Karteikarten
Physics Unit 5
Karten in diesem Stapel (71)
- 1conditions necessary for nuclear fusionHigh temperatures are required so that average velocity becomes high enough so that they can overcome the electrostatic repulsion force between two positively charged nuclei
‐so that they come close enough and join together to reach a nuclear diameter
‐Very high density is required so that there is enough collision rate to sustain a fusion reaction - 2Internal energy isThe sum of the kinetic energy of individual particles + all of the potential energy of the individual particles
- 3What happens at phase changes?All energy put in is used to break bonds, temperature stays constant
- 4What is the Maxwell Boltzmann distribution?The Maxwell-Boltzmann equation, which forms the basis of the kinetic theory of gases, defines the distribution of speeds for a gas at a certain temperature. From this distribution function, the most probable speed, the average speed, and the root-mean-square speed can be derived
- 5What is the relationship between pressure and volume (Boyle's law)P α 1/V
- 6What is the relationship between pressure and temperature (pressure law)P α T
- 7Assumptions of an ideal gas (5)1. No intermolecular forces are acting between the molecules
potential energy = 0
Thus phase changes are not possible
2. Particles collide perfectly elastically with each other and the container walls
3. The particles act as 0 point masses, they have 0 size
4. Particles are identical
5. Enough particles are present so that statistics can be applied - 8Binding energythe energy that holds a nucleus together, equal to the mass defect of the nucleus.
- 9Definition of simple harmonic motionAcceleration/Force is proportional to displacement from equilibrium position, and always acts towards the equilibrium position
- 10Types of DampingUnder damping: the particle takes a long time and many oscillations to return to its original position
critical damping: When displaced it returns to equilibrium position the quickest/shortest time without over shooting
Over damping: The system returns to equilibrium without oscillating
- 11Definition of resonanceIf a system is forced to vibrate at its natural frequency it will absorb increasing amounts of energy and increase in amplitude (to its maximum). Energy transfer is maximum
- 12Intensity wavelength diagramAs temperature increases the most intense wavelength decreases
As temperature increases intensity for all wavelengths increases - 13Hertzsprung Russel DiagramStars located near the top end of the main sequence have higher masses
- 14spectroscopic parralaxMeasure spectra emitted using radiation spectrometer and find λ max
Use Wien's law to find temperature
Use Hertzsprung Russel diagram to find luminosity
Measure radiant energy flux using radiation Intensity meter
Use L and F to find d - 15Cepheid variable starsStars that vary in luminosity due to changes in the size of the star caused by expansions and contractions
A graph of luminosity to the log of the period of variation in days produces a linear relationship - 16Determination of distance of a Cepheid variable starTime period variable star is observed and the average value of T is determined. Higher the time period,higher the intrinsic luminosity of the star.This luminosity is noted from the recorded value.It's average radiation flux,F is noted measured the radiation intensity meter.By using the equation F=L/4πd^2,we can determine the distance of the variable star.
- 17How does increasing the heat to a container increase pressure(Average) kinetic energy of molecules/atoms is greater
Collision rate of molecules with balloon increases
Rate of change of momentum is greater
Therefore a greater force on the container walls - 18State what is meant by dampingDamping is a resistive force that acts in the opposite to the velocity of the oscillation.
