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Diodes — KCSE Physics

KCSE Physics · 109 practice questions · 7 syllabus objectives

36 easy37 medium36 hard

What You'll Learn

Key learning outcomes for this topic, aligned to the KNEC KCSE syllabus.

Describe the structure and uses of a light-emitting diode (LED) and a photodiode

Explain the structure and working principle of a p-n junction diode; distinguish between forward and reverse bias

Describe how a diode is used in half-wave and full-wave rectification; sketch the input and output voltage waveforms

Describe half-wave and full-wave rectification; explain capacitor smoothing and sketch output waveforms

Draw circuit diagrams for forward and reverse biased p-n junction diodes; explain observations

Sketch I-V characteristics for forward and reverse biased diodes; distinguish ohmic and non-ohmic behaviour

Diodes

Sample Questions

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1
easySHORT ANSWER3 marks

State three differences between half-wave and full-wave rectification. (3 marks)

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Part (a) — 3 marks
Half-wave rectification only uses one half of the AC cycle, while full-wave uses both halves (1 mk)
Full-wave rectification produces a smoother output voltage than half-wave (1 mk)
Half-wave rectification requires one diode, while full-wave typically requires two or four diodes (1 mk)
2
easySHORT ANSWER3 marks

State the behaviour of a diode when it is forward biased and how this differs from its behaviour when reverse biased. (3 marks)

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Part (a) — 1 mark
Allows significant current to flow through the diode (1 mk)
Part (b) — 1 mark
Blocks current flow, allowing only a negligible leakage current (1 mk)
Part (c) — 1 mark
In forward bias, current flows; in reverse bias, current is blocked (1 mk)
3
easySHORT ANSWER3 marks

Explain the operation of a p-n junction diode when it is forward biased and state the effect on current flow. (3 marks)

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Part (a) — 2 marks
The p-side is connected to the positive terminal of the power supply, allowing current to flow (1 mk)
The applied voltage reduces the barrier potential, facilitating charge carrier movement across the junction (1 mk)
Part (b) — 1 mark
Current flow is significant and increases with the applied voltage (1 mk)
4

State two differences between a light-emitting diode (LED) and a photodiode. (2 marks)

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KNEC Aligned

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