Class: Senior Secondary School 1 (SS1, SS 1, SSS1, SSS 1)
Term: 3rd Term
Week: 8
Age: 15 years
Duration: 45 minutes
Subject: Basic Electronics
Curriculum Theme: Basic Electronics
Previous Lesson: Electro-Magnetism: Applications and Simple Constructions.
Topic: Electric Emission
Subject Matter: Concepts of Thermionic Emission, Photoelectric Emission, Secondary Emission, and Field Emission; Examples of Devices Using Electron Emission.

Specific Objectives

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

Cognitive Domain:

Define electric emission.
Describe the four types of electron emission: thermionic, photoelectric, secondary, and field emission.
State examples of devices that use each type of electron emission.

Affective Domain:

Show interest in understanding how electron emission works in various electronic devices.
Appreciate the importance of electron emission in modern technology.

Psychomotor Domain:

Identify different types of electron emission from given descriptions.
Classify electronic devices based on the type of electron emission they utilize.

Participate actively in class discussions about electron emission concepts.
Collaborate with peers to clarify understanding of complex principles.

Reference Materials

The following resources were used in planning this lesson:

9 Years Basic Education Curriculum for Basic Technology
State Unified Scheme of Work for Basic Electronics (SSS 1)
Basic Electronics for Senior Secondary Schools by P.N. Okeke
https://nerdc.gov.ng/9-years-basic-education-curriculum/
https://www.education.gov.ng/schemes-of-work/

Instructional Materials

The teacher will teach this lesson with the aid of:

Pictures showing different types of electron emission (e.g., heated filament, light striking a surface, electron beam hitting a target).
Diagrams of devices that use electron emission (e.g., vacuum tube, photocell).

Rationale for the Lesson

Understanding electron emission is important for pupils to grasp the fundamental principles behind many electronic devices. It helps them to know how various technologies, from older television sets to modern sensors, operate by controlling the flow of electrons.

Prerequisite/Previous Knowledge

Pupils have basic knowledge of electricity, atomic structure, and the concept of electrons as charge carriers.

Lesson Content/Board Summary

ELECTRIC EMISSION

Concept of Electric Emission

Electric emission is the process by which electrons are released from the surface of a material, usually a metal, into a vacuum or a gas. This process requires energy to overcome the forces holding the electrons within the material.

Types of Electric Emission

There are four main types of electric emission, distinguished by the energy source used to free the electrons:

Thermionic Emission
Photoelectric Emission
Secondary Emission
Field Emission

Thermionic Emission

Thermionic emission is the process where electrons are emitted from a heated metal surface. When a metal is heated, the kinetic energy of its free electrons increases, allowing some to overcome the surface barrier and escape into the surrounding space.

Devices that use thermionic emission include:

Vacuum tubes (e.g., old radio valves, cathode ray tubes in older televisions and monitors).
Filaments in some electron guns.

Photoelectric Emission

Photoelectric emission is the release of electrons from a material when light (electromagnetic radiation) shines on its surface. The energy from the photons of light is absorbed by electrons, giving them enough energy to escape from the material.

Devices that use photoelectric emission include:

Photocells (light sensors).
Solar cells (photovoltaic cells).
Photomultiplier tubes.

Secondary Emission

Secondary emission occurs when high-energy primary electrons strike a material surface, causing other electrons (secondary electrons) to be emitted from that surface. The primary electrons transfer their energy to the surface electrons, dislodging them.

Devices that use secondary emission include:

Electron multipliers.
Photomultiplier tubes.
Scanning electron microscopes (SEM).

Field Emission

Field emission (also known as cold emission) is the emission of electrons from a material surface due to the presence of a strong external electric field. This strong field reduces the potential barrier at the surface, allowing electrons to tunnel out even at low temperatures.

Devices that use field emission include:

Field emission displays (FEDs).
Electron guns in some advanced cathode ray tubes.
Vacuum microelectronic devices.

