Electric Currents and Circuits Summary
(K. Honscheid Physics 112)
CURRENT: Electric current is charge in
motion. The amount of current is the charge per
unit time that flows past some point. The
direction of the current is conventionally taken
as that of
Chapter 18
Conceptual Questions and
Concepts and Calculations
CONCEPTUAL QUESTIONS
ssm Solution is in the Student Solutions Manual.
1. In Figure 18.8 the grounding wire is removed rst. followed by
the rod. and the sphere is left with a positive
Advice for Physics 111 Students Prof. John Beacom, Wi09 No warranty about the correctness, specific utility, or overall worthiness of this advice is given. At the time of writing, it could not be directly verified that this advice is actually endorsed by
Summary Lecture 17
Wavefronts and
Snells Law of Refraction
Smaller velocity
Wavefronts closer together
Change in direction
Refraction
Normal
1
Medium 1 (n1)
2
Medium 2 (n2)
Caused by the difference in the speed
of light in medium 1 and 2
Index of Refracti
Summary Lecture 17
Wavefronts and
Snells Law of Refraction
Smaller velocity
Wavefronts closer together
Change in direction
Refraction
Normal
1
Medium 1 (n1)
2
Medium 2 (n2)
Caused by the difference in the speed
of light in medium 1 and 2
Index of Refracti
Summary Lecture 16
Summary Lecture 16
Optical Instruments alter the
th
light-path and trick the eye into
seeing an image of an object at
seeing an image of an object at
a different location and with
different size
Mirrors
Law of Reflection
of Reflection
I
Summary Lecture 14
Waves
Amplitude
x
Wavelength
Waves are periodic in space (wavelength)
and time (Period T = 1/frequency)
time (Period
1/frequency)
Waves transport energy.
Wave velocity
velocity
v = f
Transverse waves:
Oscillation perpendicular to wave
Faradays Law of
Induction
Magnetic flux = A B cos
B
A
A changing magnetic flux
generates an induced voltage
(emf = electromotive force)
= (ABcos )final (ABcos )initial
V = [emf] = - N / t
Motional EMF
Voltage induced in a moving
conductor
Velocity
Vmax =
Faradays Law of
Induction
Induction
Magnetic flux = A B cos
B
A
A changing magnetic flux
generates an induced voltage
an induced voltage
(emf = electromotive force)
= (ABcos )final (ABcos )initial
(AB
V = [emf] = - N / t
[emf]
Motional EMF
Voltage induce
Summary Lecture 12
Summary Lecture 12
Force between parallel wires
Force between parallel wires
0I1I2
F/l =
2d
Force per
per
length
Distance
Parallel currents
Attractive
Anti - Parallel
currents
currents
Repulsive
Repulsive
Ampere Law:
Amperes Law:
electr
Normalization: +/- 0 (3:30, 4:30)
Summary Lecture 11
Magnetic Fields are caused by moving
Fields are caused by moving
charges (charged particles, current)
A fundamental law (Amperes Law)
connects B and I
Special cases
Long, straight wire
B = 0/2 I/r
Cente
Summary Lecture 10
Force on a moving charge in a
magnetic field
F = qvB sin
Velocity
Angle between
v and B
Fv in a constant magnetic field a
fi
charged particle travels on a circular path.
ev
F = ma
ma
qvB = mv2/r
mv
r = qB
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Summary Lecture 9
Magnetism
Magnets exert forces on certain
materials (e.g. iron)
Magnetic north and south pole
north and south pole
opposite poles attract
equal poles repel
poles repel
Field force
Magnetic field
Fieldlines go from N to S
go from to
No i
Summary Lecture 7
Ohms Law
V = ItotRtot
Series Circuits
Circuits
current is the same
through all elements
Itot = I1 = I2
V = V1 + V2
R = R 1 + R2
V1 = Itot R1 = R1/Rtot V
V2 = Itot R2 = R2/Rtot V
R1
V
R2
Parallel Circuits
Circuits
same voltage across
all
Summary Lecture
Summary Lecture 6
Dielectric
Inserting an insulator - a dielectric - into the
gap of a capacitor increases the capacitance
C
kC or A/d
k A/d
Energy stored in a capacitor
PE
1
=2
Battery
eZn2+
QV =
QV
Zn
1
2
CV2
CV
1
2
= Q2/C
Cu
Electrodes
Physics 112 Help
Wednesdays Recitation will
focus more on your questions.
More help & tutoring.
If you need more one-on-one
you need more one
help use this link to see a list
of tutors (physics grad
students)
http:/tiny.cc/tutors
Review session next wee
Summary
Summary Lecture 4
Mechanics
Electricity
Energy is conserved
Only differences in Potential Energy: PE
differences in Potential Energy:
+
PE = mgh
mgh
PE = ?
?
= Mass x Potential
= Charge x Potential
=qV
Electric Potential V = PE/q
Potential Differe
Summary Lecture
Summary Lecture 3
Charge
Charge
Electric Field
Electric Field
Electric Field
Field
E=
Force
F
q
Direction of E = Direction of F on positive test charge
Fieldlines:
direction of electric field (path of
away from + toward never cross
|E| can
Summary Lecture
Summary Lecture 2
Charge
Charge
Electric Field
Electric Field
Electric Field
Field
Force
F
E=
q
Direction of E = Direction of F on
positive test charge
Field of a point charge:
Q
E=k 2
r
Solving Problems
with Charges
with Charges
Drawing
Summary Lecture
Summary Lecture 1
The electric force is a field force
All electric effects are caused by
(electric) CHARGES
(electric) CHARGES
Atomic View:
Electrons and Protons carry an equal
but opposite charge
Elementary Charge:
e = 1.6 x 10-19 C (Coul
The following is a Physics 112 final exam from several years ago.
Please note that the syllabus has changed over the years and that this exam
includes topics we didnt discuss (for example, circuits with capacitors in series)
and some topics we talked abou
The following is a Physics 112 final exam from several years ago.
Please note that the syllabus has changed over the years and that this exam
includes topics we didnt discuss (for example, circuits with capacitors in series)
and some topics we talked abou
PHYSICS 112 FIRST LIIDTE'RM EXAM - April 22, 1992 9 AM Scon
me. Pelz . I
6
_ .Make sure to put your name and your recitation instructor's name on each page of the exam.
This is a closed book exam: calculators are allowed, but no formula sheet. The exam