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Intro to Fields

Intro to Fields. July 11. Back to Junior Science. 2 negative charges will _________ 2 positive charges will _________ A negative and a positive will __________ In general, we say that like charges __________ and unlike charges _____________ What are the 3 ways to charge an object? Explain.

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Intro to Fields

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  1. Intro to Fields July 11

  2. Back to Junior Science 2 negative charges will _________ 2 positive charges will _________ A negative and a positive will __________ In general, we say that like charges __________ and unlike charges _____________ What are the 3 ways to charge an object? Explain. What happens to the charges when 2 objects touch?

  3. What do the fields look like? • Let’s draw some pictures on the chalkboard!

  4. Coulombs Law • The magnitude of the force exerted between any two charges depends on the magnitude of each charge and the distance between them. where • Feis the electric force (N) • q1, q2 are the charges on the objects (C) • r is the distance between centres of the objects • k is the Coulomb constant (9.0 x 109 N . m2/ C2)

  5. If q1 and q2 are both positive or both negative, the electric force is positive and the charges are repelled. • If q1 and q2 are opposite in charge, electric force is negative and the charges are attracted. • For more than two charges, only two charges can be considered at a time. Once the forces have been calculated between the charge pairs, the overall force on any one charge can be determined by calculating the vector sum of all the forces.

  6. Try it… • If the force between two charges is 5.0 x 10-4 N, what is the force when the distance between the charges has been doubled? • Three point charges, q1 = 3.6 x 10-6 C, q2 = -2.7 x 10-6 C, and q3 = 4.5 x 10-6 C, are arranged in a one-dimensional line, as shown. Find the total force on q3if q1 and q2 are fixed in place.

  7. Try it… • If the force between two charges is 5.0 x 10-4 N, what is the force when the charges have been halved? • **Draw this one out on the board – 3 point charges arranged in a triangle • Page 330 #2, 4, 6, 7 • Page 334 #8, 9

  8. Electric Fields • Not only can we calculate the force between objects, we can calculate the strength of the field around an object Where • e=electric field • K=9.0x109 • q is the charge on the object • R is the distance from the object

  9. Electric Fields • A field can be represented with a field diagram which follows these rules: • Field lines come out of sources (+ve charge) • Field lines go into sinks (-ve charge) • Field strength depends on line density • Field lines cannot cross

  10. Electric Potential • See other slides!

  11. Magnetic Fields • Magnets also create fields! Draw these on the chalkboard. • Bar Magnets

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