Chapter 22 - Electric Fields Flashcards
Electric field strength (E):
The force experienced per unit positive charge at that point
Electric field strength formula
E = F/Q
Electric field lines
- At right angles to the surface of a conductor
- Equally spaced lines show a uniform field
- Closer lines show a stronger field
- Point from a positive to a negative charge
Coulomb’s law
F = Qq/(4πε0r^2)
Using Coulomb’s law
Substitute the minus when using negative charges, a negative value is an attractive negative field and a positive is repulsive
Electric field strength using Coulomb’s law
E = Q/(4πε0r^2)
Derive by substituting Coulomb’s law into E=F/Q
When is the force a maximum
When the separation between the centres is equal to the sum of each radius
What do field lines show
The direction of force a positive charge would experience
Parallel plates electric field
Produce a uniform force with the same direction at any point
εr
The permittivity relative to the permittivity of free space
ε
ε0 x εr
Electric field strength in terms of potential difference
E =V/d
Capacitance in a vacuum
C = ε0A/d
Capacitance general formula
C = εA/d
Resultant electric potential
Sum the electric potential of each
Moving non-parallel to an electric field
Resolve perpendicular and parallel
Perpendicular velocity is constant
Parallel component changes due to the electric field
Electric potential definition
The work done to bring a charge from infinity to a point in an electric field per unit positive charge.
Electric potential equation
V = Q/4πε0r
Electric potential energy in terms of electric potential
E = Vq
Electric potential energy
E = Qq/4πε0r
Investigating Coulomb’s law
Take a top-pan balance with a positive charge on a support and another above on a rod
Set the balance to 0 before the second charge is added and find the force using mg as the top charge is added
Field lines with a positive sphere and a negative plate
Curve from the sphere to the plate, must be perpendicular to the surface of the sphere and the plate
