In this lesson, you will continue your investigation of the motion of electrons due to electric forces. You will explore the notion of electric field lines, which are visualizations of electric field.

Every charged object emits an electric field that extends outward into the space that surrounds it. We call this charged object the source charge. To explore the source charge's electric force, we can bring a smaller test charge close to it and see how the test charge is effected. 

The Electrostatics Model that you've used doesn't model or show you the electric force field, but instead shows how two charges are effected by each other's electric force fields. For example, in the electrostatics model if you move a positive source charge closer to a positive test-charge, the test-charge will be repelled and move away from the source charge. You can think of the positive source charge as having a force field around it that determines how other charged particles that come close to it will behave. 

Make some guesses now: How can you visually represent the force field around the source charge in the Electrostatics Model? Run the model again and observe how the particles move in order to come up with one or more possible ways to visually represent the force field.

The model below shows one possible representation of electric lines of force. Electric fields are typically represented as lines that point in the direction that a positive test charge would accelerate if placed upon the line. 

So, if you use test-protons (that have a positive charge) the lines are directed away from positively charged source charges and toward negatively charged source charges, and if you use test-electrons (that have a negative charge) the lines are directed toward positively charged source charges and away from negatively charged source charges. 

To create electric field lines and use the model:

1) Click SETUP then GO

2) Click ADD POSITIVE + SOURCE CHARGE. Drag the positive source charge anywhere in the black box. 

3) In the CREATE drop-down menu choose test-protons.

4) Click anywhere in the black box to test protons in the space you've created. Make sure to test many protons. Observe how the test proton charges behave in the space and how the electric field lines are drawn. 

5) Repeat with different numbers and positions of positive and negative source charges. You can do this by hitting the ADD POSITIVE + SOURCE CHARGE button and the ADD NEGATIVE - SOURCE CHARGE multiple times. Also, be sure to also test your space with test electrons, by selecting test-electrons in the CREATE drop-down menu.

The image below shows an electric field with an orange negative source charge on the left and a blue positive source charge on the right, the two source charges are equal in magnitude. This is called a dipolar electric field. Now imagine that you are placing test-protons at positions along the three lines shown in the image: A (left), B (middle) & C (right).

Now create a scenario like the one shown in the image below, using the Electric Field model. First, create a dipolar field with a positive source charge and a negative source charge, and then run your model by placing test-protons along the three lines shown in the image: A (left), B (middle) & C (right). Place test-charges at various positions along the three lines. 

To create a dipolar field by using the model:

1) Click SETUP then GO

2) Click ADD POSITIVE + SOURCE CHARGE. Drag the positive source to the right side of the black box, as it is in the picture. 

2) Click ADD NEGATIVE - SOURCE CHARGE. Drag the negative source to the left side of the black box, as it is in the picture. 

3) In the CREATE drop-down menu choose test-protons.

4) Click in the black box on numerous positions along the three lines shown in the picture to test protons in the space you've created. Make sure to test many protons along these lines. Observe how the test proton charges behave in the space (based on where they started) and how the electric field lines are drawn.