21-1 CREATING AND MEASURING ELECTRIC FIELDS

Electric Field

Vector quantity that relates the force exerted on a test charge to the size the test charge Electric charge ,q, produces an electric field

that is measureable Field Strength: Stronger the force,

stronger the field Field Directions: Away from (+), towards

(-)

Equation

E = F on q’

q’

– F = force measured in Newtons (N)

– q = charge in Coulombs (C)

– E = Field Strength in Newton/Coulombs (N/C).

Example

If a 10 C charge were placed in an electric field of strength 10 N/C, what force would it experience?

E = F/q 10 C x 10 N/C = 100 N

Example

An electric field is to be measured using a positive test charge of 4.0 x 10-5 C. This test charge experiences a force of 0.60 N acting at an angle of 10o. What is the magnitude and direction of the electric field at the location of the test charge?

Known: Unknown q = +4.0 x 10-5 C E = ??? At

10o

F = 0.60 N at 10o

E = F / q 0.60 N / 4.0 x 10-5 C E = 1.5 x 104 N/C at 10o

Electric Field Lines

Strength of field is shown by spacing of lines Closer together strong Far apart weak

As previously shown, positive outward, negative inward

Electric Fields: 2 or more charges When there are two or more, the field is

the vector sum from individual charges Lines become more curved Lines will leave a positive charge and enter

a negative charge

Electric Field Lines

Also called lines of force. Lines are vector quantity with longer

vectors from stronger fields. Lines are spaced closer together where

the field is stronger. Lines go to infinity.

With two or more opposite charges, the lines start at the (+) and go to the (-).

Van de Graff machine

Transfers large amounts of charge from one part of the machine to the top meal terminal Person touches it becomes charged

electrically and the charges repel *stands hair up*