Examples of Devices Using Electron Emission

Various electronic devices rely on the principles of electron emission for their operation. Some examples include:

Cathode Ray Tubes (CRTs) in old televisions and computer monitors.
X-ray tubes.
Electron microscopes.
Photocells and solar panels.
Vacuum tubes (diodes, triodes, etc.) used in older electronic circuits.

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 introduces the topic by asking them what they know about electrons and how they move in electrical circuits. The teacher then explains that electrons can also be made to leave the surface of materials, which is called electric emission.
Pupils’ Activity: Pupils respond to the teacher’s questions and listen attentively to the introduction.
Learning Point: Pupils are introduced to the concept of electron emission and its relevance.

Step 2: Presentation of Thermionic Emission

Time: 7 minutes
Teaching Skill: Explanation/Illustration
Teacher’s Activity: The teacher explains thermionic emission, defining it as the release of electrons from a heated surface. The teacher uses diagrams to illustrate how heating a metal increases the kinetic energy of electrons, allowing them to escape. Examples of devices like vacuum tubes are mentioned.
Pupils’ Activity: Pupils listen, take notes, and ask questions for clarification.
Learning Point: Pupils understand the concept of thermionic emission and identify devices that use it.

Step 3: Presentation of Photoelectric Emission

Time: 7 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher defines photoelectric emission, explaining how light energy can cause electrons to be emitted from a surface. The teacher may use a diagram of a photocell to show this process and mentions devices like solar cells.
Pupils’ Activity: Pupils observe the illustrations, listen to the explanation, and contribute to discussions.
Learning Point: Pupils understand photoelectric emission and can name devices that apply this principle.

Step 4: Presentation of Secondary Emission

Time: 7 minutes
Teaching Skill: Explanation/Comparison
Teacher’s Activity: The teacher explains secondary emission, describing it as the emission of electrons caused by the bombardment of a surface by other high-energy electrons. The teacher compares it to other types of emission and gives examples like electron multipliers.
Pupils’ Activity: Pupils listen, make comparisons, and note down key points.
Learning Point: Pupils grasp the concept of secondary emission and its applications.

Step 5: Presentation of Field Emission

Time: 7 minutes
Teaching Skill: Explanation/Questioning
Teacher’s Activity: The teacher explains field emission, detailing how a strong electric field can pull electrons from a material’s surface without heating it. The teacher discusses examples such as field emission displays.
Pupils’ Activity: Pupils listen, ask questions about the strong electric field, and understand the concept.
Learning Point: Pupils understand field emission and its role in modern technologies.

Step 6: Examples of Devices Using Electron Emission

Time: 5 minutes
Teaching Skill: Listing/Application
Teacher’s Activity: The teacher lists and briefly describes various electronic devices that utilize one or more forms of electron emission, consolidating the examples mentioned earlier.
Pupils’ Activity: Pupils listen and note down the examples of devices.
Learning Point: Pupils can identify various devices that depend on electron emission.

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 emission.
Mention two types of electron emission.
Explain thermionic emission.
State one device that uses photoelectric emission.

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 main points of the lesson, reiterating the four types of electron emission and their importance. The teacher assigns homework for pupils to research more devices that use electron emission.
Pupils’ Activity: Pupils listen to the summary and copy the homework assignment.
Learning Point: Pupils consolidate their learning and are encouraged to do further research.

Lesson Keywords

Electric Emission – The process by which electrons are released from a material surface.
Thermionic Emission – Electron emission due to heat.
Photoelectric Emission – Electron emission due to light.
Secondary Emission – Electron emission due to bombardment by other electrons.
Field Emission – Electron emission due to a strong electric field.

Differentiation

For pupils who grasp concepts quickly, the teacher will encourage them to research the practical applications of each emission type in detail. For pupils needing more support, the teacher will provide simplified diagrams and allow more time for questions and one-on-one explanations.

Note for teachers using this lesson plan

Teachers should ensure that pupils understand the fundamental concept of electrons overcoming a work function or energy barrier to be emitted. Practical examples or visual aids are important for making the abstract concepts relatable.