$(i)$ Name the type of diode whose characteristics are shown in figure $(a)$ and figure $(b)$.
$(ii)$ What does the point $P$ in figure $(a)$ represent?
$(iii)$ What do the points $P$ and $Q$ in figure $(b)$ represent?

(N/A) $(i)$ Figure $(a)$ shows the characteristics of a Zener diode,and figure $(b)$ shows the characteristics of a solar cell.
$(ii)$ Point $P$ in figure $(a)$ represents the reverse breakdown voltage,also known as the Zener voltage $(V_Z)$.
$(iii)$ Point $P$ in figure $(b)$ represents the open-circuit voltage $(V_{OC})$. This is the voltage across the solar cell when the net current through it is zero. At this point,the forward current due to the applied voltage exactly cancels the photocurrent generated by light.
Point $Q$ in figure $(b)$ represents the short-circuit current $(I_{SC})$. This is the current flowing through the solar cell when the external voltage applied across it is zero,under illumination.