# 2002 Exam 3

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1. What is the fundamental quantity for EM and what is the standard unit?
Electric Charge - Coulomb, C
2. Where do negative and positive charge reside?
• Positive - Nucleus
• Negative - Orbiting
3. How many charges are in one Coulomb? What is the charge in C on one proton or electron?
• 1C = 6.25x10^18 e/p
• 1e/p = 1.6x10^-19 C
4. What is the Law of Charges?
• Like charges repel
• Unlike charges attract
• -,- push}
• +,+ pull} Force
5. What is Coulomb's Law? Which force is greater: gravity or the EM force?
In words: The force between any two electrically charged objects is proportional to the product of their charges divided by the square of the distance between them.

• F = K q1 q2
• ___________ = N
•           r2
6. What is electric current? What is the unit?
• Electric current - charge in motion
• Unit - Ampere, A
7. What materials allow the flow of charges and which impede the flow of charge?
• Conductors allow the flow of charge. (metals, silver, copper)
• Insulators impede the flow of charge. (glass, plastic, rubber)
8. What is a semiconductor?
A substance, usually a solid chemical element conduct electricity under some conditions, but not others. (Ex. Graphite)
9. What happens when I separate charges? What is electric potential energy?
Work is done, W = F x d, when the charges are held in place it creates electric potential energy

Energy is applied on the system = Electric potential energy in Joules
10. What is voltage? What is its relationship to electric potential energy?
The pressure produced by an energy source in a circuit.

• Electric potential difference - By definition, the electric potential difference is the difference in electric potential (V) between the final and the initial location when work is done upon a charge to change its potential energy.
• Work / charge = J/c =Volt, V
11. What is the unit for voltage?
Volts, V
12. Explain what resistance is. What materials offer low resistance?
The quantity that measures how hard it is to push electrons through wires.

Copper / Silver / Aluminum offer low resistance
13. What is Ohm's Law? What is the relationship between current, voltage and resistance?
In words: The current in circuits is directly proportional to the voltage and inversely proportional to the resistance. The higher the electrical “pressure,” the higher the flow of charge. The higher the resistance to flow, the smaller the flow.

V = I x R / I = V / R
14. If voltage goes up and resistance is the same, what happens to the current?
The current increases.
15. If resistance goes up and voltage is the same, what happens to the current?
The current decreases.
16. What is the unit of resistance?
R = Ohms
17. What is an electric circuit?
The flow of an electric charge / charge in motion
18. What happens if a circuit is not a closed loop?
No work is being done, and the current cannot flow
19. Explain what happens when a battery is connected to a light bulb in a circuit?
The current flows into the bulb where energy is used and emits light.
20. Where does the energy for a circuit come from?
Come from a power source (mother battery) - battery, plant, etc
21. Where is the energy used in a circuit?
Resistance - remember the little green dudes
22. Why is the direction of current different than the direction of the flow of electrons?
Remember the battery and original flow versus later finding out that electrons flow the other way.
23. What are the different ways to express electric power?
• P = IV
• P = I^2R
• P = V^2/R (WATTS)
24. What is the difference between a series and parallel circuit?

How is the equivalent resistance of a series circuit determined?

How is the equivalent resistance of a parallel circuit determined?
Rs = R1 + R2 + R3 / I = V / Rs

1/Rp = 1/R1 + 1/R2 + 1/R3 / I = V/Rp (Inverse key twice to get answer)
25. When there are three increasing resistances (for example: 10ohms, 20ohms, 30ohms) connected in a parallel, how much of the current goes through each resistance?
Half if the same / but more current goes through the path of least resistance
26. If the resistances are all the same in a parallel circuit, how much current goes through each resistance?
The same amount for each.
27. What is the most sensible way to wire Christmas tree lights?
Parallel circuit
28. What is a pole of a magnet? What is the Law of Poles?
• Positive North Pole
• Negative South Pole

• Like poles repel
• Unlike poles attract
29. How can I detect the magnetic field?
Using a compass
30. What does a magnetic field of a bar magnet look like?
Remember her drawing - rounded on top / lines out the ends
31. What is the relationship between electric current and magnetism?

