static and charge

• when two objects are rubbed together, friction causes electrons to move from one object to another, this can lead to a build up of charge.

  however, this doesn't work for friction between two conducting materials because the electrons would just flow straight out.
• when two materials are rubbed together, electrons are transferred
• a large build up of charge can cause a large potential difference between the object and the earth.

  the large potential difference could allow electrons to jump through the air, causing a spark.
• all charged objects have an electric field
• field lines always point from positive to negative charge.
•  Electric fields are strongest when close to the charged particle, and get weaker further away from the charged particle.
• current: measure of flow of electrons [around the circuit]
• potential difference: force driving the flow of electrons around the circuit
• when two conductors are rubbed together

  the electrons will flow back into or out of them, so they stay neutral.
• when two insulators are rubbed together

  electron's can't flow, so a positive static charge is left on the object that lost electrons and a negative static charge on the object that gained electrons.
• polythene rod


  electrons move from the other material to the rod.
• acetate rod


  electrons move from the rod to the other material.
• electronically charged objects exert a force on one another. these forces get weaker the further apart the two objects are.
• force of electrostatic attraction: between two oppositely charged objects
• force of electrostatic repulsion: between two objects with like charges.
• electronically charged objects attract small neutral objects placed near them e.g. small scraps of paper.

  this happens because the charged rod induces a charge in the paper - if the rod is positively charged, it attracts the electrons in the paper towards to it. if it's negatively charged, it repels the electrons. this gives the surface of the paper near the rod an opposite charge to the rod, so the rod and the paper are attracted together.
• electric fields


  go from positive to negative. the closer together the field lines are, the stronger the field, and the stronger the force a charged object in the field experiences.
• electric field cause electrostatic forces

  when the electric fields around two charged objects interact, a force is produced.
• potential difference: the driving force that pushes the current around.
• explain what would happen to the field lines if the charges were free to move.

  the field lines would straighten and shorten as the charges move together.