Class: Senior Secondary School 1 (SS1, SS 1, SSS1, SSS 1)
Term: First Term
Week: 5
Age: 15 years
Duration: 45 minutes
Subject: Basic Electricity
Curriculum Theme: Basic Electricity
Previous Lesson: Electric Power: Meaning and P = VI.
Topic: ELECTRIC POWER
Subject Matter: alternative formulae for calculating electric power, calculation of power dissipated in circuits, relationship between power work and energy, calculation of electrical energy in kilowatt hour, verification of Joule’s law

Specific Objectives

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

Cognitive Domain:

Define electric power and state its S.I. unit.
State the alternative formulae for calculating electric power.
Explain the relationship between power, work, and energy.
State Joule’s law of heating.

Affective Domain:

Appreciate the importance of calculating electric power and energy in daily life.
Show interest in understanding how electrical appliances consume energy.

Psychomotor Domain:

Calculate power dissipated in simple electric circuits using appropriate formulae.
Calculate electrical energy consumed in kilowatt-hour (kWh).
Record observations from an experiment to verify Joule’s law.

Collaborate with peers during practical activities.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum (Physics for Senior Secondary Schools)
State Unified Scheme of Work for Senior Secondary Schools
Any standard Senior Secondary Physics Textbook (e.g., New School Physics by P.N. Okeke and M.W. Anyakoha)

Instructional Materials

The teacher will teach this lesson with the aid of:

Power supply
Resistors
Ammeter
Voltmeter
Stopwatch
Charts showing power and energy formulae

Rationale for the Lesson

This lesson helps pupils understand how electrical energy is consumed and measured. It enables them to calculate the power of various appliances and understand their electricity bills, which is important for managing energy use at home and in the community.

Prerequisite/Previous Knowledge

Pupils are assumed to have prior knowledge of basic electrical concepts such as current, voltage, resistance, and energy from previous lessons.

Lesson Content/Board Summary

ELECTRIC POWER

Definition of Electric Power

Electric power is the rate at which electrical energy is converted into other forms of energy (e.g., heat, light, mechanical energy) in an electric circuit. The S.I. unit of electric power is the Watt (W).

Alternative Formulae for Electric Power

Electric power (P) can be calculated using the following formulae:

P = VI (Power = Voltage × Current)
P = I²R (Power = Current² × Resistance)
P = V²/R (Power = Voltage² / Resistance)

Where:

P = Power in Watts (W)
V = Voltage in Volts (V)
I = Current in Amperes (A)
R = Resistance in Ohms (Ω)

Calculation of Power Dissipated in Circuits

Power dissipated in a circuit or a component means the rate at which electrical energy is converted into heat or other forms of energy by that component. Calculations involve applying the appropriate power formula based on the given values of voltage, current, and resistance.

Relationship Between Power, Work, and Energy

Power is the rate at which work is done or energy is transferred.

Power = Work Done / Time taken (P = W/t)
Power = Energy Transferred / Time taken (P = E/t)

Therefore, Energy (E) = Power (P) × Time (t).

Calculation of Electrical Energy in Kilowatt-hour (kWh)

The S.I. unit of energy is the Joule (J), but for practical purposes, especially for electricity billing, electrical energy is measured in kilowatt-hour (kWh).

1 kilowatt-hour (kWh) is the energy consumed by a 1 kilowatt (1000 W) appliance operating for 1 hour.
1 kWh = 1000 W × 3600 seconds = 3,600,000 Joules (J).
To calculate energy in kWh: Energy (kWh) = Power (kW) × Time (hours).

Verification of Joule’s Law (Heating Effect of Current)

Joule’s Law states that the heat (H) produced in a conductor is directly proportional to the square of the current (I) flowing through it, the resistance (R) of the conductor, and the time (t) for which the current flows.

Mathematically, H = I²Rt.
The experiment involves passing current through a resistor immersed in water and measuring the rise in temperature over a specific time. By varying the current and measuring the heat produced, the law can be verified.

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 greets the pupils and asks them to recall the meaning of electric current, voltage, and resistance. The teacher then introduces the topic “Electric Power” by asking pupils about the power ratings of common household appliances.
Pupils’ Activity: Pupils respond to the questions and share their knowledge of appliance power ratings.
Learning Point: Pupils recall previous knowledge and are introduced to the lesson topic.