What does Maxwell's Equations tell us about the relationship between current and magnetism?
Charge in motion produces a magnetic field

Moving charges create a magnetic field / changing magnetic field creates an electric current
32. What does a magnetic field of a coil of wire look like?
Remember the drawing - rounded on top / lines out the end
33. What kinds of materials can form a permanent magnet?
Ferromagnetic - Iron, Nickel, Cobalt
34. What is the Curie Temperature?
Heat - 770*C where magnetism changes directions - remember the arrow drawing around nucleus
35. Why do we get different measurements of speed in different reference frames?
Because very observer's point of view is different / which can provide different accounts to the same event.
36. What is an inertial reference frame?
Newton's 1st Law is true / at rest, or in motion with constant velocity
37. What is Newtonian relativity?
No reference frame is superior to any other / The measure of space and time are absolute.
38. What did Maxwell's equations predict about the speed of light? Why was this a problem?
(speed of light) c = 3 x 10^8 m/s

Ball vs. Flashlight

Problem - free-fall vs. projectile motion
39. What is the ether? Why was it rejected?
Ether - reference frame at rest

No ether = new explanation - special relativity
40. What are the postulates of special relativity?
Postulate 1 - laws of physics are the same in any inertial reference frame

Postulate 2 - Light (EM waves) propagates through vacuum at speed c regardless of the speed of the source or receiver (observer).
41. Why can two observers in different reference frames experience events differently?
The universe we live in possesses this general feature—different observers will describe the same event indifferent terms, depending on their frames of reference. (Ex. Train - in book)
42. What is time dilation?
is an actual difference of elapsed time between two events as measured by observers either moving relative to each other or differently situated from gravitational masses. (moving clocks slow down)
43. What is length contraction?
only occurs in the direction of motion
44. What happens to mass as speed increases?
Mass increases as speed increases
45. What is the relationship between mass and energy?
Mass and energy are interchangeable
46. What are the main conclusions of special relativity?
47. Do I have to worry about relativistic effects in my normal day-to-day life? Why or why not?
48. What is the history of the development of the idea of the atom?
In about 530 BC, a group of Greek philosophers, the most famous of whom was a man named Democritus, gave this question some serious thought. Democritus argued (purely on philosophical grounds) that if you took the world’s sharpest knife and started slicing chunks of matter, you would eventually come to a smallest piece—a piece that could not be divided further. He called this smallest piece the “atom,”which translates roughly as “uncuttable.”

• Remember the Gold - Infinite # of times
• Finite # of times -> Democritus
49. Who are the important people in this history and what contributions did they make?
John Dalton (Atomic Theory) - "Billiard Ball Model" ie - solid mass (around 1800)

JJ Thomson - 1897 discovered electrons (negative particle) "Plum Pudding Model" dots where negative, solid positive

Rutherford - 1910 "Nuclear Model" 99.9% of mass positive / nothing but empty space He atoms through Gold Foil
50. What is ultraviolet catastrophe? How did Max Planck explain it? What does it mean that energy is quantized?
it diverges as; this divergence for high frequencies is called the ultraviolet catastrophe. Infrared - red - orange - yellow - blue - indigo -violet - UV -> energy

"Quantized Energy" - can't stand anywhere in between (remember the stairs) E=hf
51. What contribution did Einstein make?
EM can talk about it as a PARTICLE -> photon (light)

They carried E=hf

Wave-Particle Duality
52. When is light a wave and when it is a particle?
Just depends on the circumstance. (what she said in class)
53. What was the Bohr atom?
"Planetary Model" - where the electrons absorb energy and emit energy. (remember the drawing in class)

Ground state - lowest possible level electrons can exist.

Excited state - absorb energy (photon)
54. What is the bright light spectra?
Remember the poster she brought to class pg. 172 in book
55. In what way was Bohr's atom a violation of classical physics?
Accelerating charges radiate energy.
56. What happens to an electron when it absorbs a photon?
Excited state - quantum leap
57. What is a quantum leap?
When a electrons absorb energy and jumps to a higher level in the atom
58. What happens when a electron emits a photon?
It returns to its previous level.
59. What is ionization?
where a electron has jumped free from the atom.
60. What was the problem with Bohr's model?
He used Hydrogen atom / one electron.  Didn't work for any other atom element.
61. How did DeBroglie solve the problem?
Electrons have wave properties.
62. What is the DeBroglie wavelength?
delta symbol = h/mv

Orbitals

Wave shapes - only certain waves shapes are allowed.
63. What are the four principal quantum numbers?
Principal Quantum #- n=1,2,3,4....

Orbital Quantum # - l = 0,1,2,3...

Magnetic Quantum # - ml = -l to +l

Spin # - ms = - 1/2, +1/2
64. What is the Pauli Exclusion Principle?
No two electrons can have the same 4 quantum numbers.
65. What is the symbolism physicists use for orbitals? Chemist?
• Physicists - l=0, l=1, l=2, l=3, l=4....
• Chemist - s, p, d, f, g...
66. How many electrons can be in l=0,l=1,l=2,l=3 orbital?
2, 8, 18, 32...
67. What is electron configuration?
• 1s^1 - H
• 1s^2 - He
• 1s^2 2s^1 - Li
68. How can I tell how many electrons are in an atom if I have the electron configuration?
1s2 2s2 2p6 3s2 3p5 - 17 Electron - Cl

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 Author: JonJon2327 ID: 288143 Filename: 2002 Exam 3 Updated: 2014-11-05 22:20:03 Tags: Science Folders: Description: Exam 3 Show Answers:

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