Class: Senior Secondary School 2 (SS2 / SSS2)
Term: First Term
Week: 3
Age: 16 years
Duration: 45 minutes
Subject: Physics
Curriculum Theme: Energy
Previous Lesson: Heat Energy Measurement: Specific Heat Capacity and Method of Mixtures.
Topic: HEAT ENERGY MEASUREMENT
Subject Matter: Meaning of latent heat (heat absorbed or released without temperature change), latent heat (fusion of ice, vaporization of steam), evaporation boiling and sublimation (changes of state), relative humidity and dew point (meaning and simple determination)

Specific Objectives

By the end of the lesson, pupils should be able to:

Cognitive Domain:

Define latent heat, specific latent heat of fusion, and specific latent heat of vaporization.
Differentiate between evaporation, boiling, and sublimation.
Define relative humidity and dew point.
State the formulas for specific latent heat calculations.

Affective Domain:

Appreciate the importance of latent heat in everyday phenomena.
Value accurate measurements in experimental determination.

Psychomotor Domain:

Outline the procedure for determining specific latent heat of fusion or vaporization by the method of mixtures.
Solve simple problems involving specific latent heat.

Collaborate effectively in groups during discussions and experimental procedures.

Reference Materials

The following resources were used in planning this lesson:

Senior Secondary Schools Education Curriculum
State Unified Scheme of Work
New School Physics by M.W. Anyakoha
Physics for Senior Secondary Schools by P.N. Okeke and P.N. Anyakoha

Instructional Materials

The teacher will teach this lesson with the aid of:

Textbook
Equipped laboratory (calorimeter, thermometer, weighing balance, ice, steam generator, heater)
Charts illustrating changes of state and humidity concepts

Rationale for the Lesson

This lesson helps pupils understand how heat energy can be absorbed or released without changing temperature during phase changes. It is important for comprehending natural phenomena like weather patterns and industrial processes involving heating and cooling.

Prerequisite/Previous Knowledge

Pupils should have a basic understanding of heat, temperature, states of matter, and the concept of specific heat capacity.

Lesson Content/Board Summary

HEAT ENERGY MEASUREMENT

Latent Heat

Latent heat is the heat energy absorbed or released by a substance during a phase change (e.g., melting, boiling, freezing, condensation) without a change in its temperature. It is often referred to as “hidden heat.”

Specific Latent Heat of Fusion (L_f)

The specific latent heat of fusion is the amount of heat energy required to change a unit mass of a solid substance into a liquid at its melting point without a change in temperature.

Formula: Q = mL_f
Where:
- Q = amount of heat energy (Joules, J)
- m = mass of the substance (kilograms, kg)
- L_f = specific latent heat of fusion (Joules per kilogram, J/kg)

Example 1: Calculate the heat energy required to melt 0.5 kg of ice at 0°C. (Specific latent heat of fusion of ice = 3.34 x 10⁵ J/kg)

Step 1: Identify the given values.
- Mass (m) = 0.5 kg
- Specific latent heat of fusion (L_f) = 3.34 x 10⁵ J/kg
Step 2: State the formula.
- Q = mL_f
Step 3: Substitute the values and calculate.
- Q = 0.5 kg * 3.34 x 10⁵ J/kg
- Q = 1.67 x 10⁵ J

Specific Latent Heat of Vaporization (L_v)

The specific latent heat of vaporization is the amount of heat energy required to change a unit mass of a liquid substance into a gas at its boiling point without a change in temperature.

Formula: Q = mL_v
Where:
- Q = amount of heat energy (Joules, J)
- m = mass of the substance (kilograms, kg)
- L_v = specific latent heat of vaporization (Joules per kilogram, J/kg)

Example 2: How much heat energy is needed to convert 0.2 kg of water into steam at 100°C? (Specific latent heat of vaporization of water = 2.26 x 10⁶ J/kg)

Step 1: Identify the given values.
- Mass (m) = 0.2 kg
- Specific latent heat of vaporization (L_v) = 2.26 x 10⁶ J/kg
Step 2: State the formula.
- Q = mL_v
Step 3: Substitute the values and calculate.
- Q = 0.2 kg * 2.26 x 10⁶ J/kg
- Q = 4.52 x 10⁵ J

Determination by Method of Mixtures: The principle is that heat lost by a hotter substance equals the heat gained by a colder substance (and the calorimeter) until thermal equilibrium is reached.

Changes of State: Evaporation, Boiling, Sublimation

These are processes by which a substance changes from one physical state to another.

Evaporation:
- The process by which a liquid changes into a gas (vapour) at a temperature below its boiling point.
- It is a surface phenomenon.
- Examples: Wet clothes drying, puddles disappearing.
Boiling:
- The rapid vaporization of a liquid that occurs when a liquid is heated to its boiling point.
- It occurs throughout the bulk of the liquid, forming bubbles.
- Example: Water heated to 100°C turns into steam.
Sublimation:
- The process by which a solid changes directly into a gas without passing through the liquid state.
- Example: Dry ice (solid carbon dioxide) turning into gas, naphthalene balls shrinking.

