Physics - Current Electricity Question with Solution | TestHub

A. The terminal voltage is $V=\mathcal{E}-Ir=\mathcal{E}\frac{R}{R+r}$. As $R\to \infty$, $V\to \mathcal{E}$, which is the maximum possible terminal voltage. B. The power delivered to the external resistance is $P=I^{2}R=(\frac{\mathcal{E}}{R+r}{)}^{2}R$. For maximum power, $R=r$. C. The current $I=\frac{\mathcal{E}}{R+r}$ is maximum when $R=0$ (short circuit), not when $R=r$. D. The efficiency $\eta =\frac{\text{Power in }R}{\text{Total power generated}}=\frac{I^{2}R}{I^2(R+r)}=\frac{R}{R+r}$.