electric field generated by electric charges, the electric field is a force field filling space...

Electric Field

• Generated by electric charges, the electric field is a force field filling space around every electric charge.

• Electric Field -

How do you explain/describe something invisible?

• Charges generate and react to this field.

Electric Field

• Question asked by Michael Faraday

• Illustrated ‘lines of force’

• Electric field lines

Electric Field Lines Rules

Electric Field Lines…

1) Flow away from positive charges….

2) ….and towards negative charges

3) They move in ALL directions

4) Density of lines =strength of the field

5) Lines don’t stop, don’t intersect

Electric Field Lines• Sketch the electric field lines for the

charge below.

+ -

+ -

+++

- -

-

Electric Field• How do you know how strong

the field is?

• How could you figure out how fast and which way the water is flowing?

• Throw something in, see what happens to it

• Something small….

Two ways…..

Calculating the Electric Field

Method #1• We can measure the strength of the electric

field based on its affect on other charges.

• Using a small test charge

◦ E = Electric Field

◦ F = Force experienced by the test charge ◦ q = test charge

◦ SI Unit for Electric FieldNewto

nCoulomb=

Calculating the Electric Field

• Positive test charges move ...with the field

• Negative test charges move …against the field

WHY??

Example 1

An electric field of 2.0 x 104 N/C is directed along the positive x-axis. A. What is the magnitude and direction of the electric force on an

electron placed in the field?B. What is the magnitude and direction of the electric force on a

proton placed in the field?

Example 2

A negative charge of - 1.5×10-7 C experiences a force of 0.030 N to the right in an electric field. What is the magnitude and direction of the electric field?

Calculating the Electric Field

• Method #2

• Large point charges generate the electric field

• The field is stronger the closer you are to the charge, and weaker as you move away

• IF you know the value of point charges, the field can be calculated based on distance.

Calculating the Electric Field

• Method #2

• Strength of the Electric Field based on a point charge:

◦ k = 8.99 x 109

◦ q = point charge

◦ r = distance away from the point charge

Example 3

A point charge (q = +9.50 x 10-8 C) is generating part of the electric field. A. Calculate the strength of the electric field 2.00 m away from this charge.B. Calculate the strength of the electric field 5.00 m away from this charge.C. How far away from this point charge must you be to experience an

electric field E = 100 N/C?

Example 4

Charges of – 6.0 x 10-9 C and +4.0 x 10-9 C are 3.0 m apart. Determine the electric field at a point midway between them.A. What is the electric field generated by the negative charge?B. What is the electric field generated by the positive charge?C. What is the net strength of the electric field at the point half-way

between the charges?