Правка разделов «Statement», «Solution», «Answer»

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### Statement
−$11.4.13.$ [Insert the problem statement]
+$11.4.13.$ The values of voltage, current, and phase shift between voltage and current in the load circuit are shown in a vector diagram. Determine the source EMF amplitude if $R=10$ ohms.
### Solution
−![For problem $11.4.13$ |931x513, 31%](../../img/11.4.13/11.4.13.png)
+![For problem $11.4.13$ |931x513, 50%](../../img/11.4.13/11.4.13.png)
−Let the current through the load (and the resistor $R$) be $I=(12\mbox{ A})e^{i\omega t}$, where $\omega$ is the angular frequency of the source. Then, the voltage drops across the load and the resistor are $V_L=(120\mbox{ V})e^{i(\omega t-\pi/3)}$ and
+Let the current through the load (and the resistor $R$) be $I=(12\mbox{ A})\cdot e^{i\omega t}$, where $\omega$ is the angular frequency of the source. Then, the voltage drops across the load and the resistor are $V_L=(120\mbox{ V})\cdot e^{i(\omega t-\pi/3)}$ and
−\[V_R=IR=(120\mbox{ V})e^{i\omega t},\]
+\[V_R=IR=(120\mbox{ V})\cdot e^{i\omega t},\]
respectively. Consequently, the EMF of the source is $\mathcal{E}=V_L+V_R$, which becomes
−\[\mathcal{E}=(120\mbox{ V})(e^{i\pi/6}+e^{-i\pi/6})e^{i(\omega t-\pi/6)}=(120\mbox{ V})\cdot2\cos\frac{\pi}{6}\cdot e^{i(\omega t-\pi/6).\]
+\[\mathcal{E}=(120\mbox{ V})\cdot(e^{i\pi/6}+e^{-i\pi/6})\cdot e^{i(\omega t-\pi/6)}=(120\mbox{ V})\cdot2\cos\frac{\pi}{6}\cdot e^{i(\omega t-\pi/6)}.\]
−Thus, the amplitude of the $EMF$ is $120\sqrt3\approx208$ V.
+Thus, the amplitude of the EMF is $120\sqrt3\approx208$ V.
#### Answer
−[Insert a concise answer or boxed result]
+$120\sqrt3\approx208$ V