lecture 31: mon 30 mar review session : midterm 3 physics 2113 jonathan dowling

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Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

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Page 1: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

Lecture 31: MON 30 MARReview Session : Midterm 3

Physics 2113

Jonathan Dowling

Page 2: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

EXAM 03: 8PM MON 30 MAR in Cox Auditorium

The exam will cover: Ch.26 through Ch.29The exam will be based on: HW07 – HW10.

The formula sheet for the exam can be found here:http://www.phys.lsu.edu/classes/fall2014/phys2113/downloads/FormulaSheetTest3.pdf

You can see examples of old exam IIIs here:http://www.phys.lsu.edu/faculty/gonzalez/Teaching/Phys2102/Phys2102OldTests/

Page 3: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

Current and ResistanceCurrent and Resistancei = dq/dt

V = i RE = J ρ

ρ = ρ0(1+(TT0))

R = ρL/AJunction rule

Page 4: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

Current and ResistanceCurrent and Resistance

Page 5: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

Current and Resistance: Checkpoints, QuestionsCurrent and Resistance: Checkpoints, Questions

Page 6: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

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 Ωm. What are the (a) current density and (b) the potential difference when the energy dissipation rate in the resistor is 1.0W?

Page 7: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling
Page 8: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

CircuitsCircuitsi = dq/dt

Junction rule

Page 9: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

DC CircuitsDC Circuits

Single loop Multiloop

V = iRP = iV

Loop rule

Page 10: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

Resistors vs CapacitorsResistors vs Capacitors

Resistors Capacitors

Key formula: V=iR Q=CV

In series: same current same charge

Req=∑Rj 1/Ceq= ∑1/Cj

In parallel: same voltage same voltage

1/Req= ∑1/Rj Ceq=∑Cj

Page 11: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

ResistorsResistorsin Series and in Parallelin Series and in Parallel

• What’s the equivalent resistance?• What’s the current in each resistor? • What’s the potential across each resistor?• What’s the current delivered by the battery?• What’s the power dissipated by each resisitor?

Page 12: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

Series and Parallel

Page 13: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

Series and Parallel

Page 14: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

Series and Parallel

Page 15: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling
Page 16: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

Circuits: Checkpoints, QuestionsCircuits: Checkpoints, Questions

Page 17: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

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.Slide Rules:

You may bend the wires but not break them.

You may slide any circuit element along a wire so long as you don’t slide it past a three (or more) point junction or another circuit element.

Page 18: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling
Page 19: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

Problem: 27.P.046. [406629]

In an RC series circuit, E = 17.0 V, R = 1.50 MΩ, 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 16.0 µC?

Page 20: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling
Page 21: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

Magnetic Forces and TorquesMagnetic Forces and Torques

L

vF

Page 22: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

C

C

Top viewSide view

(28-13)

Page 23: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

(28-14)

Page 24: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

Ch 28: Checkpoints and QuestionsCh 28: Checkpoints and Questions

Page 25: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

Circular Motion: Since magnetic force is perpendicular to motion, the movement of charges is circular.

B into blackboard.

v

F

In general, path is a helix (component of v parallel to field is unchanged).

In general, path is a helix (component of v parallel to field is unchanged).

r

Page 26: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

.

.electron

C

r

Radius of Circlcular OrbitRadius of Circlcular Orbit

Angular Frequency:Independent of v Angular Frequency:Independent of v

Period of Orbit:Independent of v Period of Orbit:Independent of v

Orbital Frequency:Independent of v Orbital Frequency:Independent of v

Page 27: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling
Page 28: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

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?

Page 29: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling
Page 30: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

Highest Torque: θ = ±90° sinθ = ±1

Lowest Torque: θ= 0° & 180° sinθ = 0

Bθ = 180°–cosθ = +1

θ = 0°–cosθ = –1

Page 31: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling
Page 32: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling
Page 33: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling
Page 34: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling
Page 35: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

Right Hand Rule: Given Current i Find Magnetic Field B 

Page 36: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

Checkpoints/QuestionsCheckpoints/QuestionsMagnetic field?

Force on each wire due to currents in the other wires?

Ampere’s Law: Find Magnitude of ∫B∙ds?

Page 37: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

The current in wires A,B,D is out of the page, current in C is into the page. Each wire produces a circular field line going through P, and the direction of the magnetic field for each is given by the right hand rule. So, the circles centers in A,B,D are counterclockwise, the circle centered at C is clockwise. When you draw the arrows at the point P, the fields from B and C are pointing in the same direction (up and left).

Right Hand Rule: Given Current i Find Magnetic Field B 

Page 38: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling

A length of wire is formed into a closed circuit with radii a and b, as shown in the Figure, and carries a current i.

                                           

(a) What are the magnitude and direction of B at point P?                                            

(b) Find the magnetic dipole moment of the circuit.                                                

μ=NiA

Right Hand Rule & Biot-Savart: Given i Find B 

Page 39: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling
Page 40: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling
Page 41: Lecture 31: MON 30 MAR Review Session : Midterm 3 Physics 2113 Jonathan Dowling