Topic 11 - Static Electricity

• A material becomes negatively charged by gaining electrons
• Like charges repel
• opposite charges attract
• Lightning is caused by a difference in charge between bottom of cloud and ground, discharge seen as lightning
• A static charge is caused by a discharge due to a build of charge
• A negatively charged balloon induces a positive charge on the surface of the ball and attracts it to the wall
• Earthing a charged material neutralises it by charge flowing to or from earth
• a use of static electricity is fuelling cars or spray painting
•  Earthing is used to keep petrol refuelling safe by the Earth cable attached to fuel pipe to prevent a build of charge.
• an electric field is An area in which an electrically charged object will feel a force.
• The electric field around a positive point charge

  
• The electric field around a negative point charge.

  
• the uniform electric field between two oppositely charged parallel plates.

  
• electric field lines show the strength of the electric field by the closer together the lines are, the stronger the electric field.
• Static Charge

  An electric charge that builds up because of an imbalance between the number of electrons and protons
• Discharged


  To remove all excess static electric charge so that the object's charge is neutral
• Law of Electric Charges

  Charged objects can exert a push or pull on one another.
• Repulsion

  When two objects push each other away

  -Positively charged objects repel each other

  -Negatively charged objects repel

  -Objects with the same charge repel each other
• Attraction

  When two objects pull each other together

  -Positively charged objects will attract negatively charged objects

  -Charged objects will attract neutral objects
• Distance and amount of charge also affects force of charge

  -The greater the charge an object has the greater the force

  -The greater the distance between objects the less the force
• Protons have a ____________ charge.

  Positive
• Electrons have a ____________ charge.

  Negative
• Neutons have ____________ charge.

  No
• Protons and Neutons each have __________ the mass of an electron.

  2000x
• Charging by Friction

  -Occurs when 2 objects rub against one another

  -ex. walking across carpet, rubber in your shoes grabs some electrons from the carpet

  -When it occurs between 2 objects of different materials, electrons are transferred from one material to another

  -Protons never move

  
• Charging by Induction

  -Means charging a neutral object by bringing a charged object close to it

  -If a positively charged object is brought close to a neutral object, the electrons in the neutral object will move close to the positively charges object

  -If a negatively charged object is brought close, the electrons will move away

  -Does not say charged when object moves away

  -Amount of charge stays the same

  
• Charging by Conduction


  -Means charging a neutral object by touching it with a charged object

  -When neutral object is touched by charges object, electrons are transferred to the neutral object

  -Electrons move because the neutral object is first charged by induction and then the electrons are attracted to the positively charged object

  
• Insulator


  A material in which the electrons are bound tightly to the nucleus and are not free to move to other atoms

  -ex. plastic, glass, rubber, wood, oil fur
• Conductor


  A material in which the electrons are free to travel to neighbouring atoms

  -ex. metal (silver, copper, gold, aluminum, tungsten, nickel)
• Grounded


  A connection of an object to earth through a conductor
• earthing will remove the excess charge as electrons will move to cancel out the charge.
• Electrostatic spraying makes use of static electricity, the charged droplets spread out because they spray droplets as they pass
• Sparks can be dangerous, potentially igniting a fire.
• an electric field is the region where an electric charge experiences a force
• When lines of an electric field meet they produce a force. Like all forces this produces movement if the force is large enough to overcome the inertia of the charged particles.