Random Shit Flashcards
Describe absorption spectrums
Dark lines against a background of continuous spectrum corresponding to wavelengths that’s have be absorbed
Why do you get circular diffraction patterns?
The graphite atoms are not lined up in the same direction
Why is the understanding of the universe unreliable
- There is no experimental evidence
- Laws of physics unknown
- Energy/temperature unreproducible
What’s the importance of gravity in fusion
- pulls together nucleons
- ∴ increases p
- ∴ increases Hz of collisions
- temp
- allows fusion (close enough blah blah)
Evolution of the universe after BB
- v.dense + v.hot singularity
- All forces = United
- U expanded + cooled
- During inflation: U = sea of quarks, leptons, photons + antiquarks
- More matter than antimatter
- U cools enough for quarks -> protons, hadrons, neutrons
- Protons cool -> He nuclei
- e- + He and H -> atoms form
- Temp = 2.7K
- Gravity -> formations of stars + galaxies
How has exerts P
- when p collide w/wall = Δp
- F exerted by P = N’s 2nd law
- N’s 3rd law
- Pressure = ΣF/A of wall
How can v of galaxies be determined
Doppler shift of spectral lines
Suggest why measurements for our nearest galaxies can deviate from current Hubble trend line
Gravitation attraction between nearby galaxies affects motion
Suggest why measurements for galaxies at larger distances can deviate from current Hubble trend line
Expansion rate not constant
Possibly due to dark energy?
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
- 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.
Suggest why the activity of a sample undergoing carbon-dating is measured over a long time period and then averaged
• The activity is very small, so a long time is needed to build up enough data.
Explain why the method of carbon-dating is not appropriate for samples that are greater than 105 years old
• The activity of a very old sample is so low that it cannot be differentiated from the background.
Explain why nuclei with less than approximately 56 nucleons cannot produce energy by fission
• The binding energy per nucleon will decrease for fission, which is impossible unless external energy is supplied.
Describe briefly the sequence of events which occur in the formation of a star
- 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.
Define the impulse of a force
Force x time for which the forces acts
Describe advantages of using a datalogger
- 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
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
- 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
Moment
Turning effect of a force around a turning point
What are 3 things that affect fluid friction?
- 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
Describe 3 things about friction
- always act in opposite motion to object
- can never speed something up/start something moving
- converts eK -> heat
Terminal velocity
When Drag (frictional forces) = weight (driving force)
Work done
F x distance moved in direction of the F
Brownian motion
Zigzag, random motion of small particles suspended in a fluid
What is potential E
E that is stored + caused by interactions between particles
Describe the Kelvin scale
- Independent on property of a substance (eg. B.p or m.p)
* particles E dp T
As temp increases, what happens to the maxwell Boltzmann distribution
- avg. particle speed increases
- max particle speed increases
- distribution curve becomes more spread out
Why does the avg speed of particles remain the same (provided T is constant)?
- 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
How are f and T related to A
Independent of amplitude
Describe difference in amplitude-frequency graphs of lightly damped and heavily damped systems
- 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
Gravitational field
Force field generated by any object w/mass which causes another object w/ mass to experience an attractive F
Gravitation field strength
F per unit mass
How does spectrum allow you to identify elements
Different atoms = different E levels ∴ unique emission spec
Explanation of dark matter
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
Dark energy
- due to gravity, surely expansion of universe should be slowing down
- astronomers found that expansion is speeding up - possibly due to dark energy
How are supernovas formed
- 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
Neutron stars
- if neutron come is intact + 1.4-3solar masses
- v.dense ∴ small
- composed of n
Pulsars
• Neutron stars that rotate rapidly + emit directional bursts of EM waves
Black holes
- if remains of core is collapsed + > 3solar masses
- v.dense + a infinitely dense singularity
- v.strong g
- boundary at which v=c = even horizon
Parsec
A star is 1 parsec away if angel of parallax is 1arc second
How is a protostar formed
Gravity = pulls matter/interstellar dust + gas -> WD on dust and gas particles -> increase in eK -> increase T until hot enough to glow
Why can protostars only be detected through infrared telescopes?
Clouds of dust + gas around them (nebulae) absorb + scatter most visible light
What’s the overall effect of the fusion of H
4 protons -> He-4 nuclei w/ production of 2 gamma photons, 2 neutrinos + 2 positrons
What inaccuracies are there in Hubble’s law
Difficult to determine distance ∵ relative motion may no be along line of sight between source + observer
How did Hubble measure velocities of galaxies
Red shift calculations
Newton’s 2nd law
Force on an object = rate change of p
TAKES PLACE IN DIRECTION OF THAT FORCE
List + describe energy changes in mass-spring system
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
Describe effect of small increase in T to atoms in solid
Greater amplitude if vibrations
Principle of momentum
Total p before = total p after
PROVIDED NO EXTERNAL FORCES
Supporting BIG BANG
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
Describe white dwarf
V.hot, low lum, v.dense, v.small remnant of a low mass star
No fusion occurs
Why is a star brightest at lowest temp
Eg. Red giant
Large surface area
Suggest why it’s difficult to predict the future of the universe
Existence of dark matter and dark energy and Hubble constant is not known accurately
What does Hubble’s law apply to
Receding galaxies
Does not apply to stars in our own galaxy
Suggest nature and origin of dark matter
H/He has
Formed after BB
Describe carbon dating
- 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
Describe geostationary satellites
- always above same point on earth
- equatorial orbit
- same T as earth (24hrs)
- same angular speed
- same direction of rotation
Barton’s pendulums
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
How is a red giant formed
- 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
Describe how a LDR, a voltmeter, a variable resistor and a cell can act as a PD divider circuit
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
Explain why certain objects don’t have their W acting in the middle of it
Distribution of mass isn’t uniform
Describe how wearing a seatbelt/having an airbag can help protect the driver
- increase time to stop
- ∴ decreases F on driver
- wide area of airbag = reduces pressure
- deflates quickly to prevent whiplash
