a b c d

d

$ I = \frac{V}{R} = 11 sin 100\pi t$ $I_{peak} = 11$ $ 11 = 11 sin 100\pi t_1 \Rightarrow sin 100\pi t_1 = sin \frac{\pi}{2}$ $ t_1 = \frac{1}{200}$ $ I_{rms} = \frac{11}{\sqrt 2} = 11 sin 100\pi t_2 \Rightarrow sin 100\pi t_2 = \frac{\pi}{4}$ $\Rightarrow t_2 = \frac{1}{400}$ $ \Delta t = t_1 - t_2 = \frac{1}{200} - \frac{1}{400} = \frac{1}{400} = 2.5\times 10^{-3}$