Electric Fields
Electric charges create electric fields Opposite charges attract; like charges repel Electric fields created by still or moving electric charges Fields radiate out in all directions, like spokes The stronger the electric field the closer the field lines Electric Field lines never cross Field lines leave the surface at 900 Fields decrease according to inverse square law Force visualized as "lines of flux" originating at positive charge and landing on negative charge
Drawing Electric Field Lines
The field lines for a positive point charge. The field lines flow out from a positive point charge.
The field lines for a negative point charge. The lines flow in towards the negative point charge.
The field lines for two positive point charges. The field lines flow away from both charges.
The field lines for one positive point charge and one negative point charge. The field lines flow out of the positive charge and into the negative charge
The field lines for a large positively charged plate. The field lines flow away from the plate on both sides. (Note: this is a small section near the centre of a large plate. This is why the field lines are not coming from the outside rim of the plate.)
Equations Definition of an electric field E = F / q Force on a point charge in an electric field F = qE Field due to a point charge
Quick Quiz Diagram the electric field lines for the following configuration of two objects. Place arrows on your field lines.
Answer Your answer may look different (especially when the details are compared) but it should share the following general characteristics with the diagram given here: The field lines should be directed from + to - or from the edge of the page to the - or from + to the edge of the page. Each field line MUST have an arrowhead on it to indicate such directions. At the surface of either object, the field lines should be directed perpendicular to the surface. There should be more lines at the pointed parts of the objects and less lines at the flatter sections.