Electric Charge, Types and the Law of Charges for SS 1

Class: SS 1
Term: First Term
Week: 4
Age: 15 years
Duration: 60 minutes
Subject: Physics
Curriculum Theme: Interaction of matter, space, and time
Focal competence: Producing, detecting, storing electric charges, and constructing metal spikes
Key competencies/values: Critical Thinking; Creativity and Innovation; Leadership; Innovation
Skills:

• Producing, detecting, and storing of electric charges
• Constructing metal spikes for protecting tall buildings from thunderstorms

Previous Lesson: Position, Distance and Displacement on the x-y Coordinate System
Topic: Electric Charge
Subject Matter: Meaning of the concept of electric charge

Specific Objectives

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

Cognitive Domain

• Define electric charge.
• State the electrostatic law.
• Identify types of charges on bodies.
• Describe earthing and metal spike construction.

Affective Domain

• Appreciate the importance of earthing and metal spikes for safety.
• Participate actively in group discussions on electric charge.

Psychomotor Domain

• Demonstrate how a body is charged by friction, induction, and contact.
• Generate electric charges.
• Store electric charges.
• Detect types of charges on bodies using an electroscope.
• Illustrate the concept of earthing.
• Construct a typical metal spike.

Social Domain

• Collaborate effectively in groups to detect and transfer charges.

Reference Materials

The following resources were used in planning this lesson:

• 2025 New Revised Senior Secondary Education Curriculum (SSEC)
• Relevant State Unified Scheme of Work
• New School Physics by M.W. Anyakoha
• The HeadTeacher Scheme of work For The New Revised Senior Secondary Education Curriculum (SSEC)

Instructional Materials

The teacher will teach this lesson with the aid of:

• Glass rod
• Plastic rod
• Fur
• Silky material
• Combs
• Pith ball electroscope
• Gold leaf electroscope
• Electrophorus
• Insulating stand
• Connecting wires
• Diagrams illustrating earthing and metal spike construction

Rationale for the Lesson

This lesson introduces students to the fundamental concept of electric charge, which is essential for understanding all electrical phenomena. It provides practical skills in generating, detecting, and storing charges, and highlights the crucial application of earthing and lightning conductors in protecting lives and property from electrical hazards.

Prerequisite/Previous Knowledge

Students should have a basic understanding of matter and its composition, including atoms and their subatomic particles (protons, neutrons, and electrons).

Lesson Content/Board Summary

Electric Charge

Meaning of Electric Charge

Electric charge is a fundamental property of matter that causes it to experience a force when placed in an electromagnetic field. It is associated with electrical attraction and repulsion. All matter is made up of atoms, which contain positively charged protons, negatively charged electrons, and neutral neutrons. An object becomes electrically charged when it gains or loses electrons.

Types of Electric Charges

There are two main types of electric charges:

1. Positive Charge: This occurs when an object loses electrons, resulting in a net excess of protons.
2. Negative Charge: This occurs when an object gains electrons, resulting in a net excess of electrons.

The Law of Electric Charges (Electrostatic Law)

The electrostatic law describes the interaction between charged bodies:

1. Like charges repel each other (e.g., positive repels positive, negative repels negative).
2. Unlike charges attract each other (e.g., positive attracts negative).

Methods of Producing Electric Charges

Electric charges can be produced on objects through various methods:

1. Charging by Friction (Rubbing): When two different insulating materials are rubbed together, electrons are transferred from one material to the other. The material that gains electrons becomes negatively charged, while the material that loses electrons becomes positively charged.

   Examples:

   1. Rubbing a glass rod with silk cloth makes the glass rod positively charged and the silk cloth negatively charged.
   2. Rubbing a plastic comb through dry hair makes the comb negatively charged and the hair positively charged.
2. Charging by Contact (Conduction): When a charged object touches an uncharged conductor, some of the charge is transferred to the uncharged object. Both objects end up with the same type of charge.

   Example: If a negatively charged rod touches a neutral metal sphere, electrons will transfer from the rod to the sphere, making the sphere negatively charged.

3. Charging by Induction: This method involves charging an object without direct contact with a charged body. When a charged object is brought near an uncharged conductor, it causes a redistribution of charges within the conductor. If the conductor is then earthed while the charged object is still nearby, it will acquire an opposite charge.

