Electric Charge (OCR GCSE Combined Science A (Gateway): Physics): Revision Note

Electric Charge

• 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 an acetate rod being charged by rubbing it with a cloth

  • Both the rod and cloth are insulating materials

• 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 they have equal numbers of negative charges (electrons) and positive charges

• 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