Physics 202, Lecture 29
Review sessions
Today’s Topics
!  Final Exam Logistics
" Friday 5/7, 2pm, 2103 Chamberlin (Capecchi)
!  Review (I) – Chapters 21-28: Electrostatics, DC Circuits,
Magnetostatics, Faraday’s Law, AC Circuits
" Friday, 5/7, 4pm, 2103 Chamberlin (Kruse)
" Saturday 5/8, 1pm 2241 Chamberlin (Poudel)
!  Review questions available: follow links at
http://www.physics.wisc.edu/undergrads/courses/spring10/202/exams.htm
" Sunday 5/9, 3:30pm, 2241 Chamberlin (Pettus)
" Monday 5/10, 10:30am, 2241 Chamberlin (Lim)
Final Exam Logistics
" Exam Time: Monday, May 10, 5:05 pm – 7:05 pm
" Rooms:
165 Bascom: Sections 304, 305, 307, 310, 321,
322, 324, 325, 326, 330
(Capecchi, Garcia, Kruse, Lim, Pettus)
1310 Sterling: Sections 301, 302, 303, 308, 309,
323, 327, 329
(Poudel, Rudinger, Santander, Stuart)
" Bring: calculator, ruler, self-prepared formula sheets
(3 single-sided 8.5” !11” sheets from previous midterms + 1
new 8.5” !11” single-sided sheet for new material)
Final Exam
" Coverage:
" 60% previous material (weighted more heavily
toward first 1/2 of course), and 40% new material
" Format: multiple-choice, similar to midterms 2 and 3
" This lecture’s review: chapters 21-28:
#  background, electrostatics, DC circuits,
magnetostatics, Faraday’s Law, AC circuits
Background Material
Mechanics:
You are responsible for anything that was asked of
you on homework or on midterm exams.
Kinematics of uniformly accelerated motion
Uniform circular motion, springs
Newton’s Laws: statics and dynamics
Work-kinetic energy theorem, conservation of energy
Math:
Vector algebra, scalar (dot) product, vector product
Calculus: differentiation, simple integration (1D only)
More Electrostatics Topics
More Topics (not exhaustive):
Point charges: Coulomb forces and potential energy
Motion of point charges in electric fields
(e.g., single particles, electric dipoles)
Electric field lines and equipotentials
Conductors in electrostatic equilibrium
Conductors and Gauss’ law
Capacitance, capacitors with dielectrics
Electrostatics Topics
Calculating electric fields and potentials for discrete and
continuous charge distributions.
3 methods:
1. Direct calculation of E field: integrate to get V.
2. Gauss’ Law: obtain E (special cases), integrate to get V.
3. Calculate electric potential V: take derivatives to get E.
You will not be asked to do nontrivial surface or volume
integrals. You may need to do simple 1-d integrals.
Example: linear charge distributions.
Example: Gauss’ Law (spherical, cylindrical, or planar
symmetry)
Resistors, Capacitors, DC Circuits
Main topics:
Simplifying resistor or capacitor networks
Using Kirchhoff’s circuit laws
Also:
Definition of resistance and capacitance
Ohm’s law
Electromotive force
Real and ideal batteries
Energy in capacitors
Power in circuits
Magnetostatics Topics
" Calculating magnetic fields for current distributions
" Response of charges to external magnetic fields
Two methods for calculating magnetic field:
1. Biot-Savart law: direct method
2. Ampere’s law: for special cases with high
symmetry
More Magnetostatics Topics
" Forces on moving charged particles, magnetic
dipoles, and current distributions in external
magnetic fields
" Torque on magnetic dipoles
" Lorentz force law
Recall direction – right-hand rule(s)
Bio-Savart: linear current distributions – finite wire,
current loop, current arc.
Ampere’s law: solenoid, toroid, infinite thin wire,
infinitely long wire of finite radius with current
distribution in interior of wire.
" Moving charges in uniform B field: helical motion
Charges Q1 = –q and Q2 = +4q are placed as
shown. At which of the five positions
indicated by the lettered dots might the
electric field be zero?
Charges Q1 = –q and Q2 = +4q are placed as
shown. At which of the five positions
indicated by the lettered dots might the
electric field be zero?
" Applications:
#  Velocity Selector
#  Mass Selector
#  Hall Effect
Two electric dipoles, p1 and p2, are arranged as shown.
The first dipole is not free to rotate but the second
dipole can rotate in any direction. Which way will p2
rotate? The directions represent the following:
1 – clockwise, 2 – counter-clockwise, 3 – rotate about
axis of the dipole rolling up, and 4 – rotate about axis of
the dipole rolling down.
Two electric dipoles, p1 and p2, are arranged as shown.
The first dipole is not free to rotate but the second
dipole can rotate in any direction. Which way will p2
rotate? The directions represent the following:
1 – clockwise, 2 – counter-clockwise, 3 – rotate about
axis of the dipole rolling up, and 4 – rotate about axis of
the dipole rolling down.
