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Physics A Level > Random Shit > Flashcards

Random Shit Flashcards

1
Q

Describe absorption spectrums

A

Dark lines against a background of continuous spectrum corresponding to wavelengths that’s have be absorbed

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2
Q

Why do you get circular diffraction patterns?

A

The graphite atoms are not lined up in the same direction

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3
Q

Why is the understanding of the universe unreliable

A
  1. There is no experimental evidence
  2. Laws of physics unknown
  3. Energy/temperature unreproducible
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4
Q

What’s the importance of gravity in fusion

A
  • pulls together nucleons
  • ∴ increases p
  • ∴ increases Hz of collisions
    • temp
  • allows fusion (close enough blah blah)
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5
Q

Evolution of the universe after BB

A
  1. v.dense + v.hot singularity
  2. All forces = United
  3. U expanded + cooled
  4. During inflation: U = sea of quarks, leptons, photons + antiquarks
  5. More matter than antimatter
  6. U cools enough for quarks -> protons, hadrons, neutrons
  7. Protons cool -> He nuclei
  8. e- + He and H -> atoms form
  9. Temp = 2.7K
  10. Gravity -> formations of stars + galaxies
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6
Q

How has exerts P

A
  • when p collide w/wall = Δp
  • F exerted by P = N’s 2nd law
  • N’s 3rd law
  • Pressure = ΣF/A of wall
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7
Q

How can v of galaxies be determined

A

Doppler shift of spectral lines

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8
Q

Suggest why measurements for our nearest galaxies can deviate from current Hubble trend line

A

Gravitation attraction between nearby galaxies affects motion

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9
Q

Suggest why measurements for galaxies at larger distances can deviate from current Hubble trend line

A

Expansion rate not constant

Possibly due to dark energy?

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10
Q

Explain why during the closest approach of an alpha particles (during alpha scattering off a gold nucleus) the gold nucleus has a velocity and the alpha particle does not

A
  • There is a repulsive electrical force between the gold nucleus and the alpha particles;
  • linear momentum is conserved because there are no external forces;
  • The initial kinetic energy of the alpha particle is transformed into electrical potential energy.
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11
Q

Suggest why the activity of a sample undergoing carbon-dating is measured over a long time period and then averaged

A

• The activity is very small, so a long time is needed to build up enough data.

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12
Q

Explain why the method of carbon-dating is not appropriate for samples that are greater than 105 years old

A

• The activity of a very old sample is so low that it cannot be differentiated from the background.

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13
Q

Explain why nuclei with less than approximately 56 nucleons cannot produce energy by fission

A

• The binding energy per nucleon will decrease for fission, which is impossible unless external energy is supplied.

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14
Q

Describe briefly the sequence of events which occur in the formation of a star

A
  • Interstellar dust and gas clouds are drawn together by gravitational forces;
  • The loss in gravitational potential energy increases the temperature of the gas;
  • Fusion of protons occurs;
  • Energy is released from the fusion reactions, where protons fuse together into helium;
  • A stable star is formed when the gravitational pressure is equal to the radiation pressure.
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15
Q

Define the impulse of a force

A

Force x time for which the forces acts

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16
Q

Describe advantages of using a datalogger

A
  • can provide continuous record of data (over long periods of time)
  • can record very short timescale signals (at intervals)
  • can start and stop recording automatically
  • data can be fed directly to computer for analysis
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17
Q

Explain why the terminal p.d. of a car battery is less than the e.m.f. when the car starter motor is turned on

A
  • the battery has internal resistance
  • when the starter motor is turned on the total resistance in the circuit decreases
  • the current flowing increases
  • the voltage drop across the internal resistance of the battery increases
  • V = E - Ir
  • terminal p.d. = emf – p.d. across internal resistance
  • the terminal p.d. of the battery decreases
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18
Q

Moment

A

Turning effect of a force around a turning point

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19
Q

What are 3 things that affect fluid friction?

A
  • F depends on viscosity of fluid
  • F increases as speed increases
  • F depends on size + shape of object moving through it. Greater area = greater F
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20
Q

Describe 3 things about friction

A
  • always act in opposite motion to object
  • can never speed something up/start something moving
  • converts eK -> heat
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21
Q

Terminal velocity

A

When Drag (frictional forces) = weight (driving force)

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22
Q

Work done

A

F x distance moved in direction of the F

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23
Q

Brownian motion

A

Zigzag, random motion of small particles suspended in a fluid

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24
Q

What is potential E

A

E that is stored + caused by interactions between particles

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25
Q

Describe the Kelvin scale

A
  • Independent on property of a substance (eg. B.p or m.p)

* particles E dp T

26
Q

As temp increases, what happens to the maxwell Boltzmann distribution

A
  • avg. particle speed increases
  • max particle speed increases
  • distribution curve becomes more spread out
27
Q

Why does the avg speed of particles remain the same (provided T is constant)?

