Electric Charge (OCR Gateway GCSE Physics: Combined Science)

• When certain insulating materials are rubbed against each other they become electrically charged
  • This is called charging by friction

• The charges remain on the insulators and cannot immediately flow away
  • One becomes positive and the other negative

•  An example of this is a plastic or polythene rod being charged by rubbing it with a cloth
  • Both the rod and cloth are insulating materials

A polythene rod may be given a charge by rubbing it with a cloth

• This occurs because negatively charged electrons are transferred from one material to the other
• The material, in this case, the rod, loses electrons
• Since electrons are negatively charged, the rod becomes positively charged
  • As a result, the cloth has gained electrons and therefore is left with an equal negative charge

Charge & Electrons

• All objects are initially electrically neutral, meaning the negative (electrons) and positive charges are evenly distributed
• However, when the electrons are transferred through friction, one object becomes negatively charged and the other positively charged
  • The object to which the electrons are transferred becomes negatively charged
  • The object from which the electrons leave becomes positively charged

• This 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
• In the example below, when the cloth and rod are rubbed together, the electrons are transferred to the cloth and leave from the rod

Electrons are rubbed onto the cloth leaving the cloth negatively charged and the rod positively charged