Phy 202 & 214
Electricity &
Magnetism
Perspective from the
instructor:
PURPOSE:
This material will introduce you to the basics of electric
phenomenon
and hopefully you will obtain enough understanding of the principles
thereof to
allow you to deal intelligently with electrical problems encountered in
personal and professional life.
Overview of E & M
Our entire tirade this semester
is based
upon the idea that an electron is a small distinct object having not
only a
fixed mass and fixed dimensions, but a fixed amount of something called
charge
as well. In fact, we will assume
that this is the only moveable object in the universe that contains
charge !
(Protons contain a positive charge
equal to and opposite the charge on an electron, but they will always
be
embedded inside nuclei of atoms.)
| Therefore, all our explanations of
electricity, mine to you and yours to me, will be in terms of the
motion of electrons, and nothing else! |
Actually,
charge is more a condition than an object. Although
Milliken measured the mass of an electron, and many
have determined its charge, efforts to actually see an electron have
resulted
in seeing a cloud with bumps in it.
The
charge on an electron is -1.6x10-19 coulombs, whatever that is, and its
mass is
9.11x10-31kg. The
charge on a proton is +1.6x10-19coulombs, and its mass is 1.67x10-27kg.
The driving force of all of our
discussions will be the electric force between charged objects, namely,
First, Static Electric force- Force
due to
stationary charges embedded in an insulator.
Second, Electric Potential caused by an object containing
charge,
(Voltage), exactly like the gravitational potential due to the force of
gravity
caused by a body containing mass.
Third, we'll look at what happens
when we allow these little
charged particles to run around loose inside a conductor.
When a bunch of them are running in the
same direction at a steady rate, we call this phenomenon Current, in
Amperes,
obviously, which actually represents coulombs per second.
Fourth, We'll look at the behavior of
these little critters when they are
driven by an electric potential of a battery to run around in a bunch
of
conducting wires all connected together (DC circuits).
Fifth, we'll
take an apparent sidestep to examine Magnetism, but soon we'll return
when we
discuss the connection between Magnetism and Electricity, and finally,
we'll
discuss what happens when electrons are driven by a spinning magnet in
an AC
generator, or
Sixth, AC circuits, which will lead to the
discussion of a
funny frustrated little critter called an inductor.
He's always frustrated because when you try to push
electrons through him, he gets mad and tries to stop you.
Then if you try to stop pushing
electrons through him, he gets just as mad and tries to drag them
through
anyway.
Seventh:
Optics 1- Geometric Optics Lenses,
mirrors, reflection and refraction.
Eighth:
Optics 2- Physical Optics Wave
properties of light: interference,
diffraction, and polarization.
Ninth:
Simple Harmonic Motion, Sound & Waves
"The Facts Mam, Just the
Facts"
(famous line from popular crime
show in
the 50's called "Dragnet")
Materials are made up of atoms
which are
made up of 3 particles, electrons, protons, and neutrons. (Yeh, Yeh, we
all
know this is false.)
The
basic element of charge is the charge on an electron .
Charge on
an electron qe, or simply -e = -1.6 x 10-19
Coulombs (C)
Mass of
an electron me = 9.11 x 10-31 kg.
Charge on
an proton qp, or simply e =
1.6 x 10-19 Coulombs (C)
Mass of
an proton, mp
= 1.67 x 10-27 kg.
Charge on
an neutron = 0
Mass of a
neutron mn = 1.67 x 10-27 kg
Force
of one point charge on another: F1 on 2 = k q1q2/r122
Protons and neutrons are
embedded in the
nucleus of atoms, while electrons go whizzing around the nucleus in
orbits, or
"shells".
Like charges repel each other
and unlike
charges attract each other.
Charge can neither be created
nor
destroyed.
Steps to finding total F .
1. Draw
frame of reference (coordinate axes).\
2. Draw
a free body diagram for the point or point charge.
3. Find
the magnitude of each F , do NOT use the signs of
charges .
4. Find
the x & y components of each (Pay attention to the
signs of these).
5. Add
the x components and then the y components to find the x
and y components of the total F or E.
6. If
necessary, use PythagorasÕ Thm to find the magnitude of
the vector.
7. Use
the inverse tangent function to find u = tan-1
(Fy/Fx) .
Steps to finding total E
.
1. Draw
frame of reference (coordinate axes).\
2. Draw
a free body diagram for the point in space.
3. Find
the magnitude of each E.
4. Find
the x & y components of each (Pay attention to the
signs of these).
5. Add
the x components and then the y components to find the x
and y components of the total E.
6. If
necessary, use PythagorasÕ Thm to find the magnitude of
the vector.
7. Use
the inverse tangent function to find u = tan-1
(Ey/Ex)
.
Procedure for finding net force
on a
charged particle
|
Force Number acting on q0 |
Force Magnitude |
Fx= Fcos u |
Fy = Fsin u |
|
F10 |
kq1q0/r102 |
(kq1q0/r102)
cosu1 |
(kq1q0/r102)
sinu1 |
|
F20 |
kq2q0/r202 |
(kq2q0/r202)
cos u2 |
(kq2q0/r202)
sin u2 |
|
F30 |
kq3q0/r302 |
(kq3q0/r302) |
(kq3q0/r302)
sin u3 |
|
etc. |
|
|
|
|
Fnet on 0 |
|
Fnet x |
Fnet y |
