PHYSICS NOTES FOR FORM TWO TOPIC 1:STATIC ELECTRICITY

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 PHYSICS NOTES FOR FORM TWO TOPIC 1:STATIC ELECTRICITY

Concept of Static Electricity

The Concept of Static Electricity
Explain the concept of static electricity
Static electricity refers to the electric charges stored on a conductor.

 

The Orign of Charges

Explain the origin of charges
When a plastic pen is rubbed with a cloth, it acquires the property of attracting small bits of paper or light objects. In this case, the plastic pen is said to be electrified.
Electrification by rubbing was observed a long time ago by ancient Greeks. After the discovery of electricity, things were grouped into two groups, electrics and non-electrics. Electrics refer to things which are readily electrified while non-electrics are reverse of the former.

The two Types of Charges

Identify the two types of charges
There are two types of charge:
  1. positive charge
  2. negative charge
Identification of charge
Suspend a polythene rod A rubbed with fur. Bring another polythene rod B rubbed with fur up to the rod A. Take a plastic rod and rub it with fur. Bring the plastic rod to up to the suspended rod A. Repeat the exercise with acetate and glass rod rubbed with silk cloth.

Observation

An electrified polythene rod repels another electrified polythene rod. An acetate rod rubbed with silk repels another acetate rod rubbed with silk cloth but it attracts a plastic rod rubbed with fur.

 

Explanation

Polythene and plastic when rubbed with fur becomes electrified with the same kind of electricity known as negative electricity (charge).
Acetate and glass when rubbed with silk cloth becomes electrified with the same kind of electricity called positive electricity(charge).
Charging is the process of electrifying a body.
A positively charged body carries positive charges and a negatively charged body carries negative charges.The symbols used for positive and negative charges are + and – respectively.

The Fundamental Law of Static Electricity

State the fundamental law of static electricity
The Fundamental law of electrostatic charges states that:“Like charges repel each other while unlike charges attract each other”
Charging Bodies Using Different Methods
Charge bodies using different methods
In order to understand the process of charging we have to understand the structure of bodies or things. All bodies are made up of extremely small, indestructible bits of matter called atoms.
An atom consists of a nucleus surrounded by electrons. The nucleus consists of proton and neutron.The protons are positively charged while electrons are negatively charged and the neutrons are neutral.
The whole atom is electrically neutral because it contain equal number of protons and electrons.
The following are the methods of charging;
  1. Rubbing
  2. Induction
  3. Contact
Charging by rubbing
A polythene rod rubbed with fur becomes negatively charged.Rubbing results in the transfer of electrons from fur to the polythene rod.
Fur becomes positively charged because some of its electrons are transferred to the polythene rod.The polythene gains excess electrons and hence it becomes negatively charged.
Note:It is only the electrons in matter which can be transferred by rubbing.
Charging by induction
A charged polythene rod is held near uncharged copper rod suspended from a cotton thread.
The electrons of the copper rod are repelled by the negatively charged polythene rod.Hence the electrons move to the far side of the copper leaving behind a net positive charge on the side facing the polythene rod.
Touch the copper rod with your finger when the charged rod is still in position. The electrons from copper rod flow through your body to the earth. Leaving it with a net positive charge. Remove the finger from the copper rod and finally remove the charged polythene rod.
The rod has therefore been positively charged by electrostatic induction.The charges that appear on the copper rod are called induced charges.
Charging by contact
A charged body (eg; positively charged metal can) is brought in contact with uncharged body B.

Lightning Conductor

The Phenomenon of Lightning Conductor
Explain the phenomenon of lightning conductor
Lightning is a gigantic electric spark discharge occurring between two charged clouds or between a cloud and the earth.
Ligthning conductor is a long pointed iron rod with its lower end buried in the earth and the other above the highest part of the building which is used to protect the building from lightning damage.
The Structure and Mode of Action of Lightning Conductor
Describe the structure and mode of action of lightning conductor
Structure of a lightning conductor
It consists of a long thick pointed copper rod with its lower end buried in the earth(earth plate) and the other end reaching above the highest part of the building and ending in several sharp spikes. -It is fixed to the side of the building.

Mode of action of lightning conductor
When a negatively charged thunder-cloudpasses overhead it acts inductively on the conductor,charging the points positively and the earth plate negatively.
The negative charge on the plate is, of course, immediately dissipated into the surrounding earth. At the same time point action occurs at the spikes. Negative ions are attracted to the spikes and becomes discharged by giving up their electrons. These electrons then pass down the conductor and escape to earth.
At the same time positive ions are repelled upwards from the spikes and spread out to form what is called a space charge. This positive space charge, however, has a negligible effect in neutralizing the negative charge on the cloud.
Note:Without the protection of a lightning conductor the lightning usually strikes the highest point, generally a chimney, and the current passes to earth through the path of least resistance. Considerable heat is generated by the passage of the current and sometimes it may set into fire.

A Simple Lighting Conductor

Construct a simple lightning conductor
A simple lightning conductor

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