Static Electricity

• Charging by friction


  When certain insulating materials are rubbed against each other they become electrically charged
• Charging by friction


  1. Charges remain on the insulators and cannot immediately flow away

  2. One becomes positive and the other negative
• Charging by friction


  • A plastic or polythene rod being charged by rubbing it with a cloth
• Charging by friction


  • Negatively charged electrons are transferred from one material to the other
  • The material loses electrons
  • The material becomes positively charged
  • The other material gains electrons and becomes negatively charged
• Charge of a particle

  • Positive
  • Negative
  • Neutral (no charge)
• Electrons, protons, neutrons


  • Electrons are negatively charged
  • Protons are positive
  • Neutrons are neutral
• Neutral atom


  • The number of electrons is equal to the number of protons
  • The equal (but opposite) charges cancel out to make the overall charge of the atom zero
• Charged object


  • Becomes negatively charged when it gains electrons
  • Becomes positively charged when it loses electrons
• Force between two charged particles/objects


  • Attractive (the objects get closer together)
  • Repulsive (the objects move further apart)
• Attractive/repulsive force


  • Depends on the charges of the two objects
  • If the charges are opposite, they will attract
  • If the charges are the same, they will repel
• Static electricity


  The stationary electric charge which is produced by friction which causes sparks, or the attraction of other small objects such as dust or hair
• Static electricity


  • Caused by the imbalance between negative and positive charges in two objects
  • Only works for insulators, since in conductors, the charge will move through them instead of remaining stationary
• Static electricity and sparking

  1. Produced by rubbing surfaces which causes insulators to become charged by friction

  2. Applies to solids, liquids and gases
• Electrically neutral


  Negative (electrons) and positive charges are evenly distributed
• Charge transfer


  1. One object becomes negatively charged and the other positively charged

  2. Difference in charges leads to a force of attraction between itself and other objects which are also electrically neutral, by attracting the opposite charge to the surface of the objects they are attracted to
• Examples of static electricity in everyday life


  • Dust and dirt attracted to TV screens and computer monitors
  • Dust build-up on the edges of a fan
  • Clothes clinging to each other after being in a tumble dryer, especially those made of synthetic fabrics
  • Hair sticking up after pulling a hat off
  • Combing dry hair with a plastic comb and the hair stays attracted to the comb
  • A child's hair sticking up after going down a plastic slide
  • Photocopiers use black powder to stick to white paper to create a copy of a document
• Sparking


  • The build-up of electrostatic charge can be quite dangerous and can cause sparking (also known as an electric shock)
  • A static electric spark occurs when two objects which are charged by friction and become oppositely charged and have a surplus of electrons so large that the electrons 'jump' across to an object that is neutral
  • Since a current is the flow of electrons, this causes a small current to flow between the objects, called a spark
• Sparks can become quite dangerous and can cause a fire by igniting flammable gases and liquids, such as petrol
• Charged object


  Creates an electric field around itself
• Magnets


  Create magnetic fields
• Electric field lines


  • Point away from positive charges and towards negative charges
• Electric fields are always directed away from positive charges and towards negative charges
• Strength of an electric field


  • Strongest close to the charged object (field lines closer together)
  • Weaker further away from the charged object (field lines further apart)
• Electric forces in a field

  Objects in an electric field will experience an electrostatic force
• Charges are the same (negative and negative or positive and positive)


  Force will be repulsive and the second charged object will move away from the charge creating the field
• Charges are opposite (negative and positive)


  Force will be attractive and the second charged object will move toward the charge creating the field
• Negative particle enters the electric field

  Feels a force of attraction towards the positive charge
• Size of the force


  • Stronger as the distance between the two charged objects decreases
  • Weaker as the distance between the two charged objects increases
• The relationship between the strength of the force and the distance applies to both the force of attraction and force of repulsion
• Two negative charges brought close together


  Have a stronger repulsive force than if they were far apart
• Electric field


  A region in which a charged object will experience an electric force
• Objects with static charge create an electric field in the space around them
• If other charges enter the field

  They will experience an electric force, attracting or repelling them from the object
• Electric field lines


  • Always in the direction of positive to negative
• Electric field lines for a charged, isolated sphere


  • Point away from the centre of a positive sphere
  • Point towards the centre of a negative sphere
• Uniform electric field (between two parallel plates)


  • Straight parallel lines from positive to negative
• Electric field pattern between two oppositely charged spheres (or point charges)


  • Slightly different and looks like
• The electric field helps to explain the non-contact force between charged objects
• The electric field cannot be seen, but can be detected by another charged object that moves within that field due to the electric force
• This is a non-contact force because the charged objects do not touch for the force to be exerted