using the small power.
$$\overline{P}=\frac{V_{rms}^2}{R}$$
$$V_{rms}=\sqrt{\overline{P}R}=\sqrt{(1.0W)(8\Omega)}=2.83V\approx 3V$$
Now apply equation 18–9a to find the rms current.
$$I_{rms}=\frac{\overline{P}}{V_{rms}}=\frac{1.0W}{2.828V}\approx 0.4A$$