Class: Senior Secondary School 1 (SS1 / SSS 1)
Term: 2nd Term
Week: 2
Age: 15 years
Duration: 45 minutes
Subject: Radio, TV & Electronics
Curriculum Theme: Trade
Previous Lesson: Meaning Of Electronics And Electronic Circuit: Definitions.
Topic: CONCEPT OF EMISSION
Subject Matter: Definition of emission, Types of emission

Specific Objectives

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

Cognitive Domain:

Define the term ’emission’.
Identify and list different types of electron emission.
Describe the basic principle behind each type of emission.

Affective Domain:

Appreciate the importance of various emission types in electronic devices.
Show interest in further learning about electronic components that use emission.

Psychomotor Domain:

Draw simple diagrams illustrating an emission type, such as thermionic emission.
Distinguish between different emission types based on their causes.

Discuss with peers the applications of emission in everyday electronic gadgets.
Collaborate in identifying electronic devices that rely on specific emission principles.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Senior Secondary Schools.
State Unified Scheme of Work for Radio, TV & Electronics (SSS 1).
Akinwumi, T. (2018). Basic Electronics for Senior Secondary Schools. Ibadan: Spectrum Books.

Instructional Materials

The teacher will teach this lesson with the aid of:

An emission diagram.
A cathode ray tube image.
Whiteboard and markers.
Charts illustrating different emission types.

Rationale for the Lesson

This lesson helps pupils understand how electrons are released from materials, which is a fundamental concept in electronics. Understanding emission is essential for grasping the operation of many electronic components and devices, from vacuum tubes to modern display technologies, making it relevant to their daily experiences with technology.

Prerequisite/Previous Knowledge

Pupils have a basic understanding of atoms, electrons, and electricity.

Lesson Content/Board Summary

CONCEPT OF EMISSION

Definition of Emission

Emission is the process by which electrons are released or ejected from the surface of a material, typically a metal, into a vacuum or a gas. This release of electrons requires an external energy source to overcome the forces holding the electrons within the material.

Types of Emission

There are several types of electron emission, each caused by a different form of energy supplied to the material:

Thermionic Emission: This occurs when electrons are emitted from a heated metal surface. The heat energy provided is sufficient to overcome the work function of the metal, causing electrons to gain enough kinetic energy to escape. Examples include vacuum tubes and cathode ray tubes (CRTs).
Photoelectric Emission: This is the emission of electrons from a material when light of a suitable frequency shines on its surface. The energy from the photons of light is absorbed by the electrons, enabling them to escape. Examples include solar cells, phototubes, and image sensors.
Secondary Emission: This type of emission occurs when high-energy primary electrons strike a material surface, causing the ejection of other electrons (secondary electrons) from that surface. This phenomenon is used in electron multipliers and photomultiplier tubes.
Field Emission (or Cold Emission): This is the emission of electrons from a metal surface due to the application of a strong external electric field. The intense electric field pulls electrons out of the metal even at room temperature. It is utilized in field emission displays and electron microscopes.

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, reviews the previous lesson briefly, and then introduces the new topic, “Concept of Emission,” by asking pupils if they know how light is produced in old television sets or how solar panels generate electricity. This leads to the idea of electrons being released.
Pupils’ Activity: Pupils respond to questions and listen attentively.
Learning Point: Pupils are introduced to the topic and relate it to prior knowledge or everyday observations.

Step 2: Definition of Emission

Time: 7 minutes
Teaching Skill: Explanation/Definition
Teacher’s Activity: The teacher defines “emission” as the process of electrons being released from a material surface, emphasizing the need for an energy source. The teacher writes the definition on the board.
Pupils’ Activity: Pupils listen, take notes, and ask questions for clarification.
Learning Point: Pupils understand the fundamental definition of emission.

Step 3: Thermionic Emission

Time: 8 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher explains thermionic emission, using the provided emission diagram or by drawing a simple diagram of a heated cathode. The teacher clarifies how heat energy causes electron escape and gives examples like old TV tubes.
Pupils’ Activity: Pupils observe the diagrams, listen to the explanation, and copy notes from the board.
Learning Point: Pupils learn about thermionic emission and its applications.

Step 4: Photoelectric Emission

Time: 7 minutes
Teaching Skill: Explanation/Illustration
Teacher’s Activity: The teacher explains photoelectric emission, highlighting the role of light energy. The teacher discusses examples such as solar panels and explains how light causes electrons to be ejected.
Pupils’ Activity: Pupils listen, take notes, and may ask questions about solar power.
Learning Point: Pupils understand photoelectric emission and its uses.

Step 5: Secondary Emission

Time: 6 minutes
Teaching Skill: Explanation
Teacher’s Activity: The teacher explains secondary emission, describing it as the emission of electrons caused by the impact of other high-energy electrons. The teacher gives examples where this is used.
Pupils’ Activity: Pupils pay attention and note down the key points.
Learning Point: Pupils learn about secondary emission and its mechanism.

Step 6: Field Emission

Time: 6 minutes
Teaching Skill: Explanation
Teacher’s Activity: The teacher explains field emission, focusing on how a strong electric field can pull electrons from a surface. The teacher mentions its use in advanced display technologies.
Pupils’ Activity: Pupils listen, compare it with other types, and complete their notes.
Learning Point: Pupils understand field emission and its applications.

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 emission in your own words.
Mention any three types of electron emission.
Explain thermionic emission.
What type of emission is utilized in solar panels?

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 1 minute
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the lesson by briefly reiterating the definition of emission and the four types discussed. The teacher assigns homework: “List one electronic device that uses each type of emission discussed today.”
Pupils’ Activity: Pupils listen to the summary and copy the homework.
Learning Point: Pupils consolidate their learning and prepare for further study.

Lesson Keywords

Emission – The process where electrons are released from a material.
Thermionic – Emission due to heat energy.
Photoelectric – Emission due to light energy.
Secondary – Emission due to impact by other electrons.
Field – Emission due to a strong electric field.
Cathode – The negative electrode from which electrons are emitted.
Anode – The positive electrode that attracts emitted electrons.

Differentiation

For pupils who are struggling, the teacher will provide simplified diagrams and allow more time for note-taking. Peer-to-peer explanation will be encouraged. For advanced pupils, the teacher will pose challenging questions about the quantum mechanical aspects of emission or ask them to research more complex applications of each emission type.

Note for teachers using this lesson plan

Ensure that the diagrams used are clear and simple to understand. Encourage pupils to relate the concepts to devices they encounter daily to make the lesson more engaging. Emphasize the energy conversion involved in each emission type. Practical demonstrations, if available and safe, would greatly enhance understanding.