GEN PHYS | Electric Field, Electric Flux, & Gauss' Law

Electric Field

• how charges exert force

• region where a charge experiences electric force

• the closer the test charge to the source, the stronger the electric field

• in N/C (newtons over coulumbs)

Source Point

location of a charge in an electric field, determines the strength of an electric field

Field Point

point where the field is determined to be, commonly denoted as P

Direction of the Electric Field

By convention, it is the direction of the electrical force on a small positive test charge placed at that point.

Positive Source Charge

It leads to an outward electric field.

Negative Source Charge

It leads to an inward electric field.

What happens if the source point is positive and the field point is positive?

The electric field points away from the source point.

What happens if the source point is positive and the field point is negative?

The electric field points towards the source point.

What happens if the source point is negative and the field point is positive?

The electric field points towards the source point.

What happens if the source point is negative and the field point is negative?

The electric field points toward from the source point.

Electric Field Representation

• Field lines point away from positive charges and toward negative charges.

• The electric field vector is tangent to the field line passing through that point.

• Field lines are close together where the field is strong, farther apart when it is weaker.

When does a test charge experience an electric field?

A test charge experiences an electric field in all cases except when:

• the source charge has no magnitude

• the distance between source charge and field point is infinitely large

Electric Flux

• the measure of the electric field passing through a given surface area

• proportional to the number of field lines penetrating some surface

• has the units Nm²/C

Gauss’ Law

the total electric flux through a closed surface is proportional to the charge enclosed by the surface

Electric Dipole

• consists of two equal and opposite charges separated by a distance

• The electric field at points far away from the dipole is proportional to the dipole moment (p = qd) and decreases with distance.