gravitational forces, fundamental forces (Sections 2.6 and 2.9)
free-body diagrams (Section 2.4)
Newton's second law: force and acceleration (Section 3.3)
motion with constant acceleration (Sections 4.1–4.4)
equilibrium (Section 2.4)
adding vectors; resolving a vector into components (Sections 2.2–2.3)
Master the Concepts
Coulomb's law gives the electric force exerted on one point charge due to another. The magnitude of the force is <a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=jpg::::/sites/dl/free/0073512141/663824/16_2.jpg','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (4.0K)</a>
where the Coulomb constant is <a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=jpg::::/sites/dl/free/0073512141/663824/16_3A.jpg','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (4.0K)</a>
The direction of the force on one point charge due to another is either directly toward the other charge (if the charges have opposite signs) or directly away (if the charges have the same sign).
The electric field <a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=jpg::::/sites/dl/free/0073512141/663824/symbol_E.jpg','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (1.0K)</a> is the electric force per unit charge. It is a vector quantity.
If a point charge q is located where the electric field due to all other charges is <a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=jpg::::/sites/dl/free/0073512141/663824/E.jpg','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (0.0K)</a> then the electric force on the point charge is <a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=jpg::::/sites/dl/free/0073512141/663824/16_4B.jpg','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (3.0K)</a>
The SI units of the electric field are N/C.
Electric field lines are useful for representing an electric field.
The direction of the electric field at any point is tangent to the field line passing through that point and in the direction indicated by the arrows on the field line.
The electric field is strong where field lines are close together and weak where they are far apart.
Field lines never cross.
Field lines start on positive charges and end on negative charges.
The number of field lines starting on a positive charge (or ending on a negative charge) is proportional to the magnitude of the charge.
The principle of superposition says that the electric field due to a collection of charges at any point is the vector sum of the electric fields caused by each charge separately.
The uniform electric field between two parallel metal plates with charges <a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=jpg::::/sites/dl/free/0073512141/663824/P_M_Q.jpg','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (1.0K)</a> and area A has magnitude <a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=jpg::::/sites/dl/free/0073512141/663824/16_6.jpg','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (3.0K)</a>
The direction of the field is perpendicular to the plates and away from the positively charged plate.
