Waec 2025 Physics Question 8

(a)(i) State the one condition under which a semiconductor is said to be doped. (ii) Define the terms: I. intrinsic semi-conductor; II. extrinsic semi-conductor. (b) The current, \( I \), through a \( P-N \) junction diode is plotted against the applied voltage, \( V \) for both forward reverse biases on a graph. With the aid of a suitable diagram, illustrate the current - voltage characteristics of the junction diode showing the current, \( I \), voltage, \( V \), forward bias and the reverse bias. (c) An aluminium metal is illuminated with light of wavelength \( 3.0 \times 10^{-7} m \). If the kinetic energy of the electron emitted is \( 1.5 \times 10^{-19} J \), calculate the: (i) maximum velocity of the photoelectron; (ii) workfunction of the metal. \[ \begin{array}{l} {\left[c=3.0 \times 10^{8} \mathrm{~ms}^{-1}, m_{c}=9.1 \times 10^{-31} \mathrm{~kg}, h\right.} \left.=6.6 \times 10^{-34} \mathrm{Js}\right] \end{array} \]