1. Charged Particles in Uniform Electric Fields
Forces and Fields 9

2. Consider the following:
15.0 cm +
+ + -
A positive charge of 3.0 uC is at rest at the positive plate. The charge accelerates toward the negative plate. Determine the speed of the positive charge just as it strikes the negative plate.

3. 1. Kinematics Solution

4. 2. Conservation of Energy Solution

5. The electric field between oppositely charged plates is uniform, except at the ends.+
+ + -
If a charge is placed between the oppositely charged plates, it will experience a constant force because the field is uniform.

6. eg)A charge is projected horizontally into a uniform electric field as illustrated below.+
+ + -
v = 20.0 m/s +
10.0 cm
q =+8.00 uC
m = 50.0 mg
The charge enters the electric field midway between the 2 plates. Determine the horizontal distance the charge will travel before striking the negative plate.

7. Solution:
We need several pieces of info for this solution (Work out each part)
Electric force
Acceleration of particle
3. The vertical distance it travels
4. The horizontal distance it travels

8. Example 2:
A TV with a cathode ray tube (pre flat screen TV) accelerates electrons through a potential of 25 kV using oppositely charged parallel plates, 1.5 cm apart.
Find the electric field strength between the plates?
Find the maximum speed of the achieved by the electrons.

9. Field

10. Speed
v = x 107 = 9.37 x 107 m/s

11. Electron Volt Definition: a unit of particle energy
If one electron is placed within an electric field, the electron being negative will accelerate in the opposite direction of the electric field
- Further from q1, electric field decreases
- As the electron accelerates, it gains Ek
+q1 a -
The energy gained by the electron is expressed in a unit called the electron volt

12. Electron Volt (eV) – the energy gained by an electron when accelerated through a potential difference of 1.00 volts.
+ + + -

13. The charge on one electron = 1e The charge on one proton = 1e
eg) Determine the energy gained in electron volts when a proton accelerates through a potential difference of 120V.
The charge on one electron = 1e
The charge on one proton = 1e

14. Quiz on Thursday
1.Coulomb’s Law
2. Electric Field Strength
3. Voltage
4. uniform electric plates
5. theory