# chapter 17 electric field Flashcards

what is an electric field

a region in which a charged particle experiences a force

in a uniform field what is the equation linking electric field strength, potential difference and separation of charges

E = V / D E = electric field strength, V = potential difference, D = separation of charges

in a uniform field what is the equation linking electric field strength, electric force and charge

E = F / Q E = electric field strength, F = electric force, q = charge

what is the angle between equipotentials and field lines

Equipotentials are always perpendicular to the field lines.

what is the equation for electric field strength where the field lines curve, and what is the minus for

E = -dV / dr where r is the distance along the field line

the minus shows the direction of the electric field is in the opposite direction to the increase in V

what is Coulomb’s law used for

to calculate the electric force on a charge, as well as to calculate the force of repulsion or attractiveness between 2 point charges.

what are the requirements for modelling a charged object as a point charge

is the charged object is a sphere with evenly distributed charge, so it will act as if all of its charge is at its centre so that it can be modelled as a point charge

what is the inverse square law between 2 point charges

1 / r^2, the further apart the charges, the weaker the forces between them

what can be said about the forces on 2 interacting point charges

the force on one point charge is the equal and opposite of the force on the other one

if F(electric) is positive in the coulomb’s law equation, what can be said about the 2 point charge’s interactions?

if the charges on the point charge’s are the same, there will be repulsive forces and so F will be positive

if F(electric) is negative in the coulomb’s law equation, what can be said about the 2 point charge’s interactions?

if the charges on the point charge’s are opposing each other, there will be attractive forces between them and so F will be negative

define electric field strength

force per unit charge

what is coulomb’s law

the force between 2 charges q and Q is directly proportional to each of the charges, and inversely proportional to the square of the r, the distance between the centres of the 2 spheres

when is the coulomb’s equation negative and when is it positive

negative for attractive forces, positive for repulsive forces

what is the value of electric potential V for a charge sphere where there’s a radial distance of infinity

as r goes to infinity, electric potential goes to 0

define electric potential energy

the work done to move a charge q from infinity to a distance r away from a point charge Q

how does a point charge q gain potential energy in an attractive field

the charge q gains energy as r increases, because you need to do work overcome the attractive forces between the 2 attracted point charges so that you can move them further away

how does a point charge q gain potential energy in an repulsive field

the charge q gains energy as r decreases because you have to do work against the repulsion to bring q closer to Q