6.2 Electric Fields Flashcards
Define Electric Field
A region of space in which charged particles
are subject to an electrostatic force
What shape of field do point charges
have?
Radial fields.
How can you model uniformly charged
spheres?
As a point charge at the centre of the sphere.
What do field lines show?
The path a positive test charge would take
when placed in an Electric Field.
What do field lines show?
The path a positive test charge would take
when placed in an Electric Field.
Which direction do the field lines point?
Positive to negative – the lines always point
away from a positive charge and towards a
negative charge
What effect does distance have on the
strength of the electrostatic force?
The greater the distance, the weaker the
force.
How is the strength of an Electric Field
represented in a diagram?
By how close together the field lines are – the
closer the lines, the stronger the field.
Define Electric Field Strength
Force per unit charge on a positive test
charge placed in the field
What is the formula for Electric Field
Strength?
E = F ÷ Q
What is Coulomb’s Law?
The force between any two point charges is
proportional to the product of their charges
and inversely proportional to the square of the
distance between them.
What is the formula for the force
between two point charges?
(Coulomb’s Law)
F= (Qq)/4pi(epsilon)r^2
Define permittivity
The ability of a material to transmit an Electric
Field (how easily the atoms become
polarised).
What is the formula for the Electric Field
Strength of a point charge?
E=Q/(4pi(epsilon)r^2)
What is the formula for the Electric Field
Strength of a point charge?
E=Q/(4pi(epsilon)r^2)
Name some similarities between
Gravitational and Electric Fields
● Both follow the inverse square law for the force.
● Point masses and point charges both produce a radial field.
● Newton’s law and Coulomb’s law formulae for force are very
similar:
● Field strength is defined by
force per unit charge/mass
Name some differences between
Gravitational and Electric Fields
● Gravitational fields are always attractive, Electric Fields
can be attractive or repulsive (depending on the charge).
● The constants of proportionality in Newton’s Law and
Coulomb’s Law are different:
Name some differences between
Gravitational and Electric Fields
● Gravitational fields are always attractive, Electric Fields
can be attractive or repulsive (depending on the charge).
● The constants of proportionality in Newton’s Law and
Coulomb’s Law are different:
What is the formula for the work done
when moving a charge in an Electric
Field?
Work done = Force x Distance moved
Define potential at a point in an Electric
Field
The work done per unit charge in moving a
positive test charge from infinity to that point
in the Electric Field.
What is the formula for the potential at a
point in an Electric Field?
V=E/Q
What is the formula for the potential
between two parallel plates?
E=V/d
What can the motion of charged particles
in an Electric Field be modelled as?
Projectile motion: the two components of
velocity are independent of each other.
Velocity perpendicular to the field is not
affected, velocity parallel to the field is.
How do you calculate the parallel
component of velocity for a charged
particle in a uniform Electric Field?
- First, calculate the time the particle is in the field (using time
= distance/speed, where distance = length of charged
plates and speed = velocity perpendicular to the field). - Use a = F/m and F=Eq to calculate the acceleration of the
particle while it is in the field (a = Eq / m). - Substitute these values into V = u + at where u is the initial
parallel velocity and V is the final parallel velocity
What is the formula for the potential near
a point charge?
V=Q/(4pi(epsilon)r)
What does the force-distance graph for a
point/spherical charge look like?
Force is inversely
proportional to the
square of the
distance.
What does the area under a
force-distance graph for a point/spherical
charge represent?
The work done
in moving the
charge.
What is the formula for electric potential
energy near a point charge?
E=Vq
What is the formula for electric potential
energy near a point charge?
E=Vq
What is the formula for the capacitance
of an isolated sphere?
Isolated spheres can store charge, so technically they can
be classed as capacitors.
Using C = Q ÷ V and the
formula for V (in terms of
Coulomb’s law), you can
derive the formula for
capacitance:
What is the formula for electric potential
energy near a point charge?
(Coulomb’s Law)
E=(Qq)/(4pi(epsilon)r)
