 # Coulombs Law Coulombs Law Coulombs Law The relationship

• Slides: 16 Coulomb’s Law Coulomb’s Law Coulomb’s Law The relationship among electrical forces, charges, and distance. It is like Newton’s law of gravity. But, unlike gravity, electric forces can be attractive or repulsive. Discovered by French Scientist, Charles Coulomb in the 18 th Century. Coulomb’s Law • F = K q A q. B 2 d F = Force (N) Kc = (Coulomb Constant) 9. 0 X 109 N·m 2/C 2 q = charge (C for Coulomb) d = distance (m) Important Information… • The unit of measure for electrical charge is a Coulomb (C) • Charge of 1 proton is +1. 6 x 10 -19 C • Charge of 1 electron is -1. 6 x 10 -19 C Remember… • The charge (q) of a particle is NOT a vector quantity. • Therefore, when described as “POSITIVE” or “NEGATIVE” that tells whether it is a proton or electron, but is NOT part of the magnitude of the charge. • DO NOT PUT THE NEGATIVES IN THE FORMULA. Sample Problem #1 • Two charges are separated by 0. 030 m. Object A has a charge of +6. 0 C while object B has a charge of +3. 0 C. What is the force on object A? Sample Problem #1 ANSWER F = 1. 8 x 1014 N Sample Problem #2 • A negative charge of -6 6 x 10 C exerts an attractive force of 65 N on a second charge 0. 050 m away. What is nd the magnitude of the 2 charge? - Sample Problem #2 ANSWER qb = +3. 009 x 10 -6 C Now its your turn • A negative charge of - 2. 0 C and a positive charge of 3. 0 C are separated by 80 m. What is the force between the two charges? Your turn again… • A negative charge of - 0. 0005 C exerts an attractive force of 9. 0 N on a second charge that is 10 m away. What is the magnitude of the second charge? Electric Fields • Electric Field – a vector quantity that relates the force exerted on a charge to the size of the charge • E=F/q or E=kc(q/d 2) • The magnitude of the electric field is measured in N/C (Newtons/Coulomb) Electric Field Lines • Direction of arrows indicate the charge of the field • Arrows go from positive end to negative end. • Strength of the field is denoted by the spacing between the lines (close = strong) Electric Field Lines Example • Your hair acquired an equal amount of positive charge when you rubbed the balloon on your head. What is the strength of the electric field created by your head at the location of your feet, 1. 5 meters below if the charge is 2 e 9 C?