Class: Senior Secondary School 1 (SS1, SS 1, SSS1, SSS 1)
Term: Second Term
Week: 3
Age: 15 years
Duration: 45 minutes
Subject: Basic Electronics
Curriculum Theme: Basic Electronics
Previous Lesson: Electric Power: Relationship Between P, I and V.
Topic: ELECTRIC POWER Deriving power for electric power, and calculation of power in given circuits.
Subject Matter: deriving power formulae from P equals I V, power formula using I squared R, power formula using V squared over R, units of electric power, power calculations in given circuits

Specific Objectives

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

Cognitive Domain:

Define electric power.
State the standard unit of electric power.
Derive the formulas for electric power (P = IV, P = I²R, P = V²/R).
Calculate electric power in simple circuits using the appropriate formulas.

Affective Domain:

Appreciate the importance of understanding electric power in daily life.
Show interest in solving problems related to electric power.

Psychomotor Domain:

Use a calculator effectively to solve power calculation problems.
Apply the derived power formulas to practical circuit examples.

Collaborate with peers to solve power calculation problems.

Reference Materials

The following resources were used in planning this lesson:

Senior Secondary Education Curriculum for Basic Electronics.
State Unified Scheme of Work for Senior Secondary Schools.
Basic Electronics for Senior Secondary Schools, Book 1.
https://www.allaboutcircuits.com/textbook/direct-current/chpt-2/power-calculations/
https://www.khanacademy.org/science/physics/circuits-topic/circuits-resistance/v/power-in-circuits

Instructional Materials

The teacher will teach this lesson with the aid of:

Calculator
Charts showing power formulas
Circuit diagrams
Whiteboard and markers

Rationale for the Lesson

Understanding electric power helps pupils know how electrical devices consume energy and how to calculate this consumption. This knowledge is important for understanding household electricity bills and the efficiency of various electrical appliances they encounter daily.

Prerequisite/Previous Knowledge

Pupils have prior knowledge of electric current, voltage, and resistance, including Ohm’s Law.

Lesson Content/Board Summary

Electric Power

Definition of Electric Power

Electric power is the rate at which electrical energy is transferred by an electric circuit. It is the rate at which work is done or energy is consumed in an electrical circuit.

Units of Electric Power

The standard unit of electric power is the Watt (W). One Watt is defined as one Joule per second (1 W = 1 J/s). Larger units include kilowatt (kW) and megawatt (MW).

Derivation of Power Formulas

Electric power (P) can be expressed in different ways using Ohm’s Law (V = IR).

The fundamental formula for electric power is:

P = IV (Power = Current × Voltage)

Other formulas derived from P = IV and Ohm’s Law are:

P = I²R (Power = Current squared × Resistance): This is derived by substituting V = IR into P = IV, so P = I (IR) = I²R.
P = V²/R (Power = Voltage squared ÷ Resistance): This is derived by substituting I = V/R into P = IV, so P = (V/R) V = V²/R.

Calculations of Power in Electric Circuits

To calculate power, identify the known values (current, voltage, or resistance) and choose the appropriate formula.

Example 1: A bulb draws a current of 0.5 A when connected to a 12 V battery. Calculate the power consumed by the bulb.

Given: I = 0.5 A, V = 12 V
Formula: P = IV
Calculation: P = 0.5 A × 12 V = 6 W

Example 2: A heater has a resistance of 50 Ω and draws a current of 2 A. Calculate the power dissipated by the heater.

Given: I = 2 A, R = 50 Ω
Formula: P = I²R
Calculation: P = (2 A)² × 50 Ω = 4 A² × 50 Ω = 200 W

Example 3: An appliance is rated 240 V and has a resistance of 120 Ω. Calculate the power rating of the appliance.

Given: V = 240 V, R = 120 Ω
Formula: P = V²/R
Calculation: P = (240 V)² / 120 Ω = 57600 V² / 120 Ω = 480 W

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 what they understand by “power” in general terms. The teacher then relates this to electrical power by asking how they think electricity does work or consumes energy in their homes.
Pupils’ Activity: Pupils respond to questions and share their ideas about power and its relation to electricity.
Learning Point: Pupils are introduced to the concept of electric power and its relevance.

Step 2: Definition and Units of Electric Power

Time: 7 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines electric power, explains that it is the rate of energy transfer, and states its standard unit (Watt). The teacher uses charts to show the definition and units.
Pupils’ Activity: Pupils listen, take notes, and ask questions for clarification.
Learning Point: Pupils learn the definition and units of electric power.

Step 3: Derivation of P = IV

Time: 7 minutes
Teaching Skill: Derivation/Explanation
Teacher’s Activity: The teacher guides pupils through the derivation of the power formula P = IV, explaining the relationship between power, current, and voltage. The teacher writes the derivation clearly on the board.
Pupils’ Activity: Pupils follow the derivation, ask questions, and copy notes into their exercise books.
Learning Point: Pupils understand how P = IV is derived.

Step 4: Derivation of P = I²R

Time: 7 minutes
Teaching Skill: Derivation/Problem Solving
Teacher’s Activity: The teacher demonstrates how to derive P = I²R by substituting Ohm’s Law (V = IR) into P = IV. An example calculation using this formula is worked on the board.
Pupils’ Activity: Pupils pay attention to the derivation and the example, taking notes and attempting to solve the example.
Learning Point: Pupils learn to derive and apply the formula P = I²R.

Step 5: Derivation of P = V²/R

Time: 7 minutes
Teaching Skill: Derivation/Problem Solving
Teacher’s Activity: The teacher shows how to derive P = V²/R by substituting Ohm’s Law (I = V/R) into P = IV. Another example calculation using this formula is worked on the board.
Pupils’ Activity: Pupils observe the derivation and example, participating in the discussion and copying notes.
Learning Point: Pupils learn to derive and apply the formula P = V²/R.

Step 6: Worked Examples and Practice

Time: 7 minutes
Teaching Skill: Application/Practice
Teacher’s Activity: The teacher provides additional circuit diagrams and problems, guiding pupils to choose the correct power formula and solve them. The teacher encourages pupils to work in pairs.
Pupils’ Activity: Pupils work collaboratively to solve the practice problems using calculators and the derived formulas. They present their solutions.
Learning Point: Pupils gain practical experience in calculating electric power.

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.
State the S.I. unit of electric power.
Derive the formula P = I²R starting from P = IV and Ohm’s Law.
A resistor of 10 Ω carries a current of 3 A. Calculate the power dissipated.

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 points of the lesson, emphasizing the importance of electric power in understanding electrical circuits and devices. The teacher gives pupils homework to practice more power calculations.
Pupils’ Activity: Pupils listen to the summary and copy down the homework.
Learning Point: Pupils consolidate their learning and are assigned further practice.

Lesson Keywords

Power – The rate at which electrical energy is transferred or consumed.
Current – The flow of electric charge.
Voltage – The electric potential difference between two points.
Resistance – The opposition to the flow of electric current.
Watt – The S.I. unit of power.
Ohm’s Law – States that V = IR.

Differentiation

For pupils who are struggling, the teacher will provide simpler problems with fewer steps and offer one-on-one support. For advanced pupils, the teacher will provide more complex problems involving multiple components or ask them to research real-world applications of power calculations, such as energy efficiency ratings of appliances.

Note for teachers using this lesson plan

Ensure pupils have a solid grasp of Ohm’s Law before this lesson. Emphasize the units for each quantity and the importance of using the correct formula based on the given information. Encourage pupils to show all their working steps during calculations.