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Physics 7 > midterm II (sketch) > Flashcards

midterm II (sketch) Flashcards

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1
Q

Momentum is the “quantity of ______”

A

Motion

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2
Q

Mass is the “quantity of ______”

A

Inertia

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3
Q

Conservation of momentum equation for F?

A

(change)p/(change)t = F

if F=0, p=0 and momentum is conserved

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4
Q

Newtons second law (law of motion) and Newton’s law of universal gravitation equations?

A

Law of motion: F = ma

Newton’s universal law: F = G(m1m2/r^2)

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5
Q

p (momentum) = ______

A

mv

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6
Q

Neutron decay: a parent particle can’t decay to daughter particles if total daughter masses are ______?

A

> (greater than) the parent particle mass

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7
Q

The neutrino (“little neutral one”) was hypothesized to account for the ______. The neutrino was finally observed in 1956..

A

missing momentum in neutron decay

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8
Q

Angular momentum is the momentum of rotation. it takes torque to stop AM.

A

torque is easier to apply if the distance r from the center of rotation is farther (easier to close a door farther away from hinges)
L = rp = rmv

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9
Q

Torque =

A

(change)L/(change)t

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10
Q

Most classical knowledge was lost after fall of Rome 400 CE. Preserved in Arab writings. Reintroduced to Europe in 11th century.

A

x

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11
Q

Heliocentric vs. geocentrism: proponents

A

First done by Aristarchus of Samos. Then reintroduced by Copernicus. Aristotle and Ptolemy were for geocentrism.

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12
Q

What is an astronomical unit (AU)?

A

An AU is the distance from the center of the Earth to the center of the sun.

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13
Q

How long does it take light to travel 1 AU?

A

499 seconds

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14
Q

Brahe took Kepler as an apprentice. Kepler took Brahe’s data. The quality of the data was essential to Kepler’s work and success.

A

x

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15
Q

Mars’ orbit deviates 2nd most (after Mercury) from a circle

A

x

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16
Q

What makes a comet in the Kuiper Belt or Oort cloud change its orbit and enter the inner solar system?

A

It is gravitationally perturbed, or collided with, or both; then, the sun’s gravity pulls it in.

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17
Q

Why didn’t the asteroids in the asteroid belt between Mars and Jupiter coalesce to form a planet?

A

Jupiter’s gravitational influence was too strong for the asteroids to accrete.

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18
Q

Explain how Galileo’s observation of all the stages of the phases of Venus (new, waxing, full, waning) falsified the geocentric model of Aristotle and Ptolemy.

A

The sun cannot be between Earth and Venus if all of Venus’ phase stages can be observed.

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19
Q

Does Galileo’s observation of all the stages of phases of Venus falsify the Brahe’s geocentric model?

A

No, because all of Venus’ phase stages can be seen in this model.

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20
Q

In Newton’s particle theory of light, why does light travel faster in glass than in air?

A

Something about the perpendicular geometry made him wrong (?) [He thought light was being attracted according to his gravity theory, making it move faster?]

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21
Q

In Huygens’ theory of light, why does light travel faster in air than in glass?

A

He thought the speed of light decreased when passing from air to glass. [geometry? fuck.]

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22
Q

Explain how Foucault’s experiment with a rotating and stationary mirror could be used to test the speed of light in glass vs. air.

A

The angle made by the light path as it traveled to the fixed mirror and back through the water was larger than when the water was not present.

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23
Q

If light is a wave like sound, it should diffract. When can hear around corners, why can’t we see around corners. Does this mean light does not diffract?

A

No, light DOES difffract, but its wavelengths are too small to detect (compared to sound).

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24
Q

Why is the Earth’s magnetic north pole at the south geographic pole and vice versa?

A

By convention, magnetic field lines start at a north pole and end at a south pole. The magnetic field lines of Earth start at what we geographically call the south pole.

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25
Q

If a permanent magnet is broken in two, why are two permanent magnets created, and the north and south poles of the first magnet cannot be isolated?

A

Because when the magnet is severed, the magnetic domains remain oriented in the same direction, so one magnet becomes two with the same magnetic directions.

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26
Q

What are the requirements for a planet or star to have a magnetic field?

A

1) An interior with an electrically conductive liquid or gas

2) Significant movement of the charges, generating a current - by a) heat convection or b) significant rotational speed

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27
Q

Are there any moons in our solar system that have a magnetic field, and how is that field formed?

A

Yes, but their fields are very weak… (?)

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28
Q

Does Venus have aurora’s like Earth?

A

No, Venus’ magnetic field is not strong enough to produce auroras like with Jupiter and Earth.

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29
Q

What is the average magnetic field strength of Jupiter and Earth? How are the magnetic fields of Jupiter and Earth produced, respectively?

