When a charged body is kept at some place, a region surrounding this body comes under stress and strain. According to Coulomb’s Law, if a charge (positive or negative) is brought into this stressed region, a force of repulsion or attraction is experienced by it. This stressed region around a charged body is called electric field. Thus, a region or space around a charged body in which a charge experiences a force of attraction or repulsion is called an electric field or electrostatic field.

1. Electric Field
Physics
Mr. Berman

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
http://higheredbcs.wiley.com/legacy/colleg
e/halliday/0471320005/simulations6e/inde
x.htm?newwindow=true

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
http://online.cctt.org/physicslab/content/applets/
pointcharges/elefi_z.htm

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?
A) In a car or
B) 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 1010 N/C