The same theories that you have used with gravitational fields also apply to electric phenomena.  After all, if a charged balloon can make strands of hair stand on end without touching them, the balloon must be surrounding itself with an  electric field .  In this case, the balloon is the source of the field, so it is called the  source charge .  The individual strands of hair are acting as test bodies, which provide physical evidence that the balloon is surrounded by an electric field.



Electric Field:  a property of the space around a source charge that enables the source charge to exert forces on test charges in the region

 

Try This: Exploring Electric Field Lines

The Electric Field Lines simulation will help you visualize both the magnitude and direction of the electric field surrounding a single point charge. Once you open the simulation, follow the instructions below.

 

Note: In the simulation, consider the large coloured charge the source charge for the electric field.  The small blue boxes represent positive test charges influenced by the field.  

 

1. Press the "add +" button and drag the positive charge randomly around the display area.  Notice the vector arrows that extend outwards when the charge passes near all the points on the grid.  The vector arrows represent the electric field produced by the spherical charge.  Sketch the electric field vectors on diagrams like those shown below.

 

 

2. In what direction does the electric field always point for a positive source charge?

 

3. On the simulation, switch the charge to negative by dragging the positive charges to the "trash" and selecting the "add -".  Sketch the electric field vectors on diagrams like those shown below.

 

 

4. In what direction does the electric field always point for a negative source charge?