18.3 - Electric fields

What should you do if you are in a car during an electrical storm?If you are in a car during an electrical storm, what should you do? Assuming the car has a metal body, the safest place to be is inside the car! The reason the inside of a metal car is safe lies in the nature of electric fields and conductors. The shell of a metal car is a good conductor that shields the inside from external electric fields, including fields induced by lightning. Read the text aloud
Force field diagrams
The electric field is the organization of energy that carries the electric force between charges. The electric field is represented with diagrams similar to those used for the magnetic field. Electric field lines represent the force exerted on a positive test charge at all points in space.
  1. The electric force points toward negative charges.
  2. The electric force points away from positive charges.
  3. Lines are closer together where the force is stronger and farther apart where the force is weaker.
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Comparing gravitational and electric fields
Two different ways to represent force field linesA field-line diagram showing gravitational forces near Earth is a set of radial lines with arrows pointing toward Earth’s center. The arrows indicate the direction of the force on a test mass. The force is stronger where the lines are close together and weaker where the lines are far apart. Another way to represent a force field is with a vector diagram. In a vector field diagram, the length of each vector is proportional to the strength of the force at that location. Read the text aloud
Earth’s gravitational field is relatively easy to draw because gravity is only attractive, so all objects are attracted toward the planet’s center. The electric field is more complex because field lines must represent both attractive and repulsive forces. For a single charge, the field lines are radial, similar to gravitational fields. Furthermore, the direction of the electric field arrows depends on the sign of the charge. The force points outward, away from a positive charge and inward toward a negative charge. Read the text aloud
Consider a vector field diagram of the electric field around a negative charge. Where are the vector arrows longest? Are they longest close to the charge or far away from the charge? Show

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