WAEC Physics 2025 Theory — Question 9
Question 9 of 34 from the West African Examinations Council (WAEC) Physics 2025 Theory paper, with the correct answer and a full explanation.
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8(b) The current, I, through a P–N junction diode is plotted against the applied voltage, V, for both forward and 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.
Model answer
In forward bias, current, I, rises slowly at first then increases sharply (almost exponentially) once the applied voltage, V, exceeds the diode's threshold/turn-on voltage. In reverse bias, only a very small (near-zero) leakage/reverse-saturation current flows as V is increased in the negative direction, until the breakdown voltage is reached, beyond which current increases sharply again.
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