Electric Fields

What is an electric field??? It is an area of influence around a charged object. It is an area of influence around a charged object. Positively charged objects within that field will experience an electrical force. Positively charged objects within that field will experience an electrical force Electric Field Test Charge Electric Field FF

Calculating the magnitude of an electric field The magnitude is proportional to the amount of electrical force exerted on the positively charged object. The magnitude is proportional to the amount of electrical force exerted on the positively charged object. Electric Field Strength = electric force/test charge E = F electric /q 0 SI Unit = N/C

Sample Problem Mr. Luna pulls a wool sweater over his head, which charges his body as the sweater rubs against his cotton shirt. What is the electric field strength at a location where a 1.60 x C piece of lint experiences a force of 3.2 x N as it floats near Mr. Luna? q 0 = 1.60 x C F = 3.2 x N E = F electric /q 0 = 3.2 x N / 1.60 x C E = 2.0 x N/C

Calculating the strength of an electric field The strength of an electric field depends on: The strength of an electric field depends on: 1. the charge produced by the electric field 1. the charge produced by the electric field 2. the distance between the test charge and the 2. the distance between the test charge and the electric field electric field Electric Field Strength = Coulomb constant x field charge/ (distance)² E = (Kc x q)/r² Kc = 8.99 x 10 9 N m² / C²

Sample Problem A fly accumulates 3.0 x C of positive charge as it flies through the air. What is the magnitude and direction of the electric field at a location of 2.0 cm away from the fly? E = (Kc x q)/r² q = 3.0 x C Kc = 8.99 x 10 9 N m² / C² r = 0.02 m = (8.99 x 10 9 Nm²/C²) (3.0 x C) (0.02 m)² (0.02 m)² E = 6743 N/C away from the fly

Electric Field Lines Represent the magnitude and direction of an electric field with respect to the positive test charge. Represent the magnitude and direction of an electric field with respect to the positive test charge. + - More arrows = greater magnitude

When two point charges of equal magnitude, but opposite signs interact with each other, they form an “electric dipole”. When two point charges of equal magnitude, but opposite signs interact with each other, they form an “electric dipole”. Electric Field Lines

Like charged objects that interact with each another, have their field lines moving away from one another. Like charged objects that interact with each another, have their field lines moving away from one another. Electric Field Lines

When interacting charges are of a different magnitude, only a fraction of the field lines from the greater charge will move to the lesser charge. When interacting charges are of a different magnitude, only a fraction of the field lines from the greater charge will move to the lesser charge. Electric Field Lines