Tuesday, March 11, 2008

Today in class we talked about action at a distance.  The electrostatic force is an example of action at a distance.  Non contact forces are action at a distance forces.  Gravity is another example of action at a distance forces.  A diagram was given of an electroscope.  A charged balloon was moved toward the electroscope and it acted on the electroscope at a distance.  Action at a distance forces are also known as field forces.  An electric charge creates an electric field.  This field alters the space around it.  The magnitude of electric field strength is equal to force per unit changed.  The direction of the force exerted on a positive test charge.  The electric field is made up of a single point charge; either positive or negative, a charged conducting sphere, or two point charges; both either negative or positive, and a pair of charged parallel plates.  The point charge equals all charge concentrated at a point.  A charged conducting sphere acts as though all the charge were concentrated at the center.  A field within a charged conducting sphere is zero.  The same principle is used in the faraday cage.  A diagram of a pair of positive point charges, a pair of negative point charges, and one point charge that is negative and one that is positive.  The electromagnetic field always runs in through the negative point charge and out through the positive point charge.  A diagram of charged parallel plates was shown.  The top plate was positively charged and the bottom plate was negatively charged.  The field was moving in a downward fashion, from the positive to the negative.  The intensity of electric field varies inversely with the square of the distance from the point charge.  The greater intensity seen by greater concentration of field lines.  Two diagrams showed how more lines indicated stronger electric fields and the way the way the field lines were when objects had unequal charges.