Nine Chapter 3

The Motion of Charges in Electric Fields

• Consider a mass (m) with charge q in an electric field produced by charge Q a distance r₁ away.

• The electrical force is

• The force causes acceleration according to

F = ma

• Note that as the charge moves, F_e changes because r changes. Therefore, since F_e changes, so does acceleration.
• For this situation, energy considerations are easier to handle.

• This last expression tells us that any change in E_k or E_p results in a change in the other
  • i.e. E_p decreases by X J then E_k increases by X J and vice versa.
• If the electric field is uniform (unlike the above analysis), then the calculations are simplified.

e.g. Consider a charge q in a field of uniform strength E between two parallel

plates.

• For this situation, when considering energy,

• The last equation is our defining equation for electric potential difference

December 30, 2013