Instructional Objectives for Third Exam***
Physics 2220, Spring 2013
Chapters (Skip 28), 29, 30, 31
Material that will not be included on the third exam is indicated with "skip".
Skip 1. Understand and be able to derive Equation 28.1 for the relationship between peak and rms values for
1/2 sinusoidal functions. Eg. V rms
=V p
/2
Skip 2. Be able to use capacitive and inductive reactance and impedance in comparison with Ohm's law resistance.
Section 28.2 and 28.4, Eqs. 28.7, 28.8, and 28.12. Z=[R
2
+(X
C
-X
L
)
2
]
1/2
X
C
=1/ωC X
L
=ωL
V=IX
3. There will be no exam questions on phasors.
4. Be able to use the equation for resonant frequency in an LC circuit – Eq. 28.10.
ω resonance
=1/(LC)
1/2
Skip 5. Understand the material in Section 28.4, Driven RLC Circuits and Resonance. The exam won't have questions about phase angle, Eq. 28.13.
2
6. Understand Maxwell's contribution to Ampere's Law (addition of displacement current) and why the set of
I equations, 29.2-29.5 is given his name (because with it the equations describe electromagnetic radiation). d
=ε
0 dΦ
E
/dt
E
7. Be able to describe from memory plane electromagnetic waves in empty (free) space including Eqs. 29.10, 29.11,
29.16 a,b,c, and 29.17. Memorize the general feature of all sources of electromagnetic waves (accelerating electric charge). E = E
0 j sin(kx-ωt) B= B
0 k sin(kx-ωt) or use sin2π(x/λ-t/T)
E
0
=cB
0
c=ω/k = λ/T ω=2πf k=2π/λ f=1/T
8. Understand polarization.
9. Understand Fig. 29.10 describing the electromagnetic spectrum. Be able to rank from memory in terms of increasing frequency (or decreasing wavelength) the following waves: whistlers, radio, microwave, infrared, visible, ultraviolet, and x rays (and gamma rays). Understand a typical frequency of "whistlers". Understand why x rays and gamma rays share the same portion of the spectrum, contrary to the figure in the book (both have unlimited upper frequencies.). ( Skip) Understand the difference between line-spectrum x rays and bremsstrahlung.
Understand dental x rays and class stories about them.
10. Know the following: Hertz is credited with the "first brilliant" confirmation of Maxwell's theory and therefore
"cycle per second" is given his name. It wasn't the first contribution, but it was certainly "brilliant". He died when he was 37. The first actual confirmation was made by an English dentist D. E. Hughes*.
11. On intensity, radiation pressure, and Poynting's Vector S understand and be able to use Eqs. 29.19, 20, 21, and skip ( 22 and that radiation carries momentum per unit area per unit time S/c ).
S = E x B
/μ
0
Plane Wave S=EB/μ
0
S average
=S peak
/2 (Skip) Pressure = S/c
12. Understand and be able to use Eqs. 30.1, 2, and 3 concerning reflection at a boundary, the index of refraction, and Snell's Law. From Snell's Law be able to derive the angle for total internal reflection and understand examples and consequences of this including fiber optics. n=c/v n
1 sinθ
1
=n
2 sinθ
2
1/s + 1/s’ = 1/f

13. Understand dispersion and how this helps account for rainbows.
14. Understand and be able to use, for a converging lens, the lens equation, Eq. 31.5. Be able to draw diagrams using ray tracing.
15. Be able to explain how converging and diverging lenses compensate for defects in the eye. Understand
"nearsighted" and "farsighted". See Figs. 31.28, 29.
* David Edward Hughes (1831-1900) An experimental physicist with little mathematical training. In 1879
Hughes managed to transmit and receive electromagnetic waves over a distance of several hundred metres using a detector made of a piece of coke resting on a bright steel contact. He observed that a loose contact between metal particles performed as well but tended to ‘Coher’ after use and needed to be tapped to loosen them before the next signal. He also found that “sudden electric impulses” work best as electro-magnetic waves. Unfortunately the scientific community refused to accept his work saying it was merely electromagnetic induction and he was wrong in his assumption that he was radiating Maxwell’s waves; he ceased working on the project and the results were not published until 1889. What he had done was later finally acknowledged in 1900.
**Hertz did not realize the practical importance of his experiments. He stated that," It's of no use whatsoever [...] this is just an experiment that proves Maestro Maxwell was right—we just have these mysterious electromagnetic waves that we cannot see with the naked eye. But they are there.
"
[8][9][10]
Asked about the ramifications of his discoveries,
Hertz replied," Nothing, I guess ."
*** A page of equations will appear on the exam.
Useful Equations for Third Exam
Chapters 28, 29, 30, 31
Z=[R
2
+(X
C
-X
L
)
2
]
1/2
X
C
=1/ωC X
L
=ωL V=IX where X represents R , X
C
, X
L
, or Z
.
ω resonance
=1/(LC)
1/2
V rms
=V p
/2
1/2
I rms
=I p
/2
1/2
I d
=ε
0 dΦ
E
/dt
E
E = E
0 j sin(kx-ωt) B= B
0 k sin(kx-ωt) or use sin2π(x/λ-t/T)
E
0
=cB
0
c=ω/k = λ/T ω=2πf k=2π/λ f=1/T
S = E x B /μ
0
Plane Wave S=EB/μ
0
S average
=S peak
/2 Pressure = S/c n=c/v n
1 sinθ
1
=n
2 sinθ
2
1/s + 1/s’ = 1/f
=-dФ
B
/dt