1. Electric Fields

2. Electric Field Electric fields are said to exist in the area
near CHARGED objects.
A charged object in an electric field
experiences ELECTROSTATIC FORCE
The amount of force depends on:
Strength of the field (E)
Charge on the object (q)
F = Eq

3. Unit for electric field
Example #1
An object with a charge of -2 coulombs positioned in a uniform electric field experiences a force of -300 newtons. What is the strength of the electric field?
E= F/q
E = -300 N / -2 C
E = 150 N/C
Unit for electric field
strength is
Newton per Coulomb

4. Unit for electric field
Example #2
If the force is now reduced to -100N, what is the strength of the field the -2C charge is in?
E= F/q
E = -100 N / -2 C
E = 50 N/C
Unit for electric field
strength is
Newton per Coulomb

5. Example #3 F = Eq F = (3000 N/C)(0.5 C) F = 1500 N
What is the force experienced by a 0.5 coulomb charge when it is placed in an electric field with a strength of 3,000 newtons per coulomb?
F = Eq
F = (3000 N/C)(0.5 C)
F = 1500 N

6. Example #4 F = Eq F = (25 N/C)(0.5 C) F = 12.5 N
The 0.5C charge is now placed in an electric field with strength 25 N/c, what is the force the charge will experience?
F = Eq
F = (25 N/C)(0.5 C)
F = 12.5 N

7. Electric Field Maps Electric field lines can be mapped using a
POSITIVE test charge
Place the test charge near the object
2. Decide which direction the charge will move
3. Draw a field vector in the direction of motion

8. + - Field lines point: OUTWARD from + INWARD toward - Area around a
POSITIVE charge
Field lines point:
OUTWARD from +
INWARD toward - +
Area around a
NEGATIVE charge + - +

9. Electric Field Mapping
3 Rules of Electric Field Mapping
Field Lines Never Cross
Lines Always point away from + and towards –
The closer the field lines, the stronger the Electric Field is at that point + - +

10. Electric Field Mapping+ +

11. Electric Field Mapping

12. Parallel Plates

13. No electric field inside!!
Charged Spheres
No electric field inside!!

14. No electric field inside!!
Charged Spheres
No electric field inside!!
Electric Shielding!!

15. Electric Shielding
Use the idea of a charged sphere having no electric field inside and apply to electronics and other areas