Electrostatics Flashcards
A polythene rod is rubbed with a piece of wool and suspended from an insulating thread so that it is free to move. Another polythene rod is rubbed with a piece of wool and placed close to the suspended rod. The suspended rod is repelled. When a perspex rod is rubbed with a piece of wool it attracts the suspended polythene rod. Explain what experiments of this nature has shown concerning charge.
1) There are two types of charges.
2) Similarly charged objects repel each other.
3) objects that have unlike charges attract each other.
A polythene or ebonite rod is rubbed with a piece of wool and acquire a negative charge. Explain how this happens.
When the polythene rob was rubbed with the piece of wool:
1 ) electrons were transferred from the surface of the wool to the surface of the polythene rod.
2) The rod acquired a negative charge,
3) where as the wool acquired a positive charge, due to losing electrons.
4) In this process, charge is conserved.
A Perspex or glass rode acquires a positive charge when rubbed with wool. Explain how this happens.
When the glass or Perspex rod was rubbed with the piece of wool:
1) Electrons were transferred from the surface of the rod to the surface of the wool.
2) The rod acquired a positive charge.
3) And the wool having gained electrons, acquired a negative charge.
4) Charge is conserved, the electrons lost from the rod is gained by the wool.
How can you charge an uncharged object by induction? Explain using the insulated uncharged metal sphere.
1) A negatively charged rod is brought close to the uncharged metal sphere on the insulated support.
2) The negatively charged rod causes the electrons in the uncharged metal sphere to move to one side away from the rod.
3) The metal sphere is earthed by briefly touching it, removing electrons.
4) The rod is taken away and the metal sphere has become positively charged.
Explain why metals are good conductors of electricity. Give some examples of conductors.
In a metal,
1) the electrons that orbit the nucleus are situated in ‘shells.
2) The electrons in the innermost shells are held tightly by the nucleus.
3) In the outermost shells, the electrons are held less tightly by the nucleus.
4) These electrons are able to escape the electrostatic force of attraction of the nucleus.
5) The electrons are free to move throughout the metal structure and are said to be delocalised.
6) Electrons are charged and movement of charges constitutes an electric current.
7) Because of the high concentration of free, mobile electrons, metals are excellent conductors of electricity.
Examples: Copper, silver, iron, graphite (non-metal)
Explain why insulators are poor conductors of electricity. Give some examples of insulators.
In insulators, 1) The type of bonding is different from that of a metal. The electrons are tightly held in the bonds throughout the structure.
2) The means that there are no free mobile electrons to allow for electrical conduction.
3) Plastic and rubber are good insulators.
What are semiconductors?
Materials that are neither good conductors nor good insulators are called semiconductors.