A

Jupiter: 5 x 10^-4 T
Earth 5 x 10^-5 T
Jupiter: hydrogen is so greatly compressed by J’s gravity that at its center hydrogen behaves like metal - conducting electricity.
Earth: liquid magma moving around Earth’s solid core generates electrical currents.

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30
Q

What is the principle of (Galilean?) relativity?

A

Physical laws are the same in any inertial frame.

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31
Q

Why did Maxwell’s prediction for a unique/specific value of c violate Galilean relativity?

A

Because Galilean relativity predicts that the speed of c will vary by frame of reference.

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32
Q

Einstein made a simple postulation to restore the prediction for a unique value of c. What was that postulation?

A

That c is constant regardless of frame of reference. c isn’t relative.

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33
Q

Why can only a charge that is accelerating generate an electromagnetic wave?

A

Electromagnetic waves are light. A charge must lose energy to accelerate.

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34
Q

Why did the null result obtained my Michelson and Morley disprove the need of an aether to explain light propagation?

A

The two beams returned at the same time; the beams remained in phase (no interference); thus, no aether wind.

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35
Q

Assuming there really had been an aether, how would it have been detected by Michelson and Morley?

A

The beams would have returned out of phase.

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36
Q

What does inertial mean?

A

Inertial means not accelerating

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37
Q

Space-like events can’t affect each other, but order of events can change. Time-like events can affect each other.

A

x

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38
Q

What is the principle of inertia?

A

An object with no force on it experiences no acceleration.

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39
Q

Facets of Newtons universal law of gravitation?

A

Gravity applies equally to celestial and Earth bound objects.
The moon is in free fall, just like Newton’s apple.
There is no difference between free fall and orbital motion except for the value of the “horizontal” speed.

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40
Q

Empedocles believed what about light?

A

Light is emitted from an inner fire generated within the eye that reflects off external objects back to the eyes

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41
Q

Lucretius believed what about light?

A

An “atomist”. Believed all things were composed of small particles; including light, which he believed emanated from the sun.

42
Q

What did Robert Hooke believe about motion and light?

A

All motion can be understood at a fundamental level as being periodic (repeating itself), light included, thus a wave.

43
Q

Newton believed different colors of light corresponded to particles of different mass.

A

x

44
Q

What are the 3 empirical rules of geometric optics?

A

1) Light in a uniform medium travels in a straight line.
2) Law of reflection: the angle of the incidence equals the angle of reflection.
3) Law of refraction: when entering glass or water from air (a different medium), light bends (refracts) toward the normal => angle of transmission is less than the angle of incidence.

45
Q

What are the characteristics of a (periodic) wave?

A

Wavelength (lamda): the distance between successive wave peaks.
Frequency (f): the number of wave peaks that pass a fixed point in 1 second.

46
Q

What is a transverse wave?

A

The oscillations are perpendicular to the direction of propagation of the wave

47
Q

What is a longitudinal wave?

A

The oscillations are parallel to the direction of propagation

48
Q

Range of frequencies nominally audible to humans is?

A

20 < f < 20,000 Hz

49
Q

The wavelengths of sound in air vary between?

A

20 m > lamda > 2 cm

50
Q

Ultrasound exists at how many Hz?

A

20,000 Hz or more

51
Q

What are wavelets?

A

Huygens view that waves propagate through wavelets. These are all of the points on a wave front. Something about tangent.

52
Q

What was Galileo’s lantern experiment?

A

1st documented attempt to measure the speed of light. One lantern opened in response to a first lantern opening. Measure time it takes for light to be seen by first lantern holder. It failed because c&raquo_space; human reaction time.

53
Q

Who first successfully measured the speed of light?

A

Ole Romer in 1676. The measurement was based on the eclipses of Jupiter’s MOON Io. He correctly deduced that the 3 min time discrepancy in Io’s orbit was due to the time it takes light to reach Earth.

54
Q

Time and space are not only flexible, they stretch.

A

x

55
Q

1 nanosecond (ns) is equal to?

A

10^-9 seconds

56
Q

Einstein’s 3 1905 papers introduced what?

A

1) the photon
2) evidence for atoms
3) special relativity

57
Q

Frame of reference: define

A

A spatial coordinate system that is motionless as seen from the perspective of a specific observer, along with a clock to keep track of time.

58
Q

3 features of a frame of reference?

A

1) a system of 3 orthogonal rulers to measure distance in x, y, z
2) we think of the observer and the clock to be AT REST in his/her reference frame
3) if two observers are in relative motion with respect to each other, they are in DIFFERENT reference frames

59
Q

Inertial reference frame: define

A

A frame that is not accelerating. A frame in which the principle of inertia is valid.

60
Q

Definition of event (ball example)?

