1. 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.

2. Electric Field Question asked by Michael Faraday Illustrated ‘lines of force’ Electric field lines

3. 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

4. Electric Field Lines Sketch the electric field lines for the charge below. +- + - + + + -- -

5. 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…..

6. 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 Field Newton Coulomb =

7. Calculating the Electric Field Positive test charges move...with the field Negative test charges move…against the field WHY??

8. Example 1 An electric field of 2.0 x 10 4 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?

9. 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?

10. 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.

11. Calculating the Electric Field Method #2 Strength of the Electric Field based on a point charge: ◦ k = 8.99 x 10 9 ◦ q = point charge ◦ r = distance away from the point charge

12. 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?

13. 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?