Idea that damping is the transfer of energy away from the oscillating system as work is done against resistive force
it reduces amplitude of vibration
So that oscillations die away quickly - 19what is an arc second1/3600 of a degree
- 20ParsecIt's the distance a star must be from the Sun in order for the angle Earth-Star-Sun to be 1 arc second
- 210 degrees Kelvin-273
- 22Gravitational field strength linking acceleration, mass and radiusg=GM/r²
- 23fusion VS fission(Hydrogen) fuel for fusion is very abundant,
Fission relies upon (uranium) a relatively limited resource
Fusion results in few radioactive products
(Radioactive) products produced in fission present significant disposal problems
For a given mass of fuel, the energy released by fusion is greater than the energy released by fission
Fusion requires high density and temperature which leads to confinement problems. Strong magnetic fields are required to contain the plasma. If plasma touches the walls of the reactor its temperature falls (and fusion
stops)
There is little possibility of a runaway fusion (unlike for fission) - 24Describe nuclear fusion, how it releases energy, why only light mass elements can be used1. small mass nuclei come very close together to form a more massive nucleus
2. Mass of fused nucleus is less than sum of masses of fusing nuclei
Mass difference releases energy according to ∆E = c²∆m
3. For energy to be released the binding energy (per nucleon) must increase. The binding energy per nucleon only increases for light nuclei - 25Similarities and differences between electro-static force and gravitational forceBoth:
are radial fields
extend of an infinite range
are inversely proportional to the distance squared
Gravitational field can be shielded
electrostatic forces can be repulsive and attractive
The force between (unit) charges at a given separation is much stronger than the force between (unit) masses at the same separation
Electric fields can cancel or reinforce but gravitational fields always reinforce one another - 26What is a property of a plastically deforming materialit absorbs large amounts of energy
- 27Relationship between the density of the universe and the future of the universeIf the density of the universe is less than the critical density then the universe will keep expanding (Open Universe)
If the density of the universe is equal to the critical density then the universe will keep expanding but at an ever decreasing rate to a constant size (Flat Universe)
If the density of the universe is more than the critical density then the universe will decelerate its expansion and collapse back in on itself and eventually ending in a Big Crunch(Closed Universe) - 28What does spontaneous meanSpontaneous means that the decay cannot be
influenced by any external factors. - 29What does random meanRandom means that we cannot identify which atom/nucleus will (be the next to) decay
- 30Describe the current stauts of the sun and its futureThe Sun is fusing hydrogen
When (hydrogen) fusion ceases the core of the Sun cools [accept radiation pressure drops when fusion/burning ceases in the core]
The core collapses (under gravitational forces)
The core becomes hot enough for helium fusion to begin (in the core)
The Sun expands and becomes a red giant
Helium begins to run out and the core collapses again (under gravitational forces)
Idea that outer layers of Sun are ejected into space
The temperature doesn't rise enough for further fusion to begin
The core/Sun becomes a (white) dwarf star - 31Outline how parallax measurements are used to determine the distance to nearby starsThe star is viewed from opposite ends of the earth's diameter at 6 month intervals.
The change in angular position of the star against backdrop of fixed stars is measured.
The diameter of the Earth's orbit about the Sun must be known and trigonometry is used to calculate the distance - 32Explain how the use of a standard candle enables the distance to more distant objects to be determined.Flux/intensity of standard candle is measured.
Luminosity of standard candle is known.
Inverse square law is used.
Distance too far for Trigonometric parralax to be used - 33Why is positron emission unlikely in a Neutron rich atomsBecause it increases the number of neutrons
- 34A car is set into vertical oscillation by applying a momentary downwards force. Show that the frequency of oscillation f is given by f= 1/2π √k/mFor spring F=kx
Resultant force kx acts on car where x is displacement from equilibrium
ma=-kx
a= -ω²x
ω²=k/m
use of ω=2πf
f= 1/2π √k/m - 35As the gas cloud contracts the internal energy of the system increases. Explain how energy conservation applies to the system during this period of contraction.Gravitational potential energy decreases (as cloud collapses)
Decrease in (gravitational) potential energy equals increase in internal energy - 36Explain how the fusion of hydrogen into helium in the core enables large amounts of energy to be released.Mass is converted to energy according to ∆E=c²∆m where Δm is the mass deficit/lost
