static electricity and electric fields

• build-up of static is caused by...

  friction
• what happens when certain insulating materials are rubbed together?

  negatively charged electrons will be scaped off one and transferred on the other, leaving one with a positive static charge and another with an equal negative static charge
• which way the electrons are transferred depends on...


  the two materials involved
• what happened when a polythene rod is rubbed with a cloth duster?

  electrons move from the duster to the rod, making the rod negatively charged and the cloth positively charged
• what happened when a acetate rod is rubbed with a cloth duster?

  electrons move from the rod to the duster, making the rod positively charged and the cloth negatively charged
• true or false: both positive and negative charges move

  false: only electrons move, never positive charges
• too much static causes...

  sparks
• what happens as electric charge builds on an object?

  potential difference between the object and the earth (which is at 0V) increases
• static electricity


  the build up of charges on an object.
• what happens if the potential difference between the object and the earth gets large enough?

  electrons can jump across the gap between the charged object and the earth - this is the spark
• electrons can jump to any...

  earthed conductor that is nearby
• earthed conductor


  wire connected to the ground, which carries a potential of zero volts
• how are static shocks caused when getting out of a car?

  a charge builds up on the car's metal frame and when you touch the car, the charge traves through you to earth - this usually happens when the gap is fairly small
• what happens when two things with the same electric charge are bought close together?


  they will repel each other
• what happens when two things with opposite electric charge are bought close together?


  they will attract each other
• forces get ... the further apart the two things are

  weaker
• electrostatic attraction


  the non-contact force of attraction between opposite electric charges that draws them together
• electrostatic repulsion


  describes a force between particles with the same electrical charges that causes them to push apart from one another
• electric charged create...


  an electric field
• an electric field is created around...

  any electrically charged object
• electric field


  a region around a charged object where the object's electric force is exerted on other charged objects
• the closer to the object with an electric field you get...


  the stronger the field is
• electric field diagram


  - electric field lines go from positive to negative

  - they're always at a right angle to the surface

  - the closer the lines are, the stronger the field is: you can see that the further from the charge you go, the further apart the lines are and so the weaker the field is

  
• charged objects in an electric field feel a...

  force
• what does the force that is felt by charged objects in an electric field cause?

  attraction or repulsion
• what does is the force that is felt by charged objects in an electric field caused by?

  electric fields of each charged object interacting with each other
• the force on an object is linked to...

  the strength of the electric field it is in
• as you increase the distance between charged objects...

  the strength of the field decreases and the force between them gets smaller
• sparking can be explained by...

  electric fields
• sparks are caused when...

  there is a high enough potential difference between a charged object and the each (or an earthed object)
• a high potential difference causes...

  a strong electric field between the charged object and the earthed object
• the strong electric field causes electrons in the air particles to be...

  removed (known as ionisation)
• air is normally an insulator but when it is ionised it is...

  much more conductive so a current can flow through it - this is the spark
• how does the presence of a strong electric field cause a spark?

  the electric field would ionise air particles and allow charge to flow to the ground in the form of a spark
• ionisation


  the removal of one or more electrons from an atom, making the atom charged