Electric Fields

Overview

• An electric field is a region of space in which an electric charge will experience a force.
• A charged object can affect other objects, both charged and uncharged, without actually touching them.
  • For example, a charged plastic rod can exert a force on another charged rod placed close by.

Representing an electric field

• A charged object is surrounded by an electric field. If a charged object moves into the electric field of a charged object, it will experience a force (either being attracted or repelled).
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  • The lines of force are shown coming out of a positive charge and going into a negative charge. This is because the lines indicate the direction of the force on a positive charge placed in the field.
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What is electric charge?

• In order to answer this question, you will need to answer it by explaining how objects behave when they have it (energy/charge).
• Since electric charge is a fundamental property of matter, it’s better to get a feel of it instead of having a clear definition.
• The electric force between two charged objects is one of the fundamental forces of nature. (The force of gravity between two masses is another fundamental force.)
  • The electric force holds together the particles that make up an atom. It holds atoms together to make molecules, and it holds molecules together to make solid objects.
• Whenever you stand on the floor, it is the electric force between molecules that prevents you from falling through the floor. Electric force is a very crucial force.
• Electric charge is a property of the particles that make up atoms.

Charged particles

• Remember that electrons are the negatively charged particles that are transferred from one object to another due to friction.
  • Also remember that they are smaller than an atom, and is only weakly attached to the outside of the atom.
• Remember that electric charge is a property of the particles that make up atoms.
• Charge is measured in coulombs (C), the SI unit for electric charge.
  • It has been discovered that the force between two charged objects depends on how big their charges are and on how far apart they are.
• Electrons are held by the attraction of the positively charged nucleus of the atom. The nucleus is positively charged because it contains positively charged protons.
  • Protons are positively charged particles found in the atomic nucleus.
• An electron has a very tiny amount of electric charge. The electron charge is extremely small:
  • electron charge = $-0.00000000000000000016C$ or $-1.6\times 10^{-19}C$
• A proton has exactly the same size of charge as an electron, but positive. This is the proton charge:
  • proton charge = $+0.00000000000000000016C$ or $-1.6\times 10^{-19}C$