Recall that a bar-shape permanent magnet behaves like a
magnetic dipole.
If we place a bar magnet in the presence of a uniform
magnetic field as shown below. What would the bar magnet
do if the bar magnet is held in place at its center, but it is free
to
PHYS 102
First Day Info
Welcome
Before starting with the material, there are
some organizational things we have to discuss
These slides will be posted in owlspace, you
dont need to write this down.
Syllabus
It is important that you read the syllabus
T
What is the goal of learning
electrostatics?
What is the goal of learning
electrostatics?
The goal is to be able to predict the force on an electric
charge if we place it in a region of space.
If we can systematically design what force is apply to
an elec
Faradays law of induction states that
Nature will always generate an to oppose changes in the
magnetic flux through the area enclosed by a conducting
loop.
Which can be written mathematically as
What exactly is this ?
In a DC circuit, the is the electric
For an arbitrary shaped enclosure with a light source inside,
if we add up all the intensity at every points on the surface of the
enclosure and multiple that by the total surface area of the enclosure,
then we will get the total power output of the light
From
applying Faradays and Ampere-Maxwells Laws to a time varying
electric and magnetic field, we got
and
We can combine these two equations to get,
and
These two equations describe the propagation of electromagnetic waves
and
The solution of these two e
Lets consider a conductor of length that moves with
velocity, through a uniform magnetic field, .
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
into the page
What will the charges inside the conductor do as the
conductor moves through the magnetic field?
What will
Faradays law of induction states that
Nature will always generate an to oppose changes in the
magnetic flux through the area enclosed by a conducting
loop.
Which can be written mathematically as
Lets consider a complementary situation to the one we examin
Amperes Law is
Here,
is the sum of the magnetic field component that is parallel to a closed
curve.
is the net current enclosed be the closed curve.
For an infinitely long, thin, straight wire carrying a
constant current we found that using Biot-Savarts
Electric field on a charged ring central axis
Take a thin ring (no thickness) of radius R with uniformly
distributed charge +Q. Find the electric field at point P that
is a distance d along the central axis of the ring.
P
d
Electric field on a charged rin
For points very close to a disk,
Here,
k is the electrostatic constant, and is a constant for a given
disk.
P
d
The result
tells us that for points close to a disk, the electric field is a
constant independent of distance.
This result is valid as long as
Electric field outside a spherical ball example
Suppose you have a spherical ball of charge, Q, (Not a point
charge). What is outside this ball?
Electric field outside a spherical ball example
We can use Gauss Law to find outside this ball of charge by
im
The equal sign in the equation does not imply causation but
correlation.
A changing magnetic flux DOES NOT cause a circulating
electric field to appear.
The equation tells us that a changing magnetic flux is
always ACCOMPANIED by a circulating electric f
We will start our discussion of Electric Potential by
refreshing our memory about gravitational potential energy
near the surface of the Earth.
We will start our discussion of Electric Potential by
refreshing our memory about gravitational potential energ
We define an Electric Potential as
We define an Electric Potential as
So,
We define an Electric Potential as
So,
Since
then,
An electric potential exist at all position in space, regardless
if there is a charged object at any given position.
The only exa
The needle in a compass is a small, light weight magnet.
On Earth, all compass needles that are free to rotate on a
horizontal plane and are far from other magnets will line up
along the same direction.
When a compass needle settles on its preferred direc
Magnetic
field of a current loop example (off central axis)
Consider a thin circular wire loop of radius located in the
plane, and carrying a steady current , flowing counterclockwise as viewed from the positive z-axis. Calculate
the magnetic field at po
For a moving charge interacting with a uniform magnetic, where the velocity of the
charge particle is NOT parallel or antiparallel to the direction of the magnetic field.
Here is the radius of the circle in which the charge will move, and is the speed of
Suppose we have a current going up the wire, lets find the force the
uniform magnetic field exerts on a straight segment of the wire that is
inside the uniform magnetic field.
The total
magnetic force the magnetic
field exerts on the segment of wire is
He
Amperes Law is
Here,
is the sum of the magnetic field component that is parallel to a closed
curve.
is the net current enclosed be the closed curve.
The Amperes law is only worth using under three circumstances:
1. When at every points on the closed curv
Consider the RLC circuit below. When the switch is at
position a, the capacitor is being charged, and when the
switch is in position b, the circuit is a RLC series circuit. If
the switch has been in position a for a long time, then at ,
the switch change
For
an inductor
and
so,
Also,
For
a Capacitor
and
so,
Also,
When an inductor is first connected to a DC power supply,
the back across the inductor is at its maximum value, and
the current through the inductor is zero, so the magnetic
field in the inducto
For
this circuit
, the current through the circuit is given by
,and the electric potential difference across the inductor is
given by
Here, is the electrical potential difference that was used to energize
the inductor, and .
So, the inductor acts like a
Quiz problem 4.
Two similar conducting sphere are separated by a distance d. One
sphere carries charge +Q and the other carries Q. They each feel an
attractive force F. If one third of the charge on the negative sphere is
transferred to the positive spher
Using Coulomb force law example
Three charged particles with q1 = -50 nC, q2 = +50 nC, and
q3 = +30 nC are placed on the corners of a 5 cm x 10 cm
rectangle as shown below.
q3 = +30 nC
10 cm
q2 = +50 nC
q1 = -50 nC
5 cm
What is the net force on charge q3
Applying the matrix method to find the currents in the
circuit,
We found
=0.091 A
= 0.0455 A
= 0.0303 A
= 0.01515 A
=+= 0.0455 A
We could have also solved this problem by first simplifying the circuit,
and thinking through how the current will move throug
When the power source for a circuit is oscillatory, meaning
the voltage changes periodically with time, we call these
circuits, AC circuits.
In a circuit diagram, an AC power source is denoted by
The simplest AC circuits is one where we have an AC power
s
3/18/2016
Phys 104 Week 9
Magnetic Fields
CRT Monitors
(Whats a CRT?!)
electron
Positron
Bubble Chambers
Iron Filings on
Bar Magnet
(Antimatter! Run!)
The Aurora
Ooooooh!
Synchrotron
(The Big Ring)
Photos shamelessly taken from online.
Drawings from Halli
1/22/2016
Phys 104 Week 2
Charge, Coulombs Law, & E-fields
Benjamin Franklin
(1706-1790)
Charles-Augustin de Coulomb
(1736-1806)
Amber
=
Discussion Question
Two uniformly-charged plastic rods are bent into quarter arcs of a circle
(radius ) and are arrang
4/9/2016
Biot-Savart
(/bio svr/)
=
Phys 104 Week 10
Amperes Law
(line integrals. OH NO!)
Sources of B Fields
4
=
Right Hand Rule
(for Ampres Law)
Junkyard Magnet
Right Hand Rule
(for Biot-Savart)
Straight Wire B Field
(Iron Filings on Field Lines)
Sole