Although energy released per fusion is small, fusion rate is very large - 37Recent measurements indicate that Polaris may be significantly closer to the Earth than previously thought. Explain why this would have a significant impact on our estimation of the age of the universe.If Polaris were closer,
Its known luminosity would be less than previously calculated
The distances to other astronomical bodies would be less than previously calculated
So the Hubble constant would be greater than previously calculated
As age = 1/H₀ the universe would not be as old as previously calculated - 38Explain why an alpha particle (He4) is more likely than any other small nucleus to be emitted from a large unstable nucleus.The B.E. per nucleon for 4 He is greater than other small nuclei
Hence the energy released by the nucleus is greatest for alpha decay - 39Recent measurements indicate that Polaris may be significantly closer to the Earth than previously thought. Explain why this would have a significant impact on our estimation of the age of the universe.If Polaris were closer,
Its known luminosity would be less than previously calculated
The distances to other astronomical bodies would be less than previously calculated
So the Hubble constant would be greater than previously calculated
As age = 1/H₀ the universe would not be as old as previously calculated - 40Explain why an alpha particle (He4) is more likely than any other small nucleus to be emitted from a large unstable nucleus.The B.E. per nucleon for 4 He is greater than other small nuclei
Hence the energy released by the nucleus is greatest for alpha decay - 41Describe how Hubble was able to determine the velocities of the nebulae and explain how his conclusion provides evidence for an expanding universe.Doppler shift formula used to calculate velocities
Nebulae/galaxies were moving away from the Earth
The further away the galaxy the faster it was moving
Therefore all galaxies are moving away from each other - 42What is activityThe rate of decay of unstable nuclei
- 43Shielding is placed around the core of the reactor. State one physical property this shielding must have and name the material that is usually used.Must have high density
Concrete - 44It is difficult for scientists to estimate the average density of the universe reliably. Explain why.The mass of the universe is uncertain because of the amount of dark matter is uncertain
Since dark matter doesn't interact via the electromagnetic interaction
The value of the Hubble constant is uncertain
Since measurements of distances to distant galaxies are uncertain - 45Explain how redshift can be used to determine the velocity of a galaxy relative to the EarthMeasure wavelength of light emitted from galaxy
Compare wavelength to the wavelength for a source on the Earth
States appropriate Doppler formula - 46Explain how Hubble's law can be used to find a value for the age of the universeSee v = H₀d and v = d/t
Therefore t = 1/ H₀ - 47Suggest how this microwave "noise" which can be observed in space may show evidence for an expanding universe.Originates from the Big Bang
Microwave radiation comes from the universe itself Or it is cosmic background radiation [accept CMB]
Microwave wavelength linked to temperature of universe [e.g. indicates a temperature of space of about 3 K]
Originally the universe was a hotter place than it is now Or temperature decreases as the universe expands
Wavelength has been increased Or frequency decreased. - 48What ares the stellar classification and the temperatures associatedO (25-50KK) Blue
B (10-25KK) Blue white
A (7.5-10KK)White
F(6-7.5KK)White-yellow
G(4.5-6KK)Yellow
K(3.5-4.5KK)Orange
M(2-3.5KK)Red - 49How to find distance to far far away galaxiesMeasure spectra emitted using radiation spectrometer and find λ of blue light
Determine the difference between this wavelength and the same blue light's wavelength in a lab source.The wavelength of the lab source is the actual λ and the light from the distant galaxy is the observed λ.
The Doppler equation is used to determine the velocity of the galaxy
Hubble's law is used to determine the distance - 502 stars were created at the same time, one is now a white dwarf, why must the white dward be more massive when createdSirius B has already evolved from a main sequence star
So Sirius B had a shorter main sequence lifetime
Sirius B must have had a larger rate of fusion
Hence there was a higher temperature and a greater density within Sirius B
This implies much greater gravitational forces within the star - 51Use the idea of binding energy per nucleon to explain why the fission of nuclei with large numbers of nucleons releases large amounts of energy.‐Nuclear fission is the splitting of a large nucleus into smaller nuclei
‐The mass of the (fission) fragments is less than the mass of the original nucleus
‐E = mc2, the binding energy per nucleon is greater in the fragments than in the original nucleus - 52What is meant by Half Life?The average time taken for the activity of a sample to halve.
