P3.1 Static Electricity

• What is static electricity?

  Build-up of charge on insulating materials
• Why do most materials have an overall neutral charge?

  Positive protons and negative electrons cancel out
• What happens when insulating materials are rubbed together?

  Electrons are transferred, causing charge build-up
• How do conducting materials behave when rubbed together?

  Electrons flow back, preventing charge build-up
• What happens to a polythene rod when rubbed with a cloth?

  It gains negative charge, cloth becomes positive
• What happens when an acetate rod is rubbed with a cloth?

  Acetate rod becomes positive, cloth becomes negative
• What determines the direction of electron transfer when materials are rubbed together?

  Specific materials involved in the interaction
• Why do positive static charges occur?

  Because an object has lost negative electrons
• What develops as an object gains more negative electrons?

  A potential difference between the object and earth
• What happens if the potential difference is large enough?

  Electrons can jump across the gap, causing a spark
• What is the potential of earth objects?

  Always at zero volts
• Can charges build up on conductors?

  Yes, but it's less common
• How can cars build up charge?

  Metal frame contacts wind, transferring electrons
• What happens when you touch a charged car?

  You may experience a small electric shock
• What are the key points about static electricity?

  • Build-up of charge on insulators
  • Charges cancel in neutral materials
  • Friction causes electron transfer
  • Conductors allow electrons to flow back
  • Positive charge from lost electrons
  • Potential difference leads to sparks
• What are the differences in charge behavior between conductors and insulators?

  • Conductors: Electrons flow back, no charge build-up
  • Insulators: Electrons can't flow back, charge builds up
• 1. All objects have positively charged protons and negatively charged electrons. 
  2. Normally, the number of protons and electrons are the same which means the object is neutral overall.
• When two objects are rubbed together, the friction can cause electrons to move from one object onto the other. This can lead to a build up of charge. 

  However, this doesn't work for friction between two conducting materials as the electrons would just flow straight back again.
• When two materials are rubbed together, which particles are transferred?

  Electrons
• A material which gains additional electrons will have a:


  Negative charge
• When two objects are rubbed together, electrons may be transferred. The object that becomes positive, must have ________ electrons.


  lost
• A large build up of charge on an object can cause a large potential difference between the object and the earth.

  The large potential difference could allow electrons to jump through the air to earth, causing a spark. 
• Objects normally have a neutral charge overall. Explain why.


  Objects consist of atoms, which consist of protons, neutrons, and electrons.

  Normally, the number of positive protons is equal to the number of negative electrons, so the number of negative electrons, so the overall charge is neutral.
• How does static electricity build up?


  When two objects are rubbed together, the friction can cause electrons to move from one object onto the other.

  This leads to a buildup of charge.
• Is static electricity more likely to build up on conductors or insulators?


  Static electricity will only build up on insulating materials, as the electrons would just flow straight back if the materials were conductors.
• When two materials are rubbed together, which particles are transferred?


  Electrons.
• What causes a spark between an object and the earth?

  A large build-up of charge on an object can cause a large potential difference between the object and the earth.

  The large potential difference could allow electrons to jump through the air from one object to the other. We call this jumping of electrons a spark.