Electric Field Direction Forces and Fields 7

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

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

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

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 - +

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

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

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

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

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

Free Body Diagram P

Blue Red

NET FIELD

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

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

Example 3: Two charges of +3.00 C and +5.00 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

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

Assignment: Handout Reading from textbook