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Day 4 Coulomb’s Law LO: Define and Calculate electrostatic force Do Now: AGENDA Do Now Notes Worksheet HW01 Due Mond Lightning strikes the ground and 5 µC of charge are transferred to/from the ground. How many electrons were transferred? Do Now Pick up worksheet Get out Reference Tables Get out Calculators Do Now Questions Coulomb’s Law Material from Kinetics Books Charles Augustin de Coulomb • Born: 14 June 1736 • Died: 23 Aug 1806 • 1780s He Develops theory on force of attraction/repulsion between charged particles. Coulombs Law F k Q1 Q2 r 2 . Coulomb’s Law F k • • • • Q1 Q2 r 2 . F is the force of attraction/repulsion in Newtons Q1 and Q2 are the charges in Coulombs k is the constant of proportionality in 9e9 Nm2/C2 r is the distance between the charges in “meters” Coulomb’s Law F k Q1 Q2 r 2 . • Like Newton’s Universal Law of Gravity • This is an Inverse Square Law Sample Problem • What is the magnitude and direction of the force the right charge exerts on the left charge? Sample Problem • Q1 = 5E-6 C Q2 = 1E-6 C r = 0.05 m • K = 9E9 Nm2/C2 F k Q1 Q2 r 2 . Answer Law of Superposition • Forces caused by multiple charges can be added as vectors. • What is the NET Force on the middle charge? Solution • • • • • Q1=6e C Q2 = 3e C and Q3 = -5e C e = 1.6 x 10-19C k = 8.99 x 109 N.m2/C2 r2,1 = 6 m and r2,3 = 3 m Strategy – Find F2, 1 and F2, 3 – Then Determine Net force = F = F2,1 + F2,3 Applications of Electrostatics • Attraction/Repulsion of Subatomic particles • Inkjet and Laser printers • Spray painting cars • Electrostatic Air Filters for home and industry • Capacitors – electronic equipment