A

An EVENT has a definite time and location. The trajectory of a thrown ball consists of separate events for each point of the trajectory (point x, y, z, at time t). The trajectory is a series of events.

61
Q

What is the Standard Configuration for TWO reference frames?

A

Motion is dealt with in only one dimension: motion along the x axis. Two reference frames S and S’ have coordinates (x, y, z, t) and (x’, y’, z’, t’). The clocks of S and S’ are synced (t = t’ = 0) when the origin of each frame aligns (x = x’ = 0)

62
Q

Special Relativity deals with inertial frames [inert] only; not accelerating frames.

A

x

63
Q

What is the relativity of simultaneity?

A

The ordering of events can depend upon frame of reference. We can reverse the order of events, depending of relative motion. Time is not absolute: it is relative.

64
Q

What are causally connected events as related to c?

A

As viewed from an arbitrary frame:
D is the distance between two events in the frame
T is the time interval between the two events in the frame
D/T is the speed a signal would need to travel from event 1 to event 2 in order to arrive before event 2 occurs, and vice versa.
Therefore, for one event to cause another, we need D/T < or = to c

65
Q

Space-like and time-like: relation to distance, time, and speed of light?

A

If two events are not causally connected in one frame, the are not causally connected in ANY frame.
“Time-like”: two events are causally connected if
D/T < or = to c
“Space-like”: two events are not causally connected if
D/T > c
Only events with space-like separation can have time order reversed by moving to a different reference frame

66
Q

Time dilation?

A

A consequence of special relativity. A moving clock runs slow.

67
Q

What is the gamma factor for different speeds?

A

gamma > 1 for all speeds not-equal 0
Thus, change in t > change in t’ for all speeds not-equal 0
As V –> 0, gamma –> 1
For low speed, gamma ~ 1 and change t ~ change t’
As v –> c, gamma –> infinity and time stands still in frame S’ as viewed from frame S.

68
Q

What dimension is introduced in the Lorentz transformations?

A

Converting from Galilean relativity to Einstein’s relativity introduces time as a coordinate - the “4th dimension”.

69
Q

What is length contraction?

A

A consequence of special relativity. A space interval (two points) must be measured simultaneously, but because simultaneity is relative, different observers will determine different lengths. An object is longest in its REST frame. Length contraction occurs only along the direction of motion. Space, like time, is relative.

70
Q

What is the Twin Paradox?

A

A consequence of special relativity. The brother who travels near c is younger than the Earth-bound brother because [there is more than one inertial frame for the c brother? Because there is one inertial frame on trip there, and another on the trip back?]

71
Q

Cosmic rays: particles and decay chain?

A

CR’s are very high energy protons from distant galaxies. The collide with molecules in the upper atmosphere at ~ 2 Km. These collisions create PIONS, which quickly decay to MUONS and NEUTRINOS.

72
Q

Lifetime/Distance traveled of a muon in its rest frame?

A

Lifetime = 2.2 x 10^-6 seconds. Because of time dilation, the average distance traveled 3.2 Km > 2 Km

73
Q

Noise canceling headphones: interference?

A

These use destructive interference to limit outside noise. A receiver detects the sound wave before they hit the ear, then a second out of phase wave is produced.

74
Q

Which particles do muons decay to?

A

Muons decay to one electron and two neutrinos

75
Q

The 2-slit interference experiment: explain

A

Thomas Young. Propagate light through a single slit; it then proceeds to two slits; the pattern then displays on a final surface (screen). Result: the predicted interference was seen - sometimes constructive and sometimes destructive interference (ie, the two beams interfered with one another), depending on how far each wave needs to travel to the screen.

76
Q

What is a KEY TOOL in astronomy that allows us to measure wavelengths of light, detect gravitational waves, etc. ?

A

Light interference, as demonstrated in the 2-slit experiment.

77
Q

What is the Poisson Spot?

A

A light is propagated toward an object. The light waves DEFRACT around the edges of the object (wavelets); constructive interference produces a bright spot in the center of the final screen. This was a deciding factor in establishing wave theory (and Foucault’s speed measurement), invalidating Newton’s particle theory[][][]

78
Q

Which colors are produced by longer and shorter wavelengths?

A 
Long = red
Short = blue
79
Q

Features of a super blood wolf moon?

A

super: moon is unusually close thus unusually big
blood: because it is red
wolf: 1st full moon in January is the “wolf moon” (in colonial America, wolves started their winter howling in January)

80
Q

Static electricity: define

A

A negative charge and a positive charge

81
Q

Greeks and static electricity: origins

A

Rubbing amber against fur creates static electricity. This is first mentioned by Thales of Miletus (“1st scientist; everything made from water”). The Greek word of amber is “elecktron”

82
Q

Early observations of magnetism: poles

A

permanent magnets exert forces “spontaneously”. Poles are North (N) and South (S). NN and SS repel. NS attract. This is different from static electricity.

