1. Static Electricity Flashcards
Electric Charge (q)
Definition
Electric charge is a physical property of matter that causes it to experience an electric force when placed in an electric field.
Unit: coulomb (C)
Like charges repel and unlike charges attract
Each proton or electron has the same amount of charge of 1.6 x 10-19C
2 Factors affecting the electric force between 2 point charges
Electric force increases when:
1. Magnitude of the charges increases
2. Distance between the charges decreases
Conservation of Electric Charge
The conservation of electric charge states that electric charge cannot be created nor destroyed. It is only transferred from one object to another.
The total electric charge of an isolated system stays constant.
Electric Field
Definition
Electric field is a region in which an electric charge experiences an electric force.
Describe how electrical insulators are charged by friction
Assume A becomes positive and B becomes negative
When rubbed together, some of the electrons from A are removed from their atoms and are transferred to B.
B now has an excess of electrons and becomes negatively charged.
A now has a deficit of electrons and becomes positively charged.
Describe how electrical conductors are charged by contact
For A being positive/negative while B being neutral
If A is positive and B is neutral:
When A touches B, free moving electrons from B flow to A because unlike charges attract.
B now has a deficit of electrons and becomes positively charged.
If A is negative and B is neutral:
When A touches B, excess free moving electrons from A flow to B because like charges repel.
B now has an excess of electrons and becomes negatively charged.
Describe how electrical conductors are charged by induction
For A being neutral while B being positive/negative
If A is neutral and B is negative:
As like charges repel, free moving electrons in A are repelled to the side of A furthest from B.
This induces a positive charge at the side of A nearest to B.
If A is neutral and B is positive:
As unlike charges attract, free moving electrons in A are attracted to the side of A nearest to B.
This induces a negative charge at the side of A nearest to B.
Describe how a charged object is earthed
Both positive & negative
If the object is positive:
The flow of electrons from the Earth neutralises the excess positive charges on the object.
If the object is negative:
The excess free moving electrons on the object flow to the Earth and the object is neutralised.
Describe how neutral insulators are attracted to a charged object
For A being neutral insulator while B being positive/negative
If A is neutral and B is positive:
The electrons in A are attracted to B as unlike charges attract, and tend to move towards B within their molecules.
Since the electrons in A are nearer to B than its positive charges, the force of attraction is greater than the force of repulsion.
As a whole, A is attracted to B.
If A is neutral and B is negative:
The electrons in A are repelled by B as like charges repel, and tend to move away from B within their molecules.
Since the electrons in A are further from B than its positive charges, the force of attraction is greater than the force of repulsion.
As a whole, A is attracted to B.
How are electrical insulators and conductors discharged?
- By heating (for insulators)
- Heating ionises the air around the charged object.
- By a humid environment (for insulators)
- In a humid environment, the moisture on the surfaces of the charged objects and in the air can conduct electricity
- By earthing (for conductors)