   Example: To charge a neutral metal sphere positively by induction:

   1. Bring a negatively charged rod close to (but not touching) the sphere. This repels electrons to the far side of the sphere, leaving the near side positively charged.
   2. Earth the sphere (e.g., by touching it with a finger) while the charged rod is still nearby. Electrons flow from the sphere to the earth.
   3. Remove the earth connection.
   4. Remove the charged rod. The sphere is now left with a net positive charge.

Detection of Electric Charges

Electric charges can be detected using devices such as:

1. Pith Ball Electroscope: A simple device consisting of a light pith ball suspended by an insulating thread. When a charged object is brought near it, the pith ball is attracted or repelled, indicating the presence of charge.
2. Gold Leaf Electroscope: A more sensitive device used to detect and identify the type of electric charge on a body. It consists of a metal cap connected to a metal rod, which has two thin gold leaves attached at its lower end, all enclosed in a glass case.

   Uses of a Gold Leaf Electroscope:

   1. To detect the presence of an electric charge.
   2. To determine the sign (positive or negative) of an electric charge.
   3. To compare the magnitudes of different charges.
   4. To demonstrate charging by induction and conduction.

Storage of Electric Charges

Electric charges can be stored using devices like:

1. Electrophorus: A simple device used to generate and store static electric charge by induction. It consists of a dielectric plate (e.g., ebonite or plastic) and a metal plate with an insulating handle.

   How an Electrophorus works:

   1. The dielectric plate is charged by friction (e.g., rubbing with fur).
   2. The metal plate is placed on the charged dielectric.
   3. The metal plate is briefly earthed (e.g., touched with a finger) while on the dielectric.
   4. The metal plate is lifted by its insulating handle, now carrying a charge opposite to that of the dielectric.
   5. This charge can then be transferred to another object or stored.
2. Capacitors: Electronic components designed to store electric charge and electrical energy in an electric field. (More advanced concept, briefly mention for context).

Earthing and Metal Spike Construction

Meaning of Earthing

Earthing (or grounding) is the process of connecting an electrical appliance or system to the earth (ground) using a conductor. This provides a safe path for excess electrical current to flow into the earth, preventing electric shock and damage to appliances. The earth acts as an infinite sink or source of electrons, capable of absorbing or supplying a large number of electrons without becoming significantly charged.

Advantages of Earthing:

1. Safety from Electric Shock: It protects users from electric shock by ensuring that if a live wire touches the metal casing of an appliance, the current flows to the earth instead of through the user.
2. Protection of Appliances: It prevents damage to electrical appliances from sudden surges of current.
3. Stabilisation of Voltage: It helps to maintain a stable voltage in the electrical system.

Metal Spike Construction (Lightning Conductor)

A metal spike, commonly known as a lightning conductor or lightning rod, is a metal rod mounted on top of a building and connected to the ground through a thick copper or aluminium wire. Its purpose is to protect buildings and structures from lightning strikes.

How a Metal Spike Works:

1. The sharp point of the spike ionises the air around it, creating a path for the lightning discharge.
2. If lightning strikes the building, it preferentially hits the metal spike.
3. The charge is then safely conducted through the thick wire directly into the earth, bypassing the building structure.

Advantages of Metal Spikes:

1. Protection from Lightning: It diverts the powerful electrical current of a lightning strike safely to the ground, preventing fire, structural damage, and injury to occupants.
2. Reduces Risk of Damage: Minimises the risk of damage to electrical systems and electronic equipment within the building.

Teaching Methods/Instructional Techniques

Discussion, Demonstration, Guided Practice, Question and Answer, Explanation, Group Work, Practical Activity

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Engaging/Questioning

Teacher’s Activity: The teacher greets the students and asks them to recall what happens when they rub a plastic comb through their dry hair and then bring it near small pieces of paper. The teacher then introduces the topic: Electric Charge.

Pupils’ Activity: Pupils respond by saying the paper pieces are attracted to the comb. They listen attentively to the introduction.

Learning Point: Introduction to electric charge

Step 2: Meaning and Types of Electric Charge

Time: 10 minutes

Teaching Skill: Explanation/Discussion

Teacher’s Activity: The teacher guides students in a group discussion on the meaning of electric charge, explaining that it is a fundamental property of matter. The teacher then explains the two types of charges (positive and negative) and the electrostatic law.

Pupils’ Activity: Pupils participate in the discussion, define electric charge, state the types of charges, and articulate the electrostatic law.

