1. Electric Field Direction
Forces and Fields 7

2. Electric Field Direction
The direction of the electric force that a positive charge and a negative charge experience within an electric field are opposite
+ q1 Fe + -
attract
Fe repel

3. The direction of the vector, E is defined as the same direction as the electrical force exerted onto a positive test charge placed within an electrical field
The direction of the electrical force on the positive test charge is used to indicate the direction of the electrical field
- q1 Fe +
q2 test charge

4. Examples
+ q1 Fe +
q2 test charge
-q2 Fe
q2 test charge +

5. Field Direction
The direction of E about a negative charge is toward its center
The direction of E about a positive charge is away from its center - +

6. Irregular Shaped Object
Electric field is
stronger at the tip as charge is more
concentrated there.

7. Hollow Conducting Object
The electric field inside a
hollow conductor is zero.

8. Field Direction Between Charges
The direction of E is from positive to negative + -

9. Comparison of Fields
Gravitational
Electrical
Force is . . .
Attractive
Attractive or repulsive
Field Direction
Direction of F on mass
Direction of F on + charge
Field direction
Toward source
Toward or away from source
Field varies

10. Net Field Example:
5.00 cm
+2.00uC
+3.00uC P
Find the net electric field at point P, midway between the two charges.

11. Free Body Diagram P

12. Blue
Red

13. NET FIELD

14. Example 2: Determine the net E at a point P midway between the two charges shown below.q1 q2
+9.00 uC
+4.00 uC
10.0 cm
E Net P E1 E2

15. midway between two identical charges, E = 0
midway along a line joining the centers of two unlike charges, the electric field E is uniform in strength
+1.0 C
-1.0 C q1 q2
midway between two identical charges, E = 0 q1 q2
+1.00 C

16. Example 3:
Two charges of C and C are 10.0 cm apart. At what distance from the 3.0 C charge will the field be zero? q2 q1
+3.00 C
+5.00 C
10.0 cm x
10 - x

17. q2 q1
+3.00 C
+5.00 C
10.0 cm x
10 - x
Solution:

18. Assignment:
Handout
Reading from textbook