A
Ch 28 issues
(forces and
torques on
charges and
currents)
can often be
confused with
Ch 29 issues
(the making of
magnetic fields
by charges and
currents).
I
Torque on a loop of
current-carrying
wire.
= N I A x B
A
This is the
right-hand rule
associated
In Lectures 13 and 14, we had this problem.
It would be helpful at this time to go back and review
Slides 2 through 18 in Lecture 14. What comes next
will make a lot more sense if you do.
We have a non-conducting cylinder
of radius R = 1 meter, surrounded
Faradays Law
number of coils
d
_
O Eds = - N
dt
curve
BdA
surface
= V = I R
curve is the
circuit that receives
the induced current
entire integral
on the left side
is the voltage
induced in the circuit
surface of integration
is the area enclosed
by the ci
Today we look at a corollary to Faradays Law, called
Lenzs Law. Lenz is a convenient principle to find the
direction of the induced current in a circuit w/o the need
to do any extensive computation.
You will find it valuable in one of two ways. Either to
So far with Faradays Law, weve been looking at examples
where the magnetic field changed as a function of time
and/or position within the circuit loop.
Today we keep the magnetic field fixed, and look at
situations where the geometry of the circuit loop u
Heres a reminder of an exercise
that you did in Lecture 13.
Two charges. Looking for the
electric field produced
at point P.
+Q
d
R
P
d
+Q
Electric fields point away from
positive source charges.
Needed vector addition to find the
net rightward field.
+Q
Friday is Exam 3.
It covers Ch 24, 25, 26, and 27.
Practice exams are available on Cobra.
This week we have review in lab (copies of a practice exam
will be available) as well as
the lab assessment on building a resistor network.
E
In Lecture 11,
we looke
Electric force on a test charge
FE = QT E
Magnetic force on a test charge
FB = Q T v T x B
velocity of
test charge
crossproduct
(vector
product)
magnetic
field
An electron is released from rest and moves through a
potential difference of 150 V.
Find the s
Magnetic force
on a single charge.
F = Q v x B
Magnetic force
on a section of
current-carrying
wire.
F = I L x B
Torque on a loop of
current-carrying
wire.
= N I A x B
Magnetic field
made by a
single moving
charge.
B =
0QS
4r2
vS x ^r
We have a negative
We have been looking at the magnetic force on a
moving charge. Today we consider a section of wire
filled with moving charges and look to find the
collective force exerted.
I
L
The region of the wire is filled
with a magnetic field directed into
the scree
Exam 2 this Friday.
It will cover Chapters 21, 22 and 23.
Relevant material can be found in Lectures 9 through 17,
as well as the homework problem found at the end
of Lecture 18.
Two practice exams have been posted on Cobra.
I will have copies of one of t
In Lecture 11
you did this example
where you found
the electric field
at a point,
with Q = +5x10-6 C.
+Q
+Q
A
-Q
+Q
80 cm
Each charge
contributed a vector
field to the point
and we added the
fields as vectors
to find the
resultant.
+Q
+Q
-Q
+Q
80 cm
+Q
+Q
A suggestion for todays Lecture 16 is to view it
in Normal mode in PowerPoint instead of in SlideShow.
Certain features show up jumbled in SlideShow and in the
printed version, but things look fine in Normal mode.
We have a flat sheet of non-conducting
ma
Lecture 13 closed with a challenging problem.
Non-conducting cylinder with a charge density.
If you were able to get it, youre off to a great
start in your understanding of Gauss Law.
The next few slides should help with your conceptual
understanding of c
In the HW for today, you found the
electric field due to the presence of a set
of source charges.
Today we look at the electric field due to
the presence of a continuous line of charge.
This can be done using the Ch 22 stuff that
you have been doing, or i
Exam 2 is next Friday. It will cover Ch 21,22, and 23.
So we have a fair amount of time to digest all of
the Gauss Law stuff.
This Lecture 17 has two objectives. One is to go through
the planar non-conducting example posed in Lecture 16.
The other is to g
An electron with a speed of 5x106 m/s is launched as
shown into a region with an upward electric field
of 500 N/C. Find yf.
I know many of you got the answer here.
But I wanted to show some details.
yf
40o
20 cm
Everywhere the electron goes, it
finds the
F =
k Q1 Q2
2
r
^
r
we have been working with Coulombs Law
this k constant is 9x109
F =
Q1 Q2
40
2
r
^
r
But you will also see it represented like this,
using a different constant.
k =
0 =
1
40
1
4k
= 9x10
9
= 8.85x10
-12
Ive spared you the units here th
In the homework, youve been
using Coulombs Law to find the
net force on charges.
The 2D vector addition thing is
usually rusty at this point in
142, so the HW theme this
week is to brush up on x and y
components.
In doing #11, you notice that
there were 3
Today we look at a couple of examples that should
help you see how Gauss works for spherical and cylindrical
geometry. Well hold off on the planar case until
Lecture 16, so we have the chance today to settle some
issues.
There are many nuances to this Gau
Physics 2101
Section 3
May 7th: Chap. 20
Announcements:
Final Exam: May 11th
(Tuesday), 7:30 AM at HoweHoweRussell 130
Make up Final: May 15th
(Saturday) 7:30 AM at Nicholson
119
Chapter 20
20Irreversible processes
Final Exam for those who need
extende
Physics 142 Exam One
Name _
Consider all data and constants given to be exact numbers.
Show work to receive credit for your answers.
Work answers to 3 significant figures. Remember units.
TK = TC + 273o
PV=nRT
Q=mcT
Q
kA(TH-TC)
Q
=
t
L
cice = 0.53
Q
t
cal
In Lecture 5 we looked at the constantpressure and constant-volume processes.
Today we get into the constant-temperature
and adiabatic processes.
With the Q and W information from each of
these four, we can quantify the efficiency
of many physical engines
We have the first exam next Friday. Two practice exams w/answers are
posted on Cobra. I will also distribute a hardcopy of one of the practice exams
at the lab sessions Tuesday and Thursday. There will also be two lab
assessments at the beginning of the l
A heat engine is a system that
operates in a repeatable cycle
of thermodynamic processes.
The second law of
thermodynamics states that this
series of processes cannot
convert fuel into work with
100% efficiency.
These next three sessions are devoted to
un
Two practice exams are available on Cobra.
Hardcopy of one will be available at lab this week.
Two lab assessments in lab this week.
Exam Friday (here in M124).
You can start the exam 3 minutes before the hour and we
will finish 53 minutes after the hour.
Newtons Law of Gravitation
F =
G m1 m2
2
r
G = 6.67x10-11 (m3)/kg/s2
force of attraction
between masses
F =
m1
G m1 m2
2
r
r
distance
of separation
force is
inverse-square
m2
F =
m1
G m1 m2
2
r
^
r
forces equal and opposite
Newtons Third
use radial unit
Physics 142 Exam One
Name _
Consider all data and constants given to be exact numbers.
Show work to receive credit for your answers.
Work answers to 3 significant figures. Remember units.
TK = TC + 273o
PV=nRT
Q=mcT
Q
kA(TH-TC)
Q
=
t
L
cice = 0.53
Q
t
cal
In Lecture 5 we looked at the
constant-pressure and constantvolume processes.
Today we get into the constanttemperature and adiabatic processes.
With the Q and W information from
each of these four, we can quantify
the efficiency
of many physical engines.
Homework assignments are due at
each lecture session.
HW is not handed in for a grade, but
the quizzes will be related to HW
problems. Its a good idea to keep a
notebook of completed HW problems.
Next week starts the schedule
of lab experiments. I would a