Lesson Notes By Weeks and Term v4 - SHS 3
HEAT
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HEAT
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Subject: Physics
Class: SHS 3
Term: 1st Term
Week: 18
Grade code: 3.2.1.LI.3
Strand code: 2
Sub-strand code: 1
Content standard code: 3.2.1.CS.1
Indicator code: 3.2.1.LI.3
Theme: ENERGY
Subtheme: HEAT
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This lesson explores the phenomenon of thermal expansion, focusing on how different materials, particularly metals, change in size when their temperature changes. Understanding this concept is crucial for our everyday lives here in Ghana. From the gaps left in the Adome Bridge to prevent it from buckling in the hot sun, to the way our electrical cables from ECG sag more during a hot afternoon, the effects of thermal expansion are all around us. By understanding the property of linear expansivity, we can predict, design, and build structures and devices that are safe and efficient in our warm climate.
A. What is Thermal Expansion? When most substances are heated, they expand. When they are cooled, they contract. This change in size (length, area, or volume) due to a change in temperature is called thermal expansion.
Why does it happen? (The Particle Model) All matter is made up of tiny particles (atoms or molecules) that are in constant motion. In a solid, these particles are held in fixed positions but vibrate around these positions. When we add heat energy, the particles absorb this energy and their kinetic energy increases. This causes them to vibrate more vigorously and with a larger amplitude. As they vibrate more, they push their neighbouring particles further away, increasing the average distance between them. This increase in the average separation of particles results in the expansion of the solid in all dimensions. B. Types of Thermal Expansion There are three main types of thermal expansion, depending on the dimension we are considering: Linear Expansion: Expansion in one dimension (length). This is most noticeable in objects like rods, wires, and pipes. Area (or Superficial) Expansion: Expansion in two dimensions (length and width), resulting in an increase in area. This is seen in thin sheets or plates of metal. Volume (or Cubical) Expansion: Expansion in all three dimensions, resulting in an increase in volume. This applies to all solids, liquids, and gases.
*This lesson focuses primarily on Linear Expansion as specified by the curriculum indicator.* C. Linear Expansion and the Coefficient of Linear Expansivity (α)
Linear expansion is the increase in the length of a solid when it is heated.