Distance (fundamental): 3 dimensions; requires VECTORS
Motion (combines distance and time)
Forces cause changes in motion (Newtons Laws of Motion); types of force
Work and Energy (Conservation of Energy)
Power (rate a
One way to explain this action at a distance is this: each charge sets up
a field in space, and this field then acts on any other charges that go
through the space.
One supporting piece of evidence for this idea is: if you wiggle a charge,
the force on a
In order to account for both attractive and repulsive forces and describe
electricity fully, we needed to have two different kinds of charge, which we
call positive and negative.
Gravity with only attractive forces needed only one kind of mass.
When we break matter up, we find there are just a few fundamental
particles: electron, proton and neutron. (Well consider whether these
three are really fundamental or not in the last part of this course, and
whether there are any more fundamental particl
E from1 = k q1 / r122 for a point charge, and
g = G M / r2 for a mass. Why do both have an inverse square of
distance (1/r2) ?
If we consider that the field consists of a bunch of moving particles that
make up the field, the density of particles, and henc
In the first laboratory experiment, Simulation of Electric Fields, we use a
computer to perform the many vector additions required to look at the
electric field due to several charges in several geometries.
With the calculus, we can even determine the ele
Formula Cheat Sheet
F1on2 = k q1 q2 / r122
PE12 = k q1 q2 / r12
Fon 2 = q2 Eat 2
PEof 2 = q2 Vat 2
Eat 2 = k q1 / r122
Vat 2 = k q1 / r12
S F = ma
KEi + PEi = KEf +PEf +Elost
Ex = -DV / Dx
Through how many volts will a proton h
Since the potential energy of one charge due to another charge is:
PEel = k q1 q2 / r12
and since voltage is defined to be:
Vat 2 = PEof 2 / q2
we can find a nice formula for the voltage in space due to a single charge:
Vat 2 due to 1 = k q1 / r12Since vo
Suppose that we have an electron orbiting a proton such that the radius of
the electron in its circular orbit is 1 x 10-10m (this is one of the excited states
of hydrogen). How fast will the electron be going in its orbit?
qproton = +e = 1.6 x 10-19 Coul
The unit for voltage is, from the definition:
Vat 2 = PEof 2 / q2
volt = Joule / Coulomb .
Note that voltage, like field, exists in space,
while energy, like force, is associated with a particle!
In electricity we have:
PEof 2 = q2 * Vat 2 .
In gravity (a