1. How does a ____________ (or a collection of ____________) exert a force on another _____________ from a distance ? charge charges charge charged object A charged object B FeFe Answer: By means of their electric ________________. (Note: The letter E can also represent ______________.) fields, E III. ____________ Fields Electric energy

2. An electric field E exists around ___________________. Its strength is found by placing a positive "__________________" (any charge) q in the field and measuring the electric force F e that ________________. E = E is a _______________ because it has ______________. Its direction is given by the direction of the _____________ ____________ that acts on the __________________________ that is placed in the field units of E: E = F e / q [ E ] = [ ]/[ ] = / every charge F e /q, vector electrical force positive test charge test charge acts on q N C FeFe q direction where q is the _______ charge test

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4. Ex 1: A positive charge q = 5.0 mC experiences an electrical force of 10.0 x 10 3 N when placed at the position shown. Determine the strength and direction of the electric field at the point shown. strength : E = = FeFe q direction : (__________ direction as ____) F e / q 10.0 x 10 3 N / 5.0 x 10 -3 C 2.0 x 10 6 N/C same FeFe

5. Ex 2: What electrical force will a proton experience when placed in the electric field at point P shown below? magnitude : = = FeFe Ex 3: What electrical force will an electron experience when placed in the same point as the previous example? P E = ____________ direction : ______________ direction as _____ magnitude: _________________ direction: __________________ F e / 1.6 x 10 -19 C 5.9 x 10 -13 N same E opposite F e / q E 3.7x10 6 N/C

6. Ex 4: The E field around a ______________ point charge q p + FeFe positive pos. test q qpqp 2 force lines  stronger 1 force line  weaker

7. Note: 1.The arrows represent “_________________” that act on a ______________ test charge q. 2.E is directed _____________________ away from “____” 3. The closeness of the lines show the field ___________. The arrows show ________________ because they point ______________________. 5. Field lines _________________, because if that were true, the field would have ______________________________ 6. E is _________________________. It is NOT constant. lines of force positive radially outward + inverse square in r repulsion outward never cross 2 directions at one place strength

8. For a point charge: Let q 1 = the __________ charge q p, and q 2 = the __________ charge q, Then, _________________ Law: F e = kq 1 q 2 /r 2 becomes F e = and E = F e /q becomes E = EE qpqp r point test Coulomb's kq p q/r 2 For a point charge: q = kq p /r 2

9. Ex 5: The E field around a ____________ point charge. Note: 1.The arrows represent “__________________________.” 2. E is directed radially __________ towards the ___. 3. E is __________________________. It is NOT constant. 4.The _________________ of the lines represents the field strength. 5.The arrows show ________________because they point __________________. 6.This E resembles Earth’s _____________________ field as it would be seen _____________________ - pos. test q FeFe negative inward inverse square in r closeness attraction inward lines of force "-""-" from far away gravitational

10. Ex 6: The E field around 2 __________________ charges. Start by placing a ____ test charge q at one point. Find resultant of the forces from both charges on q. + - Then repeat for every other possible point. where F e+ = F e due to the ___charge and F e- = Fe due to the ___charge R The result will be… q F e+ F e- pos. opposite + -

11. R Note: 1. Near each charge, E is like that of a ___________ charge. 2.The direction of the force at any point is ______________ to the field lines. 3.Lines are always: ____ ________ the “+ and ___________ the “-” 4.E lines ______________ cross b/c the net force at any point ____________________________________. single tangent out of into never cannot have two directions

12. Ex. 8: The E look like around two ______________ charges will look _______________________ but with ______________________________________ the arrows pointing in. Ex. 7: For two _________________ charges, E will look like: R positive q negative the same

13. Ex. 8: The electric field around two charged ___________________________ Notes: 1. Lines are ____________ “+" and _________________ “-” 2. Within the plates, E is _______________. _______________ spaced lines  ____________ field 3. Same idea as the constant ___________________ field near Earth’s ________________. 4. In reality, the lines near the edges ___________________ positive negative oppositely charged plates out of the into the constant Equally constant gravitational surface bend a little

14. Suppose ___________________ is placed between the plates and released from rest. The strength of the electric field is __________________. What direction will the electrostatic force on it be? After released, it will fall _____________. Its acceleration will ____________________ because the _________________ __________________________ in the ______________ E field. Compare the electrostatic force to the gravitational force. F g = w = mg = F e = qE = (9.11 x 10 -31 kg) (1.6 x 10 -19 C) 7.6 x10 2 N/C an electron upwards remain constant F acting on it remains constant constant up (9.8 m/s 2 ) (7.6 x10 2 N/C)

15. In region A, it follows a ____________________ because the net force acting on it is _________________. Within the plates, it follows a ____________________ because the net force acting on it is _________________ In region B, it follows a ____________________ because the net force acting on it is _________________. Suppose an e - is fired ___________________ between the plates. Draw its trajectory. Ignore gravity. horizontally vivi straight line zero A B initial direction straight line zero parabola constant

16. Ex. 9: Two interesting facts: 1.Any charge placed on a conductor ____________________ ___________________________. 2. The E field inside any conductor is ____________. This is called ______________________________. remains on the surface of the conductor zero electrical shielding

17. Why are you safe within your car during a lightning storm? Any charge resulting from a strike remains on the outside, and the E field within the car will be zero.

19. You are a __________________. E field lines "end on" the surface of a conductor and___________________. Painting rooms with a _______________ paint prevents ( electro magnetic) radio signals from entering. cannot get in conductor conducting

22. Tesla invented: modern generators and motors (Niagara Falls) radio electromagnetic induction tesla coils x-ray tubes arc lighting etc…and died penniless…