Electrostatics Flashcards
What is the principle of superposition, in the context of electrostatics?
The interaction between any two charges is unaffected by the presence of others. Hence electric fields can be added together.
What is the relationship between the electric field and the electric force?
The electric field is the electric force per unit charge.
Hence F = qE
What is the formula for coulomb’s constant?
What is the electric field due to a point charge?
Where r is the distance from the point charge to the point where the field is being measured (the “field point”)
By convention, the test charge is ________
Positive
What does the direction of electric field lines indicate?
The direction of the electric force on a positive test charge if one were placed at that location.
To find the electric field due to multiple point charges…
…just find the electric field due to each point charge and add them up.
What is the general expression for the electric field due to a continuous charge distribution?
Where r is the distance from the differential charge “dq” to the point where the field is being measured. In general, dq can be a function of position.
In order to find the electric field due to a line of charge…
…replace “dq” with lambda dl, and integrate from one end of the line to the other.
In order to find the electric field due to a surface charge distribution….
… replace “dq” with sigma da, and preform a double integral over the surface.
In order to find the electric field due to a volume charge distribution…
…replace “dq” with rho dTau, and perform a triple integral over the volume.
Can electric field lines cross eachother?
No, because at the point they cross there would be two directions for the electric field.
The electric field lines due to a positive point charge look like…
spokes pointing outward radially.
What does the spacing of electric field lines tell you?
The magnitude of the electric field in that region. Think about this in terms of flux, and how many electric field lines a guassian surface would capture there.
What is the general expression for the flux of the electric field through a surface?
Where “da” is the differential area vector, pointing outward, normal to the surface.
