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Electric Fields and Potential

This article explores the concepts of electric fields and potential energy in physics, highlighting their significance in understanding electric forces and interactions. It explains Coulomb's Law, the concepts of electric field strength, and electric potential energy, including how they relate to distances between charged particles. The section on electric field lines illustrates the direction and magnitude of electric forces visually. Additionally, it briefly discusses the function of capacitors and the Van de Graaff generator in producing high voltage with minimal charge, emphasizing the difference between electrical potential and potential energy.

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Electric Fields and Potential

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  1. Electric Fields and Potential • Force Fields • gravitational field • electric field • magnetic field • Action at a distance (In contrast to force fields, mechanical forces require contact.)

  2. Electric Field • The force between two charged particles is the interaction between one charge and the electric field set up by another. • Similar to the attraction of a satellite to the gravitational field of the planet it orbits. • Where the force is greatest, the field is strongest. The magnitude of force falls off with the square of distance from the source of charge

  3. Electric Fields • Coulomb’s Law defines the amount of force on a charge in an electric field • F = k q1q2 / d2 • The strength of an electric field is defined as the force placed on a “test charge” divided by the size of the charge. • E = Fon q’ / q’

  4. + Vector Representation of Electric Forces Vectors have magnitude and direction

  5. Electric Field Lines • Vector representation of fields are complicated to draw. • Electric field lines are another model to represent the strength of a field. • Arrows go from positive to negative charge

  6. Electric Field Representation of Electric Forces • Direction of force is in line with the source charge • positive source charge: pointing away • negative source charge: pointing toward source • Magnitude related to spacing of lines • higher magnitude: closer spacing • lower magnitude: lines farther apart • inverse square law

  7. 2+ 1- More complicated electric fields http://www.cco.caltech.edu/~phys1/java/phys1/EField/EField.html

  8. Electric Potential Energy • Potential Energy is energy due to the location (stored energy). • You have electrical potential energy when: • positive and negative charges are separated. • like charges are pushed together. • This is a total amount of energy for a group of charges.

  9. Electrical Potential Energy + + + + + + d F + Work is done to move the positively charged particle towards the positively charged source. This results in electrical potential energy.

  10. Electric Potential V = Ed • Electric potential energy per charge • Often called voltage • This is different from electrical potential energy. The EPE is a total for a group, EP is per unit of charge.

  11. Electric potential is measured in volts. electric potential energy electric potential = -------------------------------- charge Joule 1 Volt = -------------------------------- Coulomb

  12. Capacitor C = q/V • Stores electrical energy • Two plates separated by an insulating space • Positive charge on one plate • Negative charge on the other plate • Potential energy is in the form of the electric field between the plates • It takes work to separate the charges

  13. Van de Graaff Generator • Large metal sphere supported by an insulating tube • Charge moved from base to sphere by rubber belt • Charge generated by electric potential • Charge transferred by metal combs

  14. Van de Graaff Generator • Sphere can be raised to high potential • high voltage, about 3,000,000 volts • However charge is small so electrical potential energy is small • electrical potential is high but electrical potential energy is low • High voltage but low charge

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