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How does a ____________ (or a collection of ____________)

Electric. III. ____________ Fields. charge. charges. How does a ____________ (or a collection of ____________) exert a force on another _____________ from a distance ?. charge. charged object B. F e. charged object A. fields, E.

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How does a ____________ (or a collection of ____________)

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

  2. every charge 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 Fe that ________________. test charge acts on q test Fe/q, E = where q is the _______ charge 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 direction vector electrical force positive test charge units of E: E = Fe / q [ E ] = [ ]/[ ] = / Fe q C N

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  4. Ex 1: A positive charge q = 5.0 mC experiences an electrical force of 10.0 x 103 N when placed at the position shown. q Fe Determine the strength and direction of the electric field at the point shown. strength: E = = = Fe / q 10.0 x 103 N / 5.0 x 10-3 C 2.0 x 106 N/C Fe same (__________ direction as ____) direction:

  5. Ex 2: What electrical force will a proton experience when placed in the electric field at point P shown below? 3.7 x 106 N/C E = ____________ P Fe / q magnitude: = = = E Fe / 1.6 x 10-19C 3.7x106 N/C 5.9 x 10-13 N Fe E same direction: ______________ direction as _____ Ex 3: What electrical force will an electron experience when placed in the same point as the previous example? same _________________ magnitude: opposite __________________ direction:

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

  7. Note: • The arrows represent “_________________” that act • on a ______________ test charge q. • 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 + strength repulsion outward never cross 2 directions at one place inverse square in r

  8. For a point charge: Let q1 = the __________ charge qp, and q2 = the __________ charge q, Then, _________________ Law: Fe = kq1q2/r2 becomes Fe = and E = Fe/q becomes E = point test Coulomb's kqpq/r2 kqpq/r2 = kqp/r2 q E E For a point charge: qp r

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

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

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

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

  13. Ex. 8: The electric field around two charged ___________________________ oppositely charged plates positive negative 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 ___________________ out of the into the constant Equally constant gravitational surface bend a little

  14. an electron Suppose ___________________ is placed between the plates and released from rest. The strength of the electric field is __________________. 7.6 x102 N/C What direction will the electrostatic force on it be? up Compare the electrostatic force to the gravitational force. (9.8 m/s2) (9.11 x 10-31 kg) Fg = w = mg = (1.6 x 10-19 C) Fe = qE = (7.6 x102 N/C) upwards After released, it will fall _____________ . Its acceleration will ____________________ because the _________________ __________________________ in the ______________ E field. F acting on it remain constant constant remains constant

  15. horizontally Suppose an e- is fired ___________________ between the plates. Draw its trajectory. Ignore gravity. vi initial direction A B 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 _________________ . straight line zero parabola constant straight line zero

  16. Ex. 9: Two interesting facts: • 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.

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

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

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