Electric Fields Flashcards
Define electric field strength of an electric field at a point in space
Force experienced per unit positive charge at that point
E = F/Q (NC^-1)
Is Electric Field strength a vector
Yes, always points to direction in which a positive charge would move when placed at that point
Point away from positive charges and towards negative charges
Ideas for electric field patterns
Arrow on an electric field line shows the direction of the field
Electric field lines are always at right angles to the surface of a conductor
Equally spaced, parallel electric field lines represent a uniform field
Closer electric field lines represent greater electric field strength
Describe electric field patterns for a point charge and a sphere
Radial, decreases with distance from the centre
What is Coulomb’s Law
Any two point charges exert an electrostatic force on each other that is directly proportional to the product of their charges and inversely proportional to the square of the distance between them
Coulombs Law Equation
F = Qq/4pi epsilon0 r^2
Electrical field strength in a radial field
Decreases as you move further away from the centre of the sphere
Electrical Field strength of a radial field
E = F/q
= Q / 4pi x epsiolon0 x r^2
Graph of E against 1/r^2 for a radial field
Straight line through the origin
Key difference between a gravitational and an electric field
Masses always produce an attractive field
Charges can create both attractive and repulsive fields
Electric field strength between two parallel plates
E = V / d
V m^-1
Equation for capacitance
C = epsilon x A / d
Epsilon = Epsilon1 x Epsilon0
where epsilon 1 is the relative permittivity
Ideas used to determine the motion of the electron between plates
E = V/d
F = Eq
W = Vq
Electrons in between parallel plates
Will travel towards the positive plate, opposing direction of the electric field
Experiences a constant electrostatic force due to the uniform electric field between plates, so it has a constant acceleration
Electrons travelling from positive to negative will experience a deceleration.
Charged particles moving at right angles to an electric field
Horizontal motion:
No acceleration so horizontal velocity remains constant
Vertical motion:
a = F/m = Eq/m
initial vertical velocity = u
final vertical velocity = u + at
Leads to parabolic motion
How may a uniformly charged sphere be treated as
A point charge
Force distance graph for a point and spherical charges
Area under a force-distance graph is equal to work done
What is total work done under a force distance graph
Total area under the graph is equal to the total work done to bring the particles from infinity to a separation r
Electric Potential Energy equation
Work done = E = Qq/ 4pi x episolon0 x r
Magnitude of E represents external energy required to completely separate the charged particles to infinity
What is total work done equal to
EPE
Define Electric Potential
Work done per unit charge in bringing a positive charge from infinity to that point
Electric Potential Equation
V = Q / 4pi x epsilon0 x r
Electric Potential difference definition
Work done per unit charge between two points around the particle of charge Q
What is the capacitance of charged sphere
Ratio of the charge it stores to its potential at its surface
C=Q/V = 4pi x epsilon0 x R x v / V = 4pi x epsilon0 x R
