Electric Field & Contour Lines

Gravitational Field Lines

Lines representing the gravitational pull exerted by a mass, pointing toward the center of the mass

Electric Field Strength (E)

Defined as E=keQ / r^2​, where ke​ is Coulomb's constant, Q is the source charge, and r is the distance

Electric Force (F)

The force between 2 charges calculated as F = qE

Field Line Rules

• Begin and end at charges or at infinity.

• Closer lines indicate stronger fields.

• More lines correspond to higher charge magnitudes.

• Field lines never cross.

• Field force direction is tangent to the field lines.

How are field lines drawn for an isolated negative charge?

Field lines point radially inward toward the charge

What happens to the force between two charges as the distance between them increases?

The force decreases as the square of the distance increases

Why do electric field lines never cross?

Because the field at any point has only one direction

Contour Lines

Lines on a map connecting points of equal elevation, representing the change in height

Equipotential Contours

Analogous to contour lines, representing points of equal electric potential in an electric field

Gravitational Potential Energy (Ug)

Energy associated with an object's height and mass, calculated as Ug = mgh

Work (W)

Work required to move an object through a field, equal to the change in potential energy (W = ΔU)

How can the slope of a hill be estimated from a contour map?

By calculating rise over run, where rise is the elevation change, and run is the horizontal distance

If a ball is released at a high point on a contour map, what happens to its potential energy as it rolls downhill?

It loses potential energy as it moves to lower elevation

What does it mean when contour lines are spaced closer together?

The terrain is steeper

Electric Potential (V)

Potential energy per unit charge, V = U/q located at a certain position within an electric field

Work by an Electric Field

Positive work is required to move a charge against the field; the field does negative work when moving a charge naturally

Equipotential Points

Points where the electric potential is the same, requiring no work to move a charge between them

Electric Potential Energy (U)

Energy of a charge in a field, calculated as U = qV, where q is the charge and V is the electric potential

What is the relationship between electric potential and distance from a positive charge?

Electric potential decreases as the distance from a positive charge increases

How is work related to electric potential energy?

Work is equal to the change in electric potential energy (W = ΔU)

What is the direction of the electric field around a negative charge?

The electric field points toward the negative charge

How do you determine the electric potential energy of a test charge in a field?

Multiply the charge (qqq) by the electric potential (V) at the location: U=qV

When does an electric field do no work on a charge?

When the charge moves along an equipotential line

What happens to the work required to move a charge as the field strength decreases?

The work required decreases because the force acting on the charge is weaker

Potential Energy

energy associated with the magnitude of an object’s charge and its relative position in an electric field

Electrical Potential

the potential energy per unit of charge located at a certain position within an electrical field