What types of forces are gravitational and electric forces?
Conservative Forces
Why are gravitational and electric forces conservative forces?
They have fields that can store energy in the form of potential energy.
How do we know a conservative force exists?
A conservative force exists only if there exists some potential energy function U(r).
What is related to the work done by a conservative force?
The change in the potential energy of the system.
Formula for work with a constant force
W = F • ds (all vectors)
naag
Nature abhors a gradient
a particle released in a field moves in…
moves in the direction of decreasing potential.
Femtometer
10^-15
positron
Same characteristics as electron, but positive
∆V
Potential Difference
Potential is a property of what?
The generating charge only.
What type of quantity is ∆V?
Scalar quantity, that exists even without a test charge experiencing it.
Units of ∆V
J/C = Volts
E field lines point in which direction?
They point in the direction of decreasing potential.
Alpha particle
Helium Nucleus, particle with 2e charge (2 protons)
Equipotential Surface
A collection of points with the same electric potential.
Capacitance dependent on which type of factors?
Geometric factors only, not dependent on battery
What has to happen for a capacitor to be charged?
The first charge enters the plate easily, but afterwards, an external agent (the battery) must do positive work to force another charge on the battery. The work (energy) is stored in the electric field as potential energy. The work done is not constant, but varies with q(t)
Energy density
u
What happens to charge when the capacitor plates are separated further without a battery?
It stays the same, nowhere to go.
Battery does what to a capacitor when attached?
It maintains a constant potential.
Dielectric
Non-conducting material inserted between capacitor plates to control capacitance and the separation of plates (d)
Dielectric constant
intrinsic property of plate material, not geometry. (kappa)
What does it mean for a dielectric to break down?
It will no longer function as an insulator, to form a conducting path between the plates.
dielectric strength
The maximum electric field that a material can withstand without breakdown is called the dielectric strength [V/m].
Maximum potential difference across a ppc is…
∆Vmax = Emax * d
When will a dielectric breakdown?
∆V > ∆Vmax
Inserting a dielectric in between the plates of a capacitor does what to potential difference?
It limits the maximum potential difference that can be applied to the plates to some ∆Vmax.
