"The outcome of any serious research can only be to make two questions grow where one question grew before"
Thorstein Veblen

• Electric Potential Energy

  • Reminder: The change in gravitational potential energy when a particle of mass m, is raised through a height h, is given by mgh.
  
   
  • If a charge q, is moved a distance h, along an electric field line, the change in electrical potential energy is given by,

  
  PE_elec  =  q E h

  Notice the similarity to the gravitational expression (mgh) !
   

  • The electric potential energy is also equal to the work necessary to raise the charge a height h, through the field E.
  
   

• (Electrical) Potential Difference

   
  • " A potential difference of one volt exists between two points when one Joule of work is required to move one Coulomb of charge from one point to the other"
  
   
  • Between two points A and B we may write

  
  W_AB  =  V_AB q

  where V_AB  is the potential difference between A and B

  • Using the definition of electrical potential energy we see that

  
  V_AB  =  E h

  • Units of potential difference are volts

  
  1 Volt  =  1 Joule/Coulomb (J/C)

  • Since we can write E = V/h, the electric field has units V/m. (1 V/m = 1 N/C).
  
  
• Batteries, generators and fuel cells create a potential difference across their terminals.  The potential energy stored in this manner can be converted to heat, light, sound or other forms of energy when charge "flows" from one terminal to the other via a complete circuit.

   Supplementary Problems 

In the period that Einstein was active as a professor, one of his students came to him and said: "The questions of this year's exam are the same as last years!" "True," Einstein said, "but this year all answers are different."
Albert Einstein

 

Dr. C. L. Davis
Physics Department
University of Louisville
email: c.l.davis@louisville.edu