A.  1
A.  1
B.  2
B.  2
C.  3
C.  3
D.  4
D.  4
E.  None of these is correct.
E.  None of these is correct.
The figure shows a surface
enclosing the charges 2q and –q.
The net flux through the surface
surrounding the two charges is
The figure shows a surface
enclosing the charges 2q and –q.
The net flux through the surface
surrounding the two charges is
Charges +Q and –Q are arranged at the
corners of a square as shown. When the
magnitude of the electric field E and the
electric potential V are determined at P, the
center of the square, we find that
Charges +Q and –Q are arranged at the
corners of a square as shown. When the
magnitude of the electric field E and the
electric potential V are determined at P, the
center of the square, we find that
A.  E ! 0 and V > 0.
A.  E ! 0 and V > 0.
B.  E = 0 and V = 0.
B.  E = 0 and V = 0.
C.  E = 0 and V > 0.
C.  E = 0 and V > 0.
D.  E ! 0 and V < 0.
D.  E ! 0 and V < 0.
E.  None of these is correct.
E.  None of these is correct.
The figure depicts a uniform electric field.
Along which direction is there no change in
the electric potential?
The figure depicts a uniform electric field.
Along which direction is there no change in
the electric potential?
If C1 < C2 < C3 < C4 for the combination of
capacitors shown, the equivalent
capacitance is
If C1 < C2 < C3 < C4 for the combination of
capacitors shown, the equivalent
capacitance is
A.  less than C1.
A.  less than C1.
B.  more than C4.
B.  more than C4.
C.  between C1 and C4.
C.  between C1 and C4.
If a dielectric is inserted between the plates
of a parallel-plate capacitor that is
connected to a 100-V battery, the
If a dielectric is inserted between the plates
of a parallel-plate capacitor that is
connected to a 100-V battery, the
A.  voltage across the capacitor decreases.
A.  voltage across the capacitor decreases.
B.  electric field between the plates decreases.
B.  electric field between the plates decreases.
C.  electric field between the plates increases.
C.  electric field between the plates increases.
D.  charge on the capacitor plates decreases.
D.  charge on the capacitor plates decreases.
E.  charge on the capacitor plates increases.
E.  charge on the capacitor plates increases.
You want to use a metal bar as a resistor.
Its dimensions are 2 by 4 by 10 units. To
get the smallest resistance from this bar,
you should attach leads to the centers of two
opposite sides that have the dimensions of
You want to use a metal bar as a resistor.
Its dimensions are 2 by 4 by 10 units. To
get the smallest resistance from this bar,
you should attach leads to the centers of two
opposite sides that have the dimensions of
A.  2 by 4 units.
A.  2 by 4 units.
B.  2 by 10 units.
B.  2 by 10 units.
C.  4 by 10 units.
C.  4 by 10 units.
Which of the following relations among the
quantities in the figure is generally correct?
Which of the following relations among the
quantities in the figure is generally correct?
A.  I1R1 = I2R2
A.  I1R1 = I2R2
B.  I3R3 = I4R4
B.  I3R3 = I4R4
C.  I1R1 = I4R4
C.  I1R1 = I4R4
D.  I3R4 = I4R3
D.  I3R4 = I4R3
E.  I1R1 + I2R2 = !
E.  I1R1 + I2R2 = !
Electrons travel at an initial velocity v0. They pass
through a set of deflection plates, between which
there exists an electric field which deflects them
upwards toward point b. In which direction should a
magnetic field be applied so that the electrons land
undeflected at a?
Two very long, parallel conducting
wires carry equal currents in the
same direction, as shown. The
numbered diagrams show end
views of the wires and the
resultant force vectors due to
current flow in each wire. Which
diagram best represents the
direction of the forces?
Electrons travel at an initial velocity v0. They pass
through a set of deflection plates, between which
there exists an electric field which deflects them
upwards toward point b. In which direction should a
magnetic field be applied so that the electrons land
undeflected at a?
Two very long, parallel conducting
wires carry equal currents in the
same direction, as shown. The
numbered diagrams show end
views of the wires and the
resultant force vectors due to
current flow in each wire. Which
diagram best represents the
direction of the forces?
A copper ring lies in the yz plane as
shown. The magnet's long axis lies along
the x axis. Induced current flows through
the ring as indicated. The magnet
A copper ring lies in the yz plane as
shown. The magnet's long axis lies along
the x axis. Induced current flows through
the ring as indicated. The magnet
A.  must be moving away from the ring.
A.  must be moving away from the ring.
B.  must be moving toward the ring.
B.  must be moving toward the ring.
C.  must remain stationary to keep the
current flowing.
C.  must remain stationary to keep the
current flowing.
Final Words of Advice
" Read all the questions – some are much harder than
others, and they are not in order of difficulty.
" Recall that EM forces are typically not constant –
they usually depend on position. Only in rare
situations (inside parallel plate capacitor or long
solenoid) are E and B uniform.
#  Moral – Beware of using forces rather than energy
conservation to solve problems – the kinematics
of uniformly accelerated motion rarely applies
" Remember: units, vector magnitude and direction