unit_6_electric_fields.pdf - V Electric Fields Electric...

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V. Electric Fields Electric charge, magnetism and gravity are all forces that effect things from a distance. The “sphere of influence” of these forces is called a force field. In universal gravitation the strength of a gravitational field around a planet was called “g.” This is an acceleration in m/sec 2 , but it can also be described as Newtons of force/kg of mass (F/m=g). The gravitational field strength around earth at sea level is 9.8 Newtons/kg. On the moon it is 1.6 Newtons/kg. Similarly, in Coulom b’s law the strength of an electric field (“E”) is described by Newtons of force/Coulomb of charge. The “ Coul omb of charge” is a tiny, positive test charge. This is because charges, just like masses in gravity, exert forces on each other. To describe field strength one of the charges needs to be insignificant compared to the other, the same way one kg of mass is insignificant compared to the mass of the earth. In electric field problems the tiny charge is labeled q 1 or sometimes q 0 Rearranging the formula: E=F/q 1 =kq 2 d 2 This formula then tells you the strength of the electric field around charge q 2 . Sometimes q 2 is given the variable “Q” Electric field strength is a vector quantity. By convention, electric fields are defined using a positive test charge, so positive electric field lines point away from the originating charge (b/c like charges repel) and negative field lines point toward the charge. The closer the field lines are together the greater the strength of the field. Where field lines are parallel, field strength is uniform.
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  • Winter '17
  • Charge, Electric charge, V. Electric Fields

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