A
  • E is transferred between particles
  • some gain, some lose
  • ∴ although E of individual P changes at each collisions, it doesn’t alter total E of system
28
Q

How are f and T related to A

A

Independent of amplitude

29
Q

Describe difference in amplitude-frequency graphs of lightly damped and heavily damped systems

A
  • LD = v.sharp resonance peak
  • A only increases dramatically when DF = close to NF
  • HD = flatter response
  • A increases little when DF = NF
  • resonance occurs @ slyly lower DF than NF
30
Q

Gravitational field

A

Force field generated by any object w/mass which causes another object w/ mass to experience an attractive F

31
Q

Gravitation field strength

A

F per unit mass

32
Q

How does spectrum allow you to identify elements

A

Different atoms = different E levels ∴ unique emission spec

33
Q

Explanation of dark matter

A

1) MACHOs (Massive Compact Halo Objects) - objects of normal matter that’s so dense = gives off no light
2) WIMPs (Weakly Interactive Massive Particles) - particles that don’t interact w/ EM force but do w/ gravity
3) dark matter doesn’t exist

34
Q

Dark energy

A
  • due to gravity, surely expansion of universe should be slowing down
  • astronomers found that expansion is speeding up - possibly due to dark energy
35
Q

How are supernovas formed

A
  • Gravitational pressure -> forces p + e in Fe to combine into n
  • triggers blowing out of outer shell
  • heavier elements other than iron can be formed
36
Q

Neutron stars

A
  • if neutron come is intact + 1.4-3solar masses
  • v.dense ∴ small
  • composed of n
37
Q

Pulsars

A

• Neutron stars that rotate rapidly + emit directional bursts of EM waves

38
Q

Black holes

A
  • if remains of core is collapsed + > 3solar masses
  • v.dense + a infinitely dense singularity
  • v.strong g
  • boundary at which v=c = even horizon
39
Q

Parsec

A

A star is 1 parsec away if angel of parallax is 1arc second

40
Q

How is a protostar formed

A

Gravity = pulls matter/interstellar dust + gas -> WD on dust and gas particles -> increase in eK -> increase T until hot enough to glow

41
Q

Why can protostars only be detected through infrared telescopes?

A

Clouds of dust + gas around them (nebulae) absorb + scatter most visible light

42
Q

What’s the overall effect of the fusion of H

A

4 protons -> He-4 nuclei w/ production of 2 gamma photons, 2 neutrinos + 2 positrons

43
Q

What inaccuracies are there in Hubble’s law

A

Difficult to determine distance ∵ relative motion may no be along line of sight between source + observer

44
Q

How did Hubble measure velocities of galaxies

A

Red shift calculations

45
Q

Newton’s 2nd law

A

Force on an object = rate change of p

TAKES PLACE IN DIRECTION OF THAT FORCE

46
Q

List + describe energy changes in mass-spring system

A

KE: 0 at lowest + highest points. Increases to max at equilibrium

GPE: increases as mass goes from lowest to highest

EP: decreases as mass goes from lowest to highest

47
Q

Describe effect of small increase in T to atoms in solid

A

Greater amplitude if vibrations

48
Q

Principle of momentum

A

Total p before = total p after

PROVIDED NO EXTERNAL FORCES

49
Q

Supporting BIG BANG

A

1) spectra from galaxies show shift to longer wavelengths = moving away
2) distance galaxies are moving faster
3) CMBR points
3) existence of primordial helium

50
Q

Describe white dwarf

A

V.hot, low lum, v.dense, v.small remnant of a low mass star

No fusion occurs

51
Q

Why is a star brightest at lowest temp

A

Eg. Red giant

Large surface area

52
Q

Suggest why it’s difficult to predict the future of the universe

A

Existence of dark matter and dark energy and Hubble constant is not known accurately

53
Q

What does Hubble’s law apply to

A

Receding galaxies

Does not apply to stars in our own galaxy

54
Q

Suggest nature and origin of dark matter

A

H/He has

Formed after BB

55
Q

Describe carbon dating

A
  • living creatures take in C-14
  • C-14:C-12 is determined for the sample
  • “ “ “ “ “ “ is determined currently
  • age is found using x= x0 e^wavelength * t
  • limitation = C-14: C-12 assumed to be constant
56
Q

Describe geostationary satellites

A
  • always above same point on earth
  • equatorial orbit
  • same T as earth (24hrs)
  • same angular speed
  • same direction of rotation
57
Q

Barton’s pendulums

A

1) E is transmitted along the thread -> pendulums undergo forced oscillation
2) pendulum … responds more than others ∵ same length as X
3) ∴ = same T as X + same natural Hz ∴ resonates w/X
4) phase difference is π/2
5) response of other pendulums depends on how close their lengths are to X

58
Q

How is a red giant formed

A
  • when H fuel has run out + fused into He fusions stops ∴ radiation pressure stops
  • inward movement due to force of g
  • core contracts -> increases T
  • H outer layer expands and cools -> red giant
59
Q

Describe how a LDR, a voltmeter, a variable resistor and a cell can act as a PD divider circuit

A

1) Resistor + LDR connected in series
2) V meter placed in parallel across either resistor
3) state eqt (V1/V2 =…)
4) resistance of LDR decreases as intensity of light increases
5) describe of V meter changes

60
Q

Explain why certain objects don’t have their W acting in the middle of it

A

Distribution of mass isn’t uniform

61
Q

Describe how wearing a seatbelt/having an airbag can help protect the driver

A
  • increase time to stop
  • ∴ decreases F on driver
  • wide area of airbag = reduces pressure
  • deflates quickly to prevent whiplash

Physics A Level (14 decks)

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