CH 19-3

Review -- Gravitational Potential Energy and Gravitational Potential Earth If a ball is released from rest, it will move in the direction of the gravitational force on it If a charged particle is released from rest, it will move in the direction of the electric force on it.

Electric Potential Electric potential is a scalar. It is analagous to “altitude” for gravitation. A proton released from rest will move from high potential to low potential. An electron released from rest will move from low potential to high potential. Electric field always points from high potential to low potential.

Example -- Capacitor 

Poll + A B Which point is at a higher electric potential? 1.A 2.B 3.Both A and B have the same electric potential

Poll  A B Which point is at a higher electric potential? 1.A 2.B 3.Both A and B have the same electric potential

Uniform Electric Field The potential difference between two points along a path that is parallel to a uniform electric field is i f This equation can also be used if points are close together.

Example -- Capacitor 

Poll  V=0 V=9 V A What is the potential half- way between the plates? 1.9 V 2.0 V V V 5.None of the above.

Electric Potential Energy When a charged particle moves from point i to point f, the system’s change in electric potential energy is i f

Example -- Accelerating charged particle in a uniform electric field  Suppose that there are slits in the capacitor plates. An electron is released from rest at the negatively charged plate. If the potential difference across the plates is 10,000 V, how fast is the electron moving when it reaches the other plate?

Poll                          qq v What is the path of the electron?

Charged surface   1 2 The electric field near a charged surface is shown in red. A negative charge carrier released from rest at point 1 will _______________.  3 A. travel past point 2, gaining PE as it goes B. travel past point 2, losing PE as it goes C. travel past point 3, gaining PE as it goes D. travel past point 3, losing PE as it goes

The electric field near a charged surface is shown in red. A positive charge carrier is given an initial velocity v 0 to the right at point 1. Which of the following states all the possibilities? Charged surface   1 2  3 A. The charge carrier can reach point 2 and gain PE. B. The charge carrier can reach point 2 and lose PE. C. The charge carrier can reach point 3 and gain PE. D. The charge carrier can reach point 3 and lose PE. E. Two of the above are possible.

An electron going from point 1 to point 2 ______________________   2 1 A. moves toward increasing potential and gains PE. B. moves toward increasing potential but loses PE. C. moves toward decreasing potential and gains PE. D. moves toward decreasing potential but loses PE

Application - Gel Electrophoresis