Lesson Notes By Weeks and Term v4 - SHS 3

Lesson Video

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Performance objectives

• Define linear, area, and volume expansivity.
• Calculate the different types of expansivity for metals.
• Explain the importance of expansion in applications like bimetallic strips.
• Solve practical problems involving thermal expansion.

Lesson summary

This lesson explores the phenomenon of thermal expansion in solids. We will investigate how the dimensions of solid materials, particularly metals, change in response to changes in temperature. Understanding this concept is crucial for many real-world engineering and construction applications we see every day in Ghana—from the gaps in our concrete roads and bridges like the Adomi Bridge, to the way electricity cables from ECG are hung, and even how the automatic cut-off in an electric iron works. We will learn the scientific principles and mathematical formulas that govern these changes.

Lesson notes

2.1 What is Thermal Expansion?

At the microscopic level, all solids are made of atoms or molecules that are constantly vibrating. When we heat a solid, we are supplying it with thermal energy. This energy increases the kinetic energy of the particles, causing them to vibrate more vigorously and over a larger amplitude. As they vibrate more, they push their neighbours further away, causing the average distance between the particles to increase. This increase in the average separation of particles results in an overall increase in the size (length, area, or volume) of the solid. This phenomenon is called thermal expansion.

In simple terms: When most substances get hotter, they expand. When they get cooler, they contract. 2.2 Types of Thermal Expansion

We study thermal expansion in one, two, and three dimensions.

Evaluation guide

• Calculate the linear, area, and volume expansivities of metals.
• Think pair share :
• Let learners discuss the importance of expansion and how a bimetallic strip can be used as an
• electric circuit breaker .