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Electric Energy and Electric Potential

Electric Energy and Electric Potential. Energy Review. When we studied energy a couple of months ago there were a few major points of interest: Work is a change in energy that one object gave to another object. Kinetic Energy is moving energy. Potential Energy is stored energy.

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Electric Energy and Electric Potential

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  1. Electric Energy and Electric Potential

  2. Energy Review • When we studied energy a couple of months ago there were a few major points of interest: • Work is a change in energy that one object gave to another object. • Kinetic Energy is moving energy. • Potential Energy is stored energy. • Kinetic energy can turn into Potential Energy and vice versa.

  3. Electric Potential Energy • Earlier in the year we looked at two different types of Potential Energy: Gravitational and Elastic/Spring. • For Gravitational Potential Energy, the work done by the gravity field on the object was equal to the negative work done by the external force causing the displacement of the object. • Example: Lifting a box in a gravity field • Work done by external force: W = mgh • Work done by gravity field: W = -mgh

  4. Electric Potential Energy • The same concept holds true for Electric Fields! • When a test charged is moved by an external force in an Electric Field, the test charges gains/loses Electric Potential Energy.

  5. Potential energy due to a field • A test charge moving through an electric field can be treated just like a ball moving through a gravity field. Positive Charge Positive Charge - + Negative Charge

  6. Potential Energy due to Charges • If two charges have the SAME sign, the Electric Potential Energy is POSITIVE since it takes POSITIVE WORK by an external force to bring them together. • If two charges have DIFFERENT signs, the Electric Potential Energy is NEGATIVE since it takes NEGATIVE WORK by an external force to bring them together. • Think of this like you would a spring. If these two charges were released from their positions, they would fly apart due to the stored potential energy. + +

  7. Another way to think of it… • Since the charge would naturally want to go down (towards the negative charge) it would require work to move it up. • If I do POSITIVE work to the charge, it would GAIN potential energy.

  8. Electric Potential • Electric Potential – A scalar characteristic of an electric field, independent of any charges that may be placed in the field. • Essentially, Electric Potential (or Potential for short) is Electric Potential Energy without the charge. Electric Potential only describes the field.

  9. Electric Potential • Units: Volts Scalar Quantity Test Charge Electric Potential Source Charge Electric Field Distance Work

  10. The Electron Volt • Electron Volt (eV) – the energy a charge-field system gains or loses when a charge of 1 electron is moved through a potential difference of 1 Volt. • 1 eV = 1.6 x 10-19 J

  11. Potential difference in a field • Potential Difference is the change in the amount of Electric Potential between two different locations. • Another name for Potential Difference is Voltage. Initial Potential Final Potential Potential Difference = Final Potential – Initial Potential Arrows ALWAYS point toward the area with a lower potential.

  12. Potential Difference • This is how a battery makes a circuit work! The battery creates a potential difference in the wires, therefore moving the electrons through the wire…

  13. Potential due to a source charge • If you don’t have a uniform field as in the previous slide, the can calculate the Potential at a specific distance from source charges using the following set up. • Unlike Electric Force and Electric Field problems, you DO include the negative sign if the charge has a negative value. (A negative V is OK) q2 r2 q1 r1

  14. Practice Problem • A charge of 3 x 10-6 C is located 0.1 m to the left of the origin and a charge of - 4.0 x 10-6 C is located 0.1 m to the right of the origin. Where is the electric potential equal to zero between them?

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