Class 4 (4th Engineer) MET 📅 Sep 2025

Exam Question

(a) Describe the principle of operation of EACH of the following detecting elements: (8)

(i) Bi-metal strips

(ii) Thermisters

(b) Explain, with the aid of sketches, typical applications where the devices described in (a) may be employed in high voltage electrical systems. (8)

Reference Answer

### (a) Principle of Operation of Detecting Elements
#### (i) Bi-metal Strips (8 marks)
**1. Fundamental Principle:**
The operation of a bimetallic strip is based on the principle of **differential thermal expansion**. This principle relies on two key physical properties of metals, as stated in the reference material:

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