83
Q

We define the direction of the magnetic field to be the direction that a compass needle points. It orients itself along the direction of the field lines of Earth.

A

x

84
Q

The use of magnetized materials as a directional tool (compass needle) was understood very early by the Chinese, Arabic, and Greek cultures. Place a magnetized needle-like iron mineral on a pivot.

A

x

85
Q

The electrostatic force law (Coulomb’s Law)?

A

Similar to Newton’s law of universal gravitation, with electric charge taking the place of mass. Unlike gravity, the force can be either attractive or repulsive.
F12 = F21 = k(q1q2/r^2)

86
Q

How was electromagnetism discovered?

A

Accidentally discovered when an electric current was activated near a compass. An electric current (moving electrical charge) creates a magnetic field - electricity and magnetism both arise from electric charge (current). This unified two major physical concepts and became known as electromagnetism.

87
Q

GPS steps, pt 1

A

1) GPS satellites send a radio signal giving their location and a “time stamp” t1 of when the signal was sent. 2) The GPS receiver (eg, a phone) compares t1 to the time the signal was received t2 to determine the distance to the satellite: D = c(t2-t1). 3) The position of the GPS receiver is thereby determined to be somewhere on a circle of radius D around the satellite.

88
Q

GPS steps, pt 2

A

4) the position is triangulated with corresponding information from other satellites to determine the receiver’s position. NOTE: this requires at least 4 satellite to be in view to determine the 3D location, AND it requires very accurate clocks w/ corrections for time dilation.

89
Q

GPS distance errors without time dilation

A

The satellites travel at speeds ~14,000 Km/hr
This yields a gamma factor of [][][]
The time dilation over the course of a day is 24 hours =
So, satellite clocks run slow by 7 [][][]
Without corrections for time dilation, the error in the distance would be ~ 2 Km per day: “an unacceptable lack of precision”

90
Q

Waves refract TOWARD the NORMAL (“toward the medium smaller wave speed” this is the water wave example). Also, “Deep water: fast. Shallow water: slow.”

A

x

91
Q

What does natural magnetism arise from?

A

Natural magnetism arises from aligned loops of current. The current is from electrons circularly orbiting around atoms. Very few elements (iron, bismouth, nickel) exhibit this natural alignment of VAST numbers of electron orbits in adjacent atoms, lead to magnetism.

92
Q

What would happen if Earth had no magnetic field?

A

Charged particles from the sun (the solar wind) would fry the planet; it would strip away the atmosphere, as it did to Mars after Mars lost its magnetic field; without the atmosphere, the oceans would evaporate and escape into space.

93
Q

Formation of auroras?

A

Trapped solar wind particles interact with air molecules in the upper atmosphere, exciting electrons to higher energy levels, which emit photons (gamma) when they return to their ground (lowest energy) states. O2 makes the color of auroras (on Earth) predominately green.

94
Q

James Maxwell unified and COMPLETED the laws of “classical electromagnetism”. These laws include ______
There are known as Maxwell’s equations.

A

The electric force law of Coulomb; analogous force law of magnetism; fact that magnetic poles can’t be isolated. Additionally, principle explaining electric generator: a changing magnetic field creates an electric field, and the reverse (changing electric creates magnetic). These predict a WAVE: an electromagnetic disturbance that propagates through space.

95
Q

The nature of electromagnetic waves ______

A

The electric (E) and magnetic (B) fields oscillate up and down in tandem, “in phase”. They oscillate perpendicular to each other and in the direction of propagation of the wave: a transverse wave. E and B are ALWAYS CHANGING - never constant.

96
Q

How are electromagnetic waves created?

A

Only accelerating electric charges can create electromagnetic waves. Any charge that accelerates will ALWAYS generate such a wave. Once a wave is generated, the wave is self-perpetuating and can travel forever.

97
Q

Electromagnetism “take-home message”

A

1) Electric charge generates an electric field
2) Moving electric charge generates a magnetic field
3) Accelerating electric charge generates electromagnetic radiation, which is light.

98
Q

Types of electromagnetic radiation ______

A

Radio waves, microwaves, infrared light, visible light, ultraviolet light, x-rays, gamma rays.

99
Q

Refraction vs. Diffraction?

A

Refraction: change of direction in waves that move from one medium to another.
Diffraction: bending of waves around objects.

100
Q

Facts given about Andromeda?

A

The Andromeda galaxy is 2.5 million light years away. If we could travel there at c-ish, we could make the round trip in 20 years; the Earth would be 5 million years older when we returned. Even at the speed of protons in the LHC (which travel at c-ish), that trip would take 800 years.

Physics 7 (2 decks)

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