Final Review Preparationfor the final exam Preparation for the final exam.
Phys 102 – Lect. 29 Final exam review 1. Final exam study approaches How should you study for the...
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Transcript of Phys 102 – Lect. 29 Final exam review 1. Final exam study approaches How should you study for the...
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Phys 102 – Lect. 29Final exam review
Final exam study approaches
How should you study for the physics exam?• Cramming DOES NOT work• Emphasize understanding concepts & problem solving,
NOT memorization• Review pre-lecture & lecture concepts• Review problems: ACTs, HW, quizzes, practice exams• Understand formula sheet (i.e. when to use and when NOT
to use an eq.) & know what each symbol means• Do practice exam problems (time yourself!)
Phys. 102, Review 29, Slide 2
Phys. 102, Review 29, Slide 3
Review lecture ACTs
70%
EX2
Some exam problems are inspired by ACTs.
30%
Review homework questions
Phys. 102, Review 29, Slide 4
20%!
EX2
Some exam problems are inspired by the HW.
100%
Problem solving approachesThe not-so-good approaches:
Conceptual understanding / reasoning from basic principles:
“Reasoning by analogy”/memorization:“I remember every time we’ve done RC circuit problems, VC = after a long time...”
1. The capacitor is fully charged, so IC = 0 2. Resistor R3 is in series with C so I3 = 03. But, current can flow around inner loop, so I1 > 0 4. Algebra! KLR: – I1R1 – VC = 0, therefore VC <
The good approach:
Phys. 102, Review 29, Slide 5
20%!
EX2
Problem solving approachesThe not-so-good approaches:
The “magic” equation:
Conceptual understanding / reasoning from basic principles:
“What equation will solve this problem?Req = R1+R2, V = IR?”
1. Redraw the circuit to make it clearer2. The rightmost resistor is shorted, so no current
flows through it!3. So, the current through the bottom resistor is I4. Algebra! KLR: E – IR = 0
The good approach:
Phys. 102, Review 29, Slide 6
EX2
70%
7
1. Electricity & circuitsLects. 1 – 9
Vector Number (“scalar”)
Property
of
interacting c
harges
Property
of
point in sp
ace
Ex:
Ex:Ex:
Ex:
F
E V
UE[N] [J]
[N/C]=[V/m] [J/C]=[V]
Relationship between F, E, UE, V
EV U qqE F
1 22
q qF k
r 1 2q q
U kr
2
qE k
r
qV k
rE points from
high to low V
cosE
E
W F r θU
Phys. 102, Review 29, Slide 8
Wire Battery
Circuits & componentsCapacitor Resistor
Series and parallelBasic principles:Conservation of charge (KJR) Conservation of energy (KLR)
21
1
2 Current In = Current Out
Sum of voltages around loop = 0
0V
in outI I
Phys. 102, Review 29, Slide 9
1 2 eqI I I
1 2 eqV V V 1 2 eqV V V 1 2 eqI I I
RC Circuits
Phys. 102, Review 29, Slide 10
Charging:Initially the capacitor is uncharged At t = 0 we close switch S1
0,0 0C
QV
C
After a long time (t = ):Charge on C builds and saturatesCurrent decreases to zero
,0 0CI
, 0C
QV
C
, 0CI
C acts like a wire
C acts like an open circuit
+ε
IC
R
S1
C
S2
+Q
–Q
Immediately after (t = 0):No charge on C yetCurrent IC,0 flows charge onto C
Discharging:Initially the capacitor is fully charged At t = 0 we close switch S2
Immediately after (t = 0):C still fully chargedCurrent IC,0 flows charge off of C
After a long time (t = ):Charge dissipates to zero Current decreases to zero
0,0 0C
QV
C ,0 0CI
, 0C
QV
C
, 0CI
C acts like a battery
C acts like an open circuit
11
2. MagnetismLects. 10 – 15
I
Type I: RHR for forces on moving charges and currents
Type II: RHR for magnetic fields generated by currents
I
I
Thumb along I
Curl fingers alongB
Curl fingers along I
Thumb alongB
B field from wire B field inside loop
vThumb along BFingers along
F on + q is out of palmF on – q is into palm
+q
F
B
OR:
v
I
F
–F
v
q
Moving + charges and currents Moving – charges
vThumb alongBFingers along
B
B
B
B
B
I I
Thumb along I
Curl fingers alongB
B
Magnetism summary
0
2wireμ I
Bπr
0solB μ nIsinF q vB θ sinF ILB θ
sinloopτ NIAB θ sinμB θPhys. 102, Review 29, Slide 12
1. Is increasing, decreasing, or constant?
2. If increases: ε induces B field opposite external B field
3. Type II RHR gives current direction
BindBind
Induced EMF ε opposes change in flux
Side viewTop view
Bind
Bext
Bext
If decreases:ε induces B field along external B field
Top view
Bext
Bind
Bext
Side view
If is constant:ε is zero, no induced B field
I
I
Curl fingers along IThumb along Bind
Bind
Bind
II
II
Lenz law
Phys. 102, Review 29, Slide 13
2. Magnetic field B
cosBA φ
εt
Since , 3 things can change F
Faraday’s law: “Induced EMF” = rate of change of magnetic flux
ε BLv ( ) sinε t ωNBA ωt
1. Area of loop 3. Angle φ
v
10 20t
B(t)
+1.0
-1.0
0
+0.5
-0.5
0
Bε A
t
BnωB
Faraday’s law
Phys. 102, Review 29, Slide 14
15
3. Light & opticsLects. 16 – 23
Light summary
Properties of electromagnetic wavesRelation between E, B, f, λEnergy density, power & intensityPolarization
Ray model of lightReflectionRefractionMirrorsLenses (alone, in combination)The eye (nearsightedness, farsightedness)
InterferenceConstructive and destructive interferenceDiffraction & resolution
Phys. 102, Review 29, Slide 16
20tot rms
PI c u cε E
A
2costrans incI I θ
i i
o o
h dm
h d
1 1 1
o if d d
i rθ θ1 1 2 2sin sinn θ n θ
Light as a wave (again)Interference: phase shift & path length difference
θ
θ
d
sind θ
θ
Constructive: phase shift of mλDestructive: phase shift of (m + ½)λ
Phase shift
sin md θ mλ
12sin ( )md θ m λ
Two & multiple slit maxima
Two slit minima
sin ma θ mλSingle slit minima
0, 1, 2...m
1, 2...m
1sin 1.22D θ λCircular aperture minimum Phys. 102, Review 29, Slide 17
Example: Interference
Phys. 102, Review 29, Slide 18
Extra practice
19
4. Modern physicsLects. 23 – 28
Quantum mechanics
Wave-particle dualityMatter waves – particle as a wave (de Broglie)Photons – light as a particle (photoelectric effect)
Bohr modelquantized orbits & energies, electronic transitions
Nuclear & particle physicsstructure of nucleus & nucleonsdecay processes (α, β, γ) & rates, binding energyquark model
hλ
p
2
0nn
r aZ
2
213.6eVn
ZE
n
Quantum modelquantum numbers (n, ℓ, mℓ, ms), Pauli exclusion principle, magnetic properties of atoms
Phys. 102, Review 29, Slide 20
Example: wave-particle duality
Phys. 102, Review 29, Slide 21
Extra practice
Example: quantum numbersExtra practice
Phys. 102, Review 29, Slide 22
Example: quantum atomExtra practice
Phys. 102, Review 29, Slide 23
Example: nuclear decayExtra practice
Phys. 102, Review 29, Slide 24