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Aim: How can we explain Electrostatic Force?

Aim: How can we explain Electrostatic Force?. Thursday, October 8 th. Homework #5. Worksheet. Units of Charge. Coulombs (C) 1 elementary charge: (1e = 1.6 x 10 -19 C) 1 Coulomb = 6.25 x 10 18 elementary charges. Example. How many Coulombs in 5 electrons?

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Aim: How can we explain Electrostatic Force?

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  1. Aim: How can we explain Electrostatic Force? Thursday, October 8th

  2. Homework #5 • Worksheet

  3. Units of Charge • Coulombs (C) • 1 elementary charge: (1e = 1.6 x 10-19 C) • 1 Coulomb = 6.25 x 1018 elementary charges

  4. Example • How many Coulombs in 5 electrons? • How many protons make up +10 Coulombs?

  5. Coulomb’s Law • The electrical force of attraction or repulsions between 2 charged objects

  6. Regents: IB: • q1 = charge on 1st object (C) • q2 = charge on 2nd object (C) • r = distance between objects

  7. 2nd IB equation: • What’s different? • k can be written in terms of another constant, ε0, the permittivity of free space • k = 1/4πε0

  8. Graph of Coulomb’s Law Force Distance

  9. Coulomb’s Law applies to objects that are much smaller than the distance between them • Ideally used for point charges (remember point masses?)

  10. Notice anything?

  11. Both are inverse square laws  F 1/r2 • Both have a proportionality to a property of each object (mass for gravity, electric charge for electricity) • Both act over a distance • MAJOR DIFFERENCE: gravity is always attractive, electric force can be attractive or repulsive

  12. Examples • q1 = +2.0C, q2= +2.0C, r = 5m. • Find F F = 1.4 x 109 N

  13. q1 = -10.0C, q2= -10.0C, r = 2.0m. • Find F F = 2.2 x 1011 N

  14. Find F between electron and proton, separated by 1.5 x 10-10 m F = -1.0 x 10-8 N

  15. If F is positive, the force is repulsive/attractive • If F is negative, the force is repulsive/attractive

  16. Now your turn…. • A negative charge of -2.0 x10-4 C and a positive charge of 8.0 x 10-4 C separated by a distance of 0.30 m. F=? • A negative charge of -6.0x10-6 C exerts 65 N on second charge that is 0.050 m away. Second charge = ? • For extra credit…Sphere A (+2.0x10-6C) is located at the origin, Sphere B (-3.6x10-6C) is located at +0.6 m on the x-axis, and sphere C (+4.0 x10-6C) is located at +0.8 m on the x-axis. What is the net force on Sphere A?

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