1. Electric Field
Physics
Mrs. Coyle

2. Analogy The electric field is the space around an electrical charge
just like
a gravitational field is the space around a mass.

3. Electric Field
Space around a charge.

4. What is the difference?

5. Van de Graaff Generator
Builds up static electric charges.

6. Electric Field Vector, E
E = F/ qo
qo , positive test charge
E is a vector quantity
Unit: N/C
E is analogous to the gravitational field, g, where g=F/m

7. Example 1
A charge of 3µC is used to test the electric field of a central charge of 6C that causes a force of 800N. What is the magnitude of the electric field?
Answer: 2.7 x108 N/C

8. Electric Field

9. Electric Field Lines

10. Electric Field Lines of two Positive Charges

11. Electric Field Lines
Lines that indicate the strength and direction of the electric field.
The more dense the lines, the stronger the field.
Electric field vectors are tangent to the curve.
Simulation

12. Conductors and Electric Fields (under electrostatic conditions)
“The electric field is zero inside a charged conductor”.
“Excess charge on an isolated conductor resides on the surface”.
“Excess charge accumulates on sharp points”.
Electric field lines meet the conductor perpendicular to the surface of the conductor.

13. Shielding
The electric field is zero inside a charged conductor.

14. Where are you safe during a thunderstorm?
In a car or
Outdoors

15. Why can you not get radio reception in a tunnel or in a steel bridge?

16. Which field is stronger?
A B

17. Electric Field for a Point Charge
Using E=F/qo and Coulomb’s Law prove:
E = k Q
______ r2
where Q is the central charge.

18. Example 2
A test charge of +3µC is located 5m to the east of a -4µC charge.
A) Find the electric force felt by the test charge.
B) Find the electric field at that location.
Answer: 4.32x10-3 N, 1.44 x 103 N/C along the –x axis.

19. Example 3
If a test charge is moved to a location three times as far as its original location, how does the electric field change?

20. Example 4
Calculate the electric field felt by a test charge located half way between a charge of +1C and a charge of -3C, that are 2m apart.
Answer: 1.8 x N/C