ch33_mhrc

=Chapter 33. Electrical Fields Forever. And potential.=

33.1 Electrical Fields
Electric field-The space surrounding an electric charge or in the presence time varying magnetic field.

Electric fields are similar to gravitational fields, in that they both suck in, however electric fields also repel, something that gravitational fields do not do. Gravity affects everything, however electric fields only affect charged objects.

33.2 Electric Field Lines
An electric field around one or more charges can be represented by drawing lines to show the strength and direction of the field(see page 519 to 520). Rules for drawing field lines: 1) Field lines must begin on positive charges or at infinity and must terminate on negative charges or at infinity 2) The number of lines drawn leaving a positive charge or approaching a negative charge is proportional to the magnitude of the charge 3) No two field lines from the same field can cross each other.

33.3 Electric Shielding
Static charges on a conductor distribute themselves to be as far from each other as possible. This will cause the charges to accumulate on the outside surface of the conductor with none of the unbalanced charges in the center. This will also cause the largest accumulation of charge to happen where the radius of curvature is smallest, the more pointed a part of the object is the more of the charge will accumulate there as shown below: As a result of the charge moving to the outer surface there will be no electric field on the inside of a conductor.

33.4 Electric Potential Energy
Electric Potential Energy works in the same way as regular potential energy. Just as it takes work to lift an object against Earth’s gravity it also takes work to move an object in an electric field. The work done to move the object in the electric field will be stored in the object as electric potential energy and can be recovered by allowing the object to return to its initial position.

33.5 Electric Potential
Finding electric potential energy requires that the charge on the object to be moved be known, at times it is useful to be able to find the amount of electric potential energy an object would have without knowing in advance the object’s charge. Electric potential can be defined by the equation : electric potential =   electric potential energy charge Electric potential is measured in joules of energy per coulomb of charge, a quantity known as a volt   (V). Because of the units used to measure it electric potential is often known as  voltage.

33.6 Electric Energy Storage
Electrical energy can be stored in devices known as capacitors. A capacitor contains two plates or strips, one of which will take a positive charge and the other a negative. Placing the two plates close together with an insulator between them will cause the opposite charges to hold each other in place until some way is given for the charges to equalize, usually by connecting an electric circuit between the plates.

33.7 The Van de Graaff Generator
A Van de Graaff generator   is a device for building a very high voltage charge on a metal sphere which can then be used for various purposes(see 527). It works by causing a small static charge to be deposited on a moving belt in the base, the belt carries the charge to the top sphere where it is removed from the belt on the inside of the sphere. The charge then travels to the surface of the sphere leaving the generator ready to move more charge off of the belt. This will continue until there is enough charge on the sphere to either cause a long spark to some other object or to ionize away into the air.