18-3-electric-field_summary

This section is about Electric Fields in physics. The learning objectives include calculating the strength of an electric field and creating and interpreting drawings of electric fields. The concept of electric fields is similar to gravitational fields, where it represents the force that surrounds any object and acts on another object at a distance without apparent physical connection. An electric field is generated by electric charge and tells us the force per unit charge at all locations in space around a charge distribution. The electric field extends into space around the charge distribution. If a test charge is placed in the field, it experiences a force in a given direction, and the force exerted is proportional to the charge of the test charge. The electric field is a vector field that points in the same direction as the force on the positive test charge. The units of electric field are N/C. The magnitude of the electric field created by a point charge Q is given by the equation E = kQ/r^2, where k is Coulomb's constant, Q is the charge, and r is the distance from the point charge. To create a three-dimensional map of the electric field, the test charge is placed in various locations in the field, and the force on the charge is measured at each location. The electric field can be visualized by drawing arrows at each point where the test charge is placed, with the length of the arrows proportional to the strength of the electric field. The electric field lines originate from positive charges and terminate on negative charges. The electric field gets stronger as we approach the charge that generates it, and the electric field lines become denser as we approach the charge. The electric field due to multiple charges may be found by adding together the electric field from each individual charge, and electric-field lines cannot cross each other. The simulation "Probing an Electric Field" allows students to place charges on a screen and observe the electric field that they form. The video "Electrostatics (part 2): Interpreting electric field" explains how to calculate the electric field of a point charge and how to interpret electric-field maps in general. The Grasp Check asks whether if a point charge has electric field lines that point into it, the charge must be positive. The answer is false. The Worked Example provides practice problems to solve.