Class 4 (4th Engineer) MET 📅 Aug 2025

Exam Question

(a) What is a zener diode? (6)

(b) Find the generated e.m.f./conductor of a 6-pole d.c generator having a magnetic flux/pole of 64m Wb and a speed of 1000 rev/min. If there are 468 conductors, connected in six parallel circuits, calculate the total generated e.m.f. of the machine. Find also the total power developed by the armature when the current in each conductor is 50A. (10)

Reference Answer

### (a) Zener Diode (6 Marks)
A Zener diode is a specialized silicon p-n junction semiconductor device, specifically designed to operate reliably in the reverse-biased breakdown region. Unlike a conventional diode, which is permanently damaged if its reverse breakdown voltage is exceeded, the Zener diode is manufactured to handle breakdown without failure, provided the current is limited by an external resistor.
**1. Principle of Operation:**
* **Forward Bias:** When forward biased (anode positive, cathode negative), a Zener diode behaves like a standard rectifier diode, allowing current to flow once the forward voltage drop (approx. 0.7V for silicon) is reached.

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