Electric Force

Unit Prefix Reminders Prefix Symbol Meaning Order of Magnitude giga- G 1,000,000,000 10⁹ mega- M 1,000,000 10⁶ kilo - k 1,000 10³ Base Base unit 1 10º centi- c 0.01 10ˉ² milli- m 0.001 10ˉ³ micro- μ 0.000001 10ˉ⁶ nano- n 0.000000001 10ˉ⁹

Electric Force The attraction or repulsive interaction between any two charged objects is an electric force.

Electric Force We measure charge using the unit Coulomb (C) Coulomb’s law express the force of two charges on each other. 𝐹=𝑘 𝑞 1 𝑞 2 𝑑 2

Electric Force 𝐹=𝑘 𝑞 1 𝑞 2 𝑑 2 F = Force of the two charges on each other k = 9.0 x 10⁹ Nm²/C² (Known as Coulomb’s constant) Q₁ or q₁ is charge one measured in Coulombs (C) Q₂ or q₂ is charge two measured in Coulombs (C) d = the distance between the two charges.

Electric Force Charged Particles: Electrons are negatively charged particles. 1 electron: e‾ = -1.6 x 10‾¹⁹ C 6.242 x 10¹⁸ e‾ = - 1 C Protons are positively charged particles. 1 proton: p = 1.6 x 10‾¹⁹ C 6.242 x 10¹⁸ p = 1 C

Electric Force If an object is negatively charged it most have only electrons or more electrons than protons. You can find how many electrons or how many more electrons an object has by divide the charge by the charge of an electron. 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑒 − = 𝑞 −1.6 𝑥 10 −19 C

Electric Force If an object is positively charged it most have only protons or more protons than electrons. You can find how many protons or how many more protons an object has by divide the charge by the charge of a proton. 𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝 + = 𝑞 1.6 𝑥 10 −19 C

Electric Force Practice Problems: Find the number of protons or electrons for objects A, B, C, and D.

Electric Force Practice Problems: Now find the force For objects A and B. For objects B and C. For objects C and D. For objects A and C. For objects B and D.

Electric Force Just like gravitational force if you multiply one of the charges you will multiply the force with the same quantity. Ex:2𝐹= 𝑘 2𝑞 1 𝑞 2 𝑑 2 If you multiply both charges you will multiply the force with the same quantities. Ex:(2x3)𝐹= 𝑘 2𝑞 1 3 𝑞 2 𝑑 2 = 6𝐹= 𝑘 2𝑞 1 3 𝑞 2 𝑑 2

Electric Force Practice Problems: Two charged particles interact such that they repel each other with a force of 2 N. If the charge of particle A is doubled and the charge of particle B remains the same what would be the new force? Two charged particles interact such that they attract each other with a force of -4 N. If the charge of particle A is tripled and the charge of particle B is halved what would be the new force?

Ex: 𝐹 2 2 = 𝑘 2𝑞 1 𝑞 2 (2𝑑) 2 = 𝐹 4 = 𝑘 2𝑞 1 𝑞 2 (2𝑑) 2 Electric Force Just like gravitational force if you multiply the distance between the two charged objects you will divide and square the quantify to the force. Ex: 𝐹 2 2 = 𝑘 2𝑞 1 𝑞 2 (2𝑑) 2 = 𝐹 4 = 𝑘 2𝑞 1 𝑞 2 (2𝑑) 2 Ex: 𝐹 3 2 = 𝑘 2𝑞 1 𝑞 2 (3𝑑) 2 = 𝐹 9 = 𝑘 2𝑞 1 𝑞 2 (2𝑑) 2 Ex: 𝐹 ( 1 2 ) 2 = 𝑘 2𝑞 1 𝑞 2 ( 1 2 𝑑) 2 = 𝐹 1 4 = 𝑘 2𝑞 1 𝑞 2 (2𝑑) 2 =4𝐹= 𝑘 2𝑞 1 𝑞 2 (2𝑑) 2

Electric Force Practice Problems: Two charged particles interact such that they attract each other with a force of -9 N. If the distance between the two particles is tripled what would be the new force? Two charged particles interact such that they repel each other with a force of 2 N. If the distance between the two particles is quartered what would be the new force?