Learning Point: Definition and types of charge

Step 3: Production of Electric Charges

Time: 10 minutes

Teaching Skill: Demonstration/Explanation

Teacher’s Activity: The teacher demonstrates how a body is charged by friction (rubbing a glass rod with silk, and a plastic rod with fur), by contact (touching a charged rod to a neutral pith ball), and by induction (using a charged rod and an earthed conductor). The teacher explains the electron transfer in each method.

Pupils’ Activity: Pupils observe the demonstrations carefully and describe the processes of charging by friction, contact, and induction.

Learning Point: Methods of charging bodies

Step 4: Detection of Electric Charges

Time: 8 minutes

Teaching Skill: Demonstration/Guided Practice

Teacher’s Activity: The teacher demonstrates the use of a pith ball electroscope and a gold leaf electroscope to detect the presence and type of charge on a body. The teacher then guides students in groups to use an electroscope to detect charged bodies.

Pupils’ Activity: Pupils observe the demonstrations and then, in groups, use the electroscope to detect charges on various bodies.

Learning Point: Detecting electric charges

Step 5: Storage of Electric Charges

Time: 7 minutes

Teaching Skill: Demonstration/Guided Practice

Teacher’s Activity: The teacher demonstrates the use of an electrophorus to generate and transfer charges, showing how charges can be stored. The teacher then guides students to use an electrophorus to transfer and store charges.

Pupils’ Activity: Pupils observe the demonstration and then, in groups, use the electrophorus to generate and transfer charges.

Learning Point: Storing electric charges

Step 6: Earthing and Metal Spike Construction

Time: 10 minutes

Teaching Skill: Explanation/Illustration

Teacher’s Activity: The teacher explains the meaning and advantages of earthing, illustrating how it works with diagrams. The teacher also describes the construction of a metal spike (lightning conductor) and its function in protecting buildings from lightning strikes.

Pupils’ Activity: Pupils listen, ask questions, and describe the concepts of earthing and metal spike construction.

Learning Point: Earthing and lightning protection

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

1. What is electric charge?
2. State the law of electric charges.
3. Mention two ways a body can be charged.
4. How does a gold leaf electroscope work to detect charge?
5. Explain the importance of earthing in homes.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Understanding electric charge concepts

Step 8: Note-Taking

Time: 10 minutes

Teaching Skill: Guided Writing

Teacher’s Activity: The teacher guides pupils/students to copy the essential Board Summary notes on electric charge, its types, laws, production, detection, storage, earthing, and metal spikes into their notebooks.

Pupils’ Activity: Pupils/students copy the notes carefully into their notebooks.

Learning Point: Recording lesson notes

Step 9: Conclusion

Time: 5 minutes

Teaching Skill: Summarising

Teacher’s Activity: The teacher briefly summarises the main points of the lesson, reiterating the importance of understanding electric charges and their practical applications in safety (earthing and lightning conductors). The teacher encourages students to observe electrical safety around them.

Pupils’ Activity: Pupils listen and ask any final clarifying questions.

Learning Point: Consolidation of electric charge concepts

Continuous Assessment/Further Study

Type: Homework/Practice Exercise

Instruction: Answer the following questions in your Physics notebook.

1. Differentiate between charging by friction and charging by induction, giving one example for each.
2. Describe how you would use an electrophorus to transfer a negative charge to a neutral metal sphere.
3. Draw a simple diagram to illustrate how a metal spike protects a building from lightning.
4. Research and list three common household appliances that require earthing for safety.

Lesson Keywords

• Electric Charge – A fundamental property of matter that causes it to experience a force in an electromagnetic field.
• Positive Charge – An object having a net deficit of electrons.
• Negative Charge – An object having a net excess of electrons.
• Electrostatic Law – Like charges repel, unlike charges attract.
• Friction – Charging by rubbing two materials together.
• Induction – Charging an object without direct contact.
• Conduction – Charging by direct contact.
• Electroscope – A device used to detect and measure electric charge.
• Electrophorus – A device used to generate and store static electric charge by induction.
• Earthing – Connecting an electrical system to the earth for safety.
• Metal Spike – A lightning conductor that protects buildings from lightning strikes.

Differentiation

Support: Provide simplified diagrams and hands-on guidance for students struggling with the concepts of induction and earthing. Pair weaker students with stronger ones for group activities.
Extension: Challenge advanced students to research and explain the concept of electric fields and potential differences related to charge, or to design a more efficient lightning conductor system for a complex building structure.

Suggested Lesson Videos

For further understanding, search on YouTube for:

• electric charge types ss1 physics
• charging by friction induction contact physics
• gold leaf electroscope working physics
• earthing and lightning conductors physics