Physics 2102

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Physics 2102

• Exam 2 Review Session
• Chapters 24.9-28.8 / HW04-06

Some links on exam stress http//appl003.lsu.edu/
slas/cas.nsf/Content/StressManagementTip1 http
//wso.williams.edu/orgs/peerh/stress/exams.html h
ttp//www.thecalmzone.net/Home/ExamStress.php http
//www.staithes.demon.co.uk/exams.html
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Exam 2

• (Ch24) Sec.11 (Electric Potential Energy of a
  System of Point Charges) Sec.12 (Potential of
  Charged Isolated Conductor)
• (Ch 25) Capacitors capacitance and capacitors
  caps in parallel and in series, dielectrics
  energy, field and potential in capacitors.
• (Ch 26) Current and Resistance current, current
  density and drift velocity resistance and
  resistivity Ohms law.
• (Ch 27) Circuits emf devices, loop and junction
  rules resistances in series and parallel DC
  single and multiloop circuits, power RC
  circuits.
• (Ch 28) Magnetic Fields FvxB, Right Hand Rule,
  Circular Motion, Force on Wire, Magnetic Dipole.

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Potential V of Continuous Charge Distributions
Straight Line Charge dq?dx ?Q/L Curved Line
Charge dq?ds ?Q/2?R Surface Charge
dq?dA ?Q/?R2 dA2?RdR
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Potential V of Continuous Charge Distributions
Curved Line Charge dq?ds ?Q/2?R
Straight Line Charge dq?dx ?Q/L
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Potential V of Continuous Charge Distributions
Surface Charge dq?dA ?Q/?R2 dARdRd?
Straight Line Charge dq?dx ?bx is given to you.
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Capacitors
E s/e0 q/Ae0 E V d q C V
C e0A/d
Connected to Battery VConstant Disconnected
QConstant
Ce0ab/(b-a)
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Current and Resistance
i dq/dt
R rL/A
Junction rule
r r0(1a(T-T0))
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DC Circuits
Loop rule
V iR P iV
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Resistors and Capacitors

• Resistors
  Capacitors
• Key formula ViR
  QCV
• In series same current same
  charge
• Req?Rj
  1/Ceq ?1/Cj
• In parallel same voltage same
  voltage
• 1/Req ?1/Rj
  Ceq?Cj

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Capacitors and Resistorsin Series and in
Parallel

• Whats the equivalent resistance (capacitance)?
• Whats the current (charge) in each resistor
  (capacitor)?
• Whats the potential across each resistor
  (capacitor)?
• Whats the current (charge) delivered by the
  battery?

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RC Circuits
Time constant RC
i(t)dq/dt
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Capacitors Checkpoints, Questions
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Problem 25-21
When switch S is thrown to the left, the plates
of capacitor 1 acquire a potential V0. Capacitors
2 and 3 are initially uncharged. The switch is
now thrown to the right. What are the final
charges q1, q2, and q3 on the capacitors?
Series
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Series
Seri-Q
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Current and Resistance Checkpoints, Questions
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Problem 26-56

• A cylindrical resistor of radius 5.0mm and length
  2.0 cm is made of a material that has a
  resistivity of 3.5x10-5 Wm. What are the (a)
  current density and (b) the potential difference
  when the energy dissipation rate in the resistor
  is 1.0W?

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Circuits Checkpoints, Questions
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Problem 27.P.018. 406649 Figure 27-33 shows
five 5.00 resistors. (Hint For each pair of
points, imagine that a battery is connected
across the pair.) Fig. 27-33 (a) Find the
equivalent resistance between points F and
H. (b) Find the equivalent resistance between
points F and G.
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Problem 27.P.046. 406629 In an RC series
circuit, E 17.0 V, R 1.50 M?, and C 1.80
µF. (a) Calculate the time constant. (b) Find
the maximum charge that will appear on the
capacitor during charging. (c) How long does it
take for the charge to build up to 10.0 µC?
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Magnetic Forces and Torques
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(28-13)
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(28-14)
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Ch 28 Checkpoints and Questions
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Circular Motion
Since magnetic force is perpendicular to motion,
the movement of charges is circular.
r
In general, path is a helix (component of v
parallel to field is unchanged).
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.
electron
Radius of Circlcular Orbit
.
C
r
Angular Frequency Independent of v
Period of Orbit Independent of v
Orbital Frequency Independent of v
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Problem 28.P.024. 566302 In the figure below,
a charged particle moves into a region of uniform
magnetic field , goes through half a circle, and
then exits that region. The particle is either a
proton or an electron (you must decide which). It
spends 160 ns in the region. (a) What is the
magnitude of B? (b) If the particle is sent
back through the magnetic field (along the same
initial path) but with 3.00 times its previous
kinetic energy, how much time does it spend in
the field during this trip?
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