Electric Fields Flashcards
What is Coulomb’s Law ?
the force between two points charges is proportional to the product of their charges and inversely proportional to the square of their distance apart.
F = 1/4πEo x Qq/r^2
(1/4πEo = 8.89x10^9)
What are electric fields ?
a force field which ca be ATTRACTIVE or REPULSIVE as its all down to charge
- the charge can be positive or negative
What is Eo ?
the permittivity of free space - 8.85x10^-12 /Fm^-1
When using Coulomb’s Law how do you treat air ?
treat it as a vacuum
- as electric field depends in the material it passes through + how easy it passes
What is electric field strength ?
is the force per unit positive charge in an electric field
E = F/Q
- is a vector
- measured in NC^-1 or Vm^-1
How do you treat a charged sphere ?
treat it as if all of its charge is concentrated at the centre of the sphere
- so charge only on surface of sphere
How do you represent electric field as RADIAL field lines ? And how to measure ?
RADIAL
- the field lines are going in if the sphere is negative
(attraction)
- the field lines are going out if the sphere is positive
(repulsion)
E = 1/4πEo X Q/r^2
How do you represent electric field as UNIFORM field lines ? And how to measure ?
UNIFORM
- produced by connecting two parallel plates to the opposite poles of a battery
- field lines move from positive (have p.d) to negative end
E = V/d
What does the graph of electric field/distance look like ?
∝1/r^2
- zero inside the sphere
- decreasing with distance from radius
- can be positive or negative graph
- area under graph = ΔV
What path does a charged particle follow when entering a electric field at a right angle ?
a parabolic trajectory
- force of field lies act perpendicular on particle
- positive particle move with field lines
F = EQ
ma = EQ
a = EQ/m
a = V/D x Q/m
What is electric potential ?
the work done in moving a unit positive charge (+1C) from infinity to a distance r within the electric field
V = 1/4πEo x Q/r
- measured in JC^-1
Why can electric potential be positive or negative ?
because repulsion between particles (e.g. P+P) will cause positive electric potential energy and attraction between particles (e.g. P+N) will cause Negative electric potential energy
- change in potential energy =
ΔV = (1/4πEo x Qq/r2) - (1/4πEo x Qq/r2)
What does the graph of electric potential/distance look like ?
∝1/r
- constant inside the sphere
- decreasing with distance from radius
- gradient = E = ΔV/Δr (potential gradient)
How to find work done in moving a charge through an electric potential difference ?
ΔW = QΔV
(work done = charge x Δelectric potential)
- derive by E = ΔV/d = F/Q -> QΔV = Fd
Electric Equipotential ?
- perpendicular to the field lines
- no work done so same potential along Equipotential line
