Transcript 21-1 Creating and Measuring Electric Fields

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
 F = 0.60 N at 10o
E = ??? 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
together  strong
 Far apart  weak
 Closer

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*