Relative Humidity and Dew Point

Relative Humidity (RH):
- The ratio of the actual amount of water vapour present in the air to the maximum amount of water vapour the air can hold at the same temperature, expressed as a percentage.
- Formula: RH = (Actual Vapour Pressure / Saturated Vapour Pressure) x 100%
- It is commonly determined using a wet and dry bulb hygrometer.
Dew Point:
- The temperature at which a parcel of air becomes saturated with water vapour and condensation begins to form (e.g., dew, fog, clouds).
- It can be determined by cooling a polished metal can containing water and ice until dew forms on its surface.

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher asks pupils what happens to ice when left outside and what happens when water boils. The teacher then introduces the concept of hidden heat involved in these changes.
Pupils’ Activity: Pupils respond to the questions, recalling concepts of melting and boiling.
Learning Point: Pupils connect prior knowledge to the new topic of heat energy measurement.

Step 2: Explanation of Latent Heat

Time: 5 minutes
Teaching Skill: Explanation
Teacher’s Activity: The teacher defines latent heat, explaining that it is heat absorbed or released during a phase change without temperature alteration. The teacher distinguishes between latent heat of fusion and vaporization.
Pupils’ Activity: Pupils listen attentively and take notes on the definitions.
Learning Point: Pupils understand the meaning of latent heat and its types.

Step 3: Specific Latent Heat and Formulas

Time: 10 minutes
Teaching Skill: Demonstration/Explanation
Teacher’s Activity: The teacher explains specific latent heat of fusion (L_f) and vaporization (L_v), writing their formulas (Q = mL_f and Q = mL_v) on the board. The teacher works through the two examples provided in the board summary.
Pupils’ Activity: Pupils copy the formulas and examples, asking questions for clarification.
Learning Point: Pupils learn the formulas and how to apply them in calculations.

Step 4: Experimental Determination (Method of Mixtures)

Time: 5 minutes
Teaching Skill: Guidance/Discussion
Teacher’s Activity: The teacher guides pupils on the principle of determining specific latent heat of fusion of ice and latent heat of vaporization of steam by the method of mixtures, discussing the procedure and types of readings taken.
Pupils’ Activity: Pupils participate in the discussion, describing the steps and types of measurements needed.
Learning Point: Pupils understand the theoretical basis and procedural steps for experimental determination.

Step 5: Changes of State

Time: 5 minutes
Teaching Skill: Explanation/Examples
Teacher’s Activity: The teacher explains evaporation, boiling, and sublimation, providing examples for each and highlighting their differences.
Pupils’ Activity: Pupils listen, take notes, and contribute examples from daily life.
Learning Point: Pupils can differentiate between evaporation, boiling, and sublimation.

Step 6: Relative Humidity and Dew Point

Time: 5 minutes
Teaching Skill: Explanation/Visual Aids
Teacher’s Activity: The teacher explains relative humidity and dew point using simple charts and daily weather examples. The teacher also briefly mentions how they are determined.
Pupils’ Activity: Pupils observe the charts, ask questions, and relate the concepts to weather phenomena.
Learning Point: Pupils understand the meanings of relative humidity and dew point.

Step 7: Evaluation/Review

Time: 5 minutes
Teaching Skill: Questioning/Assessment
Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

Define latent heat.
State the formula for calculating specific latent heat of vaporization.
Differentiate between evaporation and boiling.
What is dew point?
Calculate the heat required to melt 1 kg of ice at 0°C if its specific latent heat of fusion is 3.34 x 10⁵ J/kg.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 2 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key concepts of latent heat, changes of state, relative humidity, and dew point, emphasizing their practical relevance. The teacher assigns homework.
Pupils’ Activity: Pupils listen to the summary and copy down the homework.
Learning Point: Pupils reinforce their understanding and prepare for further study.

Lesson Keywords

Latent Heat – Heat absorbed or released during a phase change without temperature change.
Fusion – The process of melting.
Vaporization – The process of turning into a gas.
Evaporation – Liquid to gas below boiling point, surface phenomenon.
Boiling – Rapid liquid to gas at boiling point, throughout the liquid.
Sublimation – Solid to gas directly.
Relative Humidity – Ratio of actual to saturated water vapour pressure.
Dew Point – Temperature at which condensation begins.

Differentiation

For struggling learners, the teacher will provide simplified definitions and more guided practice with calculations. Advanced learners will be encouraged to research real-world applications of latent heat in industrial processes or climate science.

Note for teachers using this lesson plan

Ensure that laboratory equipment is available and functional for demonstration, or clearly explain the experimental setup if a full practical session is not feasible. Emphasize the distinction between heat capacity and latent heat. Encourage pupils to relate the concepts to everyday observations like sweating and cloud formation.