Potential Difference

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Potential Difference
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Potential

• A charged particle has potential energy due to
  its position relative to another charged object
  (Electric Potential Energy)
• The particle has potential
  energy at position
  A
• Once the particle moves to
  B all PE is changed to KE
• (-) plate has low potential, ()
  plate has
  high potential

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Definition

• Potential (V) is defined as the PE per charge
  
  V PE/ q
• Units J/C 1 J/C 1 Volt (V)
• Note that only changes in PE are measurable
  called Potential Difference
• Potential difference Voltage

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Equation

• ?PE qV
• Voltage is a measure of how much energy an
  electric charge can acquire
• Since change in energy is the ability to do work,
  it is also a measure of how much work
• W qV

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Measurement

• Voltmeter instrument used to measure V between
  2 points

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Example 1

• An electron in the picture tube of a TV is
  accelerated from rest through a potential
  difference of 5000V a) what is the change in PE
  b) what is the electrons speed c) how much
  work is done?

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Example 2

• The terminals of a 12V battery differ in
  potential by 12V. Suppose that a wire is
  connected between the and terminal and 3.0 C
  of charge travels between them. How much work is
  done?

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Example 3

• An electron loses 3.45 x 10-16J of PE as it moves
  from plate A to B in a computer monitor. What is
  the voltage between the plates and which plate
  has the highest potential?

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Units of Electric Field

• Either N/C or V/m

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Example

• Two parallel plates are charged to 50V. If the
  plates are separated by .050m, what is the
  electric field they produce?

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Small Energy Unit

• J is traditional unit of energy, but with very
  small particles this unit appears very large
• Smaller unit of energy is used for these called
  the electron volt (eV)
• Before doing a problem, always change eV to J
• 1 eV 1.6 x 10-19 J

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Example

• What potential difference is needed to give a
  particle of charge of 3µC a total of
  3.54 x 109 eV of energy?