7.4 - Electric Fields Flashcards
What produces an electric field?
All charged particles produce an electric field around them.
What is a point charge?
For a point outside a spherical conductor, its charge may be considered to be a point charge at its centre. The electric field lines are radial.
What is Coulomb’s law?
The electrostatic force between 2 point charges is proportional to the product of the charges and inversely proportional to the square of their separation.
What is the Coulomb equation?
Fₑ = Q1Q2/4πε₀r²
Fₑ = electrostatic force between 2 charges (N)
Q1 and Q2 = 2 point charges (C)
ε₀ = permittivity of free space
r = distance between the centre of the charges (m)
what is ε₀?
A constant which represents the capability of an electric field to permeate a vacuum.
If there is a positive and negative charge, is the electrostatic force positive or negative and how would this force be interpreted?
Negative, therefore interpreted as an attractive force (since opposite charges attract).
If the charges are the same, is the electrostatic force positive or negative and how is this force interpreted?
Positive, interpreted as a repulsive force (as same charges repulse)
What is an example of a spherical conductor?
A charged metal sphere.
Which direction do the electric field lines of a uniform conductor with a positive charge go?
Outwards
Which direction do the electric field lines of a uniform conductor with a negative charge go?
Inwards.
What is electric field strength?
The electrostatic force per unit positive charge acting on a charge at that point.
(E=F/Q)
What is a non-uniform electric field?
An electric field with varying electric field strength throughout.
In terms of electric field lines, what represents a stronger and weaker field?
Stronger - lines are closer together
Weaker - lines are further apart.
What do 2 charged parallel plates that make an electric field look like?
Uniform field lines (if charge is equal) and going from the positive to negative plate?
Why is a radial field considered a non-uniform field?
The electric field strength E is different depending on how far you are from a charged particle.
What do the electric field lines around 2 point charges of opposite charge look like?
Describe and search it up.
https://study.com/skill/learn/how-to-draw-electric-field-lines-for-two-particles-with-equal-opposite-charges-explanation.html
What is the equation for the electrostatic force on a charge?
F = EQ
E = electric field strength (N/C)
F = electrostatic force on the charge (N)
Q = charge (C)
What is a test charge?
A charge with a magnitude so small that placing it at a point has a negligible affect on the field around the point.
Is electric field strength a vector or scalar?
Vector (away = positive, towards = negative)
What is the equation that finds the magnitude of the electric field strength in a UNIFORM field between 2 charges parallel plates?
E = V/d
E = electric field strength (V/m)
V = potential difference between the plates (V)
d = separation of plates (m)
What are the units of electric field strength?
both N/C and V/m
What are 2 facts that can be derived from the ‘field strength for a uniform field’ equation?
- The greater the voltage between the plates, the stronger the field
- The greater the separation between the plates, the weaker the field.
Why can’t the equation E = V/d be used to find the electric field strength around a point charge?
Field around point charge is radial, so not uniform.
What is the voltage of an earthed plate?
0V
What is the derivation of the electric field strength between plates to find the work done?
E = F/Q = ΔV/d
Fd = ΔVQ
W = Fd
W = ΔVQ
What does the motion of a charged particle between 2 charged parallel plates compare to?
It is the same as a projectile under the influence of gravity (if negative plate is at the bottom and particle is positive)
How will a non-charged act if it projected through 2 charged parallel plates?
It will travel in a straight line through?
What does the amount of deflection (of the charged particle moving through the 2 charged parallel plates) depend on?
mass - the greater the mass, the smaller the deflection
charge - the greater the magnitude of the charge of the particle, the greater the deflection
speed - the greater the speed of the particle, the smaller the deflection
What is the equation for the electric field strength of a point charge?
radial field
E = Q/4πε₀r²
What does the equation of the electric field strength of a point charge show?
- E in a radial field is not constant
- As distance from r increases, E decreases by 1/r² (when E decreases by 4, r x2)
What is the origin of the force for electric fields?
Charge
