Lesson Notes By Weeks and Term v4 - SHS 2
WAVES
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WAVES
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Subject: Physics
Class: SHS 2
Term: 1st Term
Week: 15
Grade code: 2.2.1.LI.4
Strand code: 2
Sub-strand code: 2
Content standard code: 2.2.1.CS.1
Indicator code: 2.2.1.LI.4
Theme: ENER GY
Subtheme: WAVES
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This lesson explores the fascinating concept of "hidden heat" or latent heat. We experience phase changes every day in Ghana: when we boil water to make *koko* or *eba*, when ice blocks we buy for a party melt into water, or when we feel cooler after sweating on a hot day. Today, we will learn the physics behind these changes. We will discover that adding heat to a substance does not always increase its temperature. This knowledge is fundamental to understanding everything from cooking and refrigeration to weather patterns.
Part 1: Review of Phase Changes
Before we discuss latent heat, let's refresh our understanding of the states of matter and the transitions between them. This is our foundation. Melting: The process by which a substance changes from a solid state to a liquid state at a constant temperature (the melting point). For example, ice melting to water. Freezing: The opposite of melting. It is the process by which a substance changes from a liquid state to a solid state at a constant temperature (the freezing point). For example, water turning into ice in a freezer. Boiling: The process by which a liquid changes into a gas (vapour) at a specific constant temperature (the boiling point). Bubbles form throughout the liquid. For example, water boiling at 100°C to form steam. Evaporation: The process by which a liquid changes into a gas (vapour) at *any* temperature below the boiling point. It occurs only at the surface of the liquid. For example, a puddle of water drying up in the sun.
Key Idea: During any of these phase changes, the temperature of the substance DOES NOT CHANGE, even though heat is being added or removed. Where does this energy go? Part 2: Latent Heat
The word "latent" means hidden. Latent heat is the "hidden" energy absorbed or released by a substance during a phase change at a constant temperature. When a solid melts or a liquid boils, energy is absorbed. This energy is not used to increase the kinetic energy of the molecules (which would raise the temperature). Instead, it is used to break the bonds holding the molecules together in their fixed solid structure or close liquid arrangement. When a gas condenses or a liquid freezes, energy is released as new, stronger bonds are formed.