Lesson Notes By Weeks and Term v4 - SHS 2
HEAT
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HEAT
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Subject: Physics
Class: SHS 2
Term: 1st Term
Week: 13
Grade code: 2.2.1.LI.2
Strand code: 2
Sub-strand code: 1
Content standard code: 2.2.1.CS.1
Indicator code: 2.2.1.LI.2
Theme: ENERGY
Subtheme: HEAT
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This lesson introduces the concepts of heat capacity and specific heat capacity. Understanding these concepts is fundamental to explaining everyday phenomena we experience in Ghana. From cooking our favourite meals like banku, where water takes a long time to boil, to understanding why the coast is cooler during the day than inland areas, the principles of specific heat capacity are all around us. This lesson will equip learners with the knowledge to define these terms, differentiate between them, and, most importantly, calculate the specific heat capacity of various substances using established scientific methods.
A. Differentiating Heat and Temperature Before we proceed, let's clarify two terms we often use interchangeably but which have different meanings in physics. Heat (Q): This is the energy that is transferred from a hotter object to a colder object due to the temperature difference between them. Its SI unit is the Joule (J). Temperature (θ or T): This is a measure of the degree of hotness or coldness of a body. It indicates the average kinetic energy of the particles in the substance. Its SI unit is the Kelvin (K), although we often use degrees Celsius (°C) in calculations involving temperature *change*. B. Heat Capacity (C) Imagine you have a solid metal block, like a piece of iron. The heat capacity is about the *entire block*. Definition: Heat Capacity is the quantity of heat energy required to raise the temperature of a *whole substance or body* by one degree Celsius (1°C) or one Kelvin (1K). Formula: `C = Q / Δθ` Where: `C` is the Heat Capacity `Q` is the heat energy supplied (in Joules, J) `Δθ` is the change in temperature (in K or °C) Units: The SI unit is Joules per Kelvin (J/K) or Joules per degree Celsius (J/°C). C. Specific Heat Capacity (c) Now, imagine you take just a small, standard piece of that iron block—specifically, a piece with a mass of 1 kilogram. The specific heat capacity is about this *standard mass*. Definition: Specific Heat Capacity is the quantity of heat energy required to raise the temperature of a *unit mass (e.g., 1 kg)* of a substance by one degree Celsius (1°C) or one Kelvin (1K). The word "specific" in physics often means "per unit mass". Formula: `c = Q / (m * Δθ)` Rearranging this gives the most commonly used form: `Q = mcΔθ` Where: `Q` is the heat energy supplied (in Joules, J) `m` is the mass of the substance (in kilograms, kg) `c` is the specific heat capacity (in J/kgK or J/kg°C) `Δθ` is the change in temperature (θ_final - θ_initial) (in K or °C)
Key Value to Remember: The specific heat capacity of water is approximately 4200 J/kg°C. This is a very high value, which is why water is so important for cooling and regulating temperature. D. Relationship between Heat Capacity (C) and Specific Heat Capacity (c) From our definitions, we can establish a simple relationship. Heat Capacity: `C = Q / Δθ` (Equation 1) Specific Heat Capacity: `Q = mcΔθ` (Equation 2)
Substitute Equation 2 into Equation 1: `C = (mcΔθ) / Δθ` `C = mc`
This is the relationship: The Heat Capacity of an object is its specific heat capacity multiplied by its mass.