Static electricity Flashcards
State the laws of electrostatics (2)
1) Two like charges repel each other
2) Two unlike charges attract each other
What happens when we earth a charged object?
Neutralisation process occurs. Electrons will move towards the charged object or towards the earth in order to neutralise the object.
How do we charge a body?
1) By direct contact (only to charge conductors)
2) By friction (to charge non-conductors)
3) By electrostatic induction (to charge conductors)
Describe the process of electrostatic induction
1) If we want to charge a conductor negatively, bring a positive metal rod near it.
2) Earth the metal sphere. The electrons will move up and neutralise the positive charges.
3) Remove the earth wire first.
4) Remove the metal rod. The negative charges are uniformly distributed
What is charge measured in?
Coulombs
Describe a conductor and give examples
A conductor is a body having large number of free electrons in its structure. It is more likely to give its outermost electrons. E.g. all metals, acids, grahite
Describe an insulator and give examples
An insulator is a body having no free electrons in its structure. It is more likely to accept electrons. E.g. glass, silk, wood
How are insulators charged by friction?
When an insulator is rubbed against another insulator there is a transfer of electrons from one body to another. If one gains electrons the other will lose electrons. One body becomes negatively charged and the other becomes positively charged
Describe 2 experiments to demonstrate charging by friction
1) Bring the negatively charged object near neutral pieces of paper lying on a table. The paper jumps and sticks to the negatively charged object. This is due to attraction by the negative charges.
2) Bring the negatively charged object close to a fine stream of water flowing from a tap. The negatively charged object attracts the neutral stream of water
What does the charging of solids involve?
The movement of elctrons
Define an electric field
A region in which an electric charge experiences a force
What are the directions of the electric field for negative and positive charges?
The are directed outwards for a positive charge and inwards for a negative charge
How do electric lines of force emerge and move?
They always emerge at 90º and move from positive to negative charge