- 53Massive stars can only produce elements up to iron (Fe) in their cores by fusion. Using the Binding Energy graph against nucleon number graph, Explain why?‐Idea that 56Fe is the peak of the graph
‐If nuclei were to be formed with A > 56, the B.E./nucleon would decrease
‐This would require a net input of energy and so does not occur - 54Why most energy in a decay is transferred to alpha particles?‐Momentum is conserved
‐Initial momentum is zero
‐nuclei travel on opposite so momentum is zero
‐Although the alpha has a smaller mass it has a bigger velocity/speed
‐And velocity/speed is squared in the energy expression - 55Why all geostationary satellites are in orbit above earths equator?‐The satellite must rotate with the Earth
‐The satellite must be in a geosynchronous orbit
-There must be common axis of rotation between the satellite and the earth - 56Why the internal energy of an ideal gas can be taken as a total kinetic energy of the molecules?‐Internal energy is the sum of kinetic energy and potential energy
‐Molecules in an ideal gas have zero potential energy - 57Using principle of conservation of energy, explain why the amplitude of an oscillation will decrease to zero?‐Although total energy remains constant
‐Energy is dissipated
‐As work is done against frictional forces - 58the total energy of an undamped simple harmonic oscillator is...always constant
- 59forced oscillationforced oscillation
- 60How does damping reduce the amplitude of a SHM oscillator?resistive forces reduce the total energy of the system; the displacement of the oscillator on each cycle gets smaller and smaller; therefore reduces the amplitude eventually to zero
- 61Stefan-Boltzmann LawStefan-Boltzmann Law
- 62Radiation Flux is...L/(4πd^2),(Power/Area),intensity
It also determines the brightness of the luminous object.Hence Radiation Flux ∝ Brightness - 63Doppler red shiftapparent shift in spectrum to the red end due to the movement of the light emitting object in space away from the observer, z =∆λ/λ ≈ ∆f/f ≈ v/c
- 64nuclear fissionA nuclear reaction in which a massive nucleus splits into smaller nuclei with the simultaneous release of energy
- 65nuclear fusiona nuclear reaction in which atomic nuclei of low atomic number fuse to form a heavier nucleus with the release of energy.
- 66Why do nuclei with large nucleon number, like uranium 235, release large amounts of energy on the BE per nucleon graph?- in fission, the nucleus splits to form less massive fragments.
- these fragments are higher up the BE per nucleon Curve.
- The increase in BE is very small, but the large no. of nucleons means that the overall energy realized is very large. - 67Describe an experiment using absorbents of different material that could be carried out to identify the sources. You must explain how the data collected could be used to distinguish between the three sources.- With no source present, record the background count.
- Handling the source with tongs, fix one source close to the GM-tube.
- Introduce a sheet of paper/aluminium between the source and the GM-tube.
- If paper/aluminium reduces the count rate to background levels it is the americium source.
-If paper causes no change in the count rate it is the strontium source.
- If paper reduces the count rate but the count rate is still above background
levels it is the radium source - 68What is meant by activity of a radioactive source?It is the rate of decay of an unstable nuclei
- 69Why does/doesn't the radiation pose a health risk?Alpha radiation:
- The Range is only a few cm in the air
- Cannot penetrate the layer of dead skin cells
Beta radiation:
- It is moderately ionising
- beta radiation is able to penetrate the body
- once inside, it may mutate/damage DNA of cells
Gamma:
- gamma (and protons) not very ionising
Common:
- very short half life - 70Why the brightness of a Cepheid Variable Star keeps varying?Cepheid Variable star are stars that have left the main sequence.They still have some of their nuclear fuel(hence they still can undergo nuclear fusion).They alternately expand(when energy production increases) and contract(when energy production drops),causing their brightness to vary repeatedly.
- 71Doppler ShiftIt is the change in frequency of a wave for an observer moving relative to its source.
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