CHAPTER 17. ELECTROSTATICS 17.3
DEFINITION: Electric field
A collection of electriccharges gives rise to a’field of vectors’ in thesurrounding
region of space, called an electric field. The direction of the electric field at a point is
the direction that a positive test charge would move if placed at that point.Electric field lines ESBHG
The electric field maps depend very much on thecharge or charges that the map is being made for.
We will start off with the simplest possible case. Take a single positive charge with no other charges
around it. First, we willlook at what effects it would have on a test charge at a number of points.
Electric field lines, like the magnetic field lines that were studied in Grade 10, are a way of
representing the electricfield at a point.
- Arrows on the field lines indicate the directionof the field, i.e. the direction a positive test
charge would move. - Electric field lines therefore point away from positive charges and towards negative charges.
- Field lines are drawn closer together where thefield is stronger.
Positive charge acting on a test charge ESBHH
At each point we calculate the force on a test charge, q, and represent this force by a vector.
+Q
We can see that at everypoint the positive test charge, q, would experience a force pushing it away
from the charge, Q. This is because both charges are positive and sothey repel. Also notice that at
points further away thevectors are shorter. Thatis because the force is smaller if you are further away.