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Understanding Electrostatic Force Concepts

Explore Coulomb's Law, units of charge, and examples of calculating electrostatic forces between charged objects. Discover the inverse square law and differences between gravity and electric force. Practice solving force calculations using Coulomb's Law.

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Understanding Electrostatic Force Concepts

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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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