Step 2: Definition and Formulae of Electric Power

Time: 10 minutes
Teaching Skill: Explanation/Illustration
Teacher’s Activity: The teacher defines electric power, states its S.I. unit, and writes the alternative formulae (P=VI, P=I²R, P=V²/R) on the board. The teacher explains each term and its unit.
Pupils’ Activity: Pupils listen attentively, take notes, and ask questions for clarification.
Learning Point: Pupils learn the definition and formulae for electric power.

Step 3: Calculation of Power Dissipated in Circuits

Time: 8 minutes
Teaching Skill: Problem Solving/Demonstration
Teacher’s Activity: The teacher works through example problems on the board, demonstrating how to calculate power dissipated in a circuit using the different formulae, given various circuit parameters. For instance, calculate the power dissipated by a 10Ω resistor when a 2A current flows through it.
Pupils’ Activity: Pupils observe the examples, copy them into their notebooks, and attempt similar problems if given.
Learning Point: Pupils practice applying the power formulae to solve problems.

Step 4: Relationship Between Power, Work, and Energy

Time: 5 minutes
Teaching Skill: Explanation
Teacher’s Activity: The teacher explains the relationship between power, work, and energy, deriving the formula E = Pt. The teacher emphasizes that power is the rate of energy transfer.
Pupils’ Activity: Pupils listen, take notes, and understand the connection between these quantities.
Learning Point: Pupils understand that power is the rate of energy consumption or work done.

Step 5: Calculation of Electrical Energy in Kilowatt-hour (kWh)

Time: 7 minutes
Teaching Skill: Calculation/Application
Teacher’s Activity: The teacher explains why electrical energy is measured in kWh for practical purposes and demonstrates how to convert power in Watts to kilowatts and time in minutes/seconds to hours. The teacher provides an example calculation of energy consumed by an appliance over a period.
Pupils’ Activity: Pupils follow the explanation and practice converting units and calculating energy in kWh.
Learning Point: Pupils learn to calculate electrical energy in kilowatt-hour.

Step 6: Verification of Joule’s Law

Time: 5 minutes
Teaching Skill: Demonstration/Experimentation
Teacher’s Activity: The teacher explains Joule’s law and briefly outlines the experimental setup for its verification (using power supply, resistor, ammeter, voltmeter, stopwatch). If possible, the teacher performs a quick demonstration or shows a diagram/chart of the experiment, explaining how heat produced is related to I, R, and t.
Pupils’ Activity: Pupils observe the explanation or demonstration and understand the principle of Joule’s law.
Learning Point: Pupils understand the concept of Joule’s law and its experimental verification.

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 electric power and state its S.I. unit.
State any two alternative formulae for calculating electric power.
Explain the relationship between power and energy.
A heater has a power rating of 2000 W. Calculate the energy consumed in kWh if it operates for 3 hours.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 5 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the key points of the lesson, reiterating the definition of electric power, its formulae, and the calculation of energy. The teacher assigns homework which includes more practice problems on power and energy calculations.
Pupils’ Activity: Pupils listen to the summary and copy down the homework assignment.
Learning Point: Pupils consolidate their understanding of electric power and energy.

Lesson Keywords

Electric Power – The rate at which electrical energy is converted or transferred.
Watt (W) – The S.I. unit of power.
Kilowatt-hour (kWh) – A practical unit for measuring electrical energy, commonly used for billing.
Joule’s Law – States that heat generated in a conductor is proportional to I²Rt.
Dissipated Power – Electrical energy converted into heat or other forms in a component.

Differentiation

The teacher will provide additional support to struggling learners through guided practice and simplified examples. Advanced learners will be given more complex problems and encouraged to explore real-world applications of power and energy calculations.

Note for teachers using this lesson plan

Ensure that pupils understand the distinction between power and energy. Emphasize the units for each quantity and the importance of unit conversion, especially when calculating energy in kWh. Practical demonstrations, even simple ones, can significantly enhance understanding of concepts like Joule’s law.