Module 5 Flashcards
Define thermal contact
When energy is being exchanged between two objects due to a temperature difference
Define thermal equilibrium
A situation in which two objects would not exchange energy if they were placed in thermal contact
Define the zeroth law of thermodynamics
If object A and B are separately in thermal equilibrium with a third object C, then A and B are in thermal equilibrium with each other.
Define the first law of thermodynamics
Energy is always conserved
Define the second law of thermodynamics
Entropy of any isolated system always increases
Define the third law of thermodynamics
Entropy of a system approaches a constant value as the temperature approaches 0K
Define temperature
The property that determines whether an object is in thermal equilibrium with other objects
Describe how to calibrate the thermometer
Record where the liquid expands to at the freezing point of water, and the boiling point, and create a scale between the two marks
Describe how a constant-volume gas thermometer works
The level of mercury in column A can be set to fixed reference level by raising or lowering mercury reservoir, keeping a constant volume of gas The height of the mercury column indicates the pressure of the gas, and hence the temperature
Define heat
The amount of energy stored in a substance and can be regarded as the sum of the random kinetic and potential energies of all the molecules in that substance, so is dependent of temperature and the amount of substance present.
Describe the spacing, ordering and motion of atoms/molecules in a solid
Made up of particles arranged in a regular 3D structure, with strong forces of attraction between the particles, which can vibrate.
Describe the spacing, ordering and motion of atoms/molecules in a liquid
The particles are free to move around, so flows easily and has no fixed shape, but there are still forces of attraction between the particles.
Describe the spacing, ordering and motion of atoms/molecules in a gas
The particles are far apart and have virtually no forces of attraction and moe at high speed. Because they are further apart, they occupy a much larger volume than a liquid.
Describe the Brownian model
Elastic collisions between different molecules, allowing them move, giving strong proof for the kinetic model
Describe how the Brownian model can be observed
Air molecules will constantly strike smoke particles, so can be observed by watching smoke molecules under a microscope with light shining on it, and, as they have the same kinetic energy, they will move.
Define absolute zero
The lowest limit for temperature, at which a substance has minimum internal energy.
Describe the change in the internal energy of a body as its temperature rises
Whilst changing phase, increases due to increase in potential energy. When temperature increases, increases due to increase in kinetic energy.
Define specific heat capacity
The amount of energy required to raise one kilogram of a substance by one kelvin.
Describe an experiment to work out the specific heat capacity of a solid
Heat an insulated object, and time how long you are heating the object for, and the average current and voltage. E=IVt, and use E=MC∆T
Describe an experiment to work out the specific heat capacity of a liquid
Heat the liquid in a calorimeter and measure the change in temperature against time, with
Define specific latent heat of vaporisation
The amount of energy required to change one kilogram of a substance from a liquid to a gas
Define the specific latent heat of fusion
The amount of energy required to change one kilogram of solid into a liquid
Describe an experiment to work out the specific latent heat of vaporisation of a substance
An electric heater heats up the liquid in a flask, where the gas is then collected and condensed using a condenser and kept separate, so the mass can be measured.
Describe the assumptions when modelling a gas using the idea gas law
Large number of molecules in random, rapid motion Particles (atoms or molecules) occupy negligible volume compared to the volume of gas All collisions are perfectly elastic and the time of the collisions is negligible compared to the time between collisions Negligible forces between particles except during collision
Using the kinetic model, describe how gases cause pressure
The aroma or molecules are always moving, and when they collide with walls of a container, the container exerts a force on them, changing their momentum. A single atom with u ms^-1 will have a change in momentum of -2mu. The atom or molecule makes frequent collisions with the walls. Newton’s second law an be used to work out the force of the wall on the atom, and the third law states that this force will then have the same magnitude as the force exerted on the wall by the gas. As a large number of atoms or molecules will randomly collide with the wall, with a force F, and p = F/A, the pressure can be calculated.
State and describe Boyle’s Law
Pressure*Volume = Constant, so Pressure is indirectly proportional to Volume
Describe an experiment to prove Boyle’s Law
A gas in a sealed tube has the pressure slowly reduced, and its volume increase can be measured, as long as the gas inside the tube remains fixed.
Describe an experiment to work out an approximation for absolute zero
Place a sealed container of dry gas in a water bath, and measure the temperature. Measure the pressure of gas in the sealed container for different temperatures and plot a graph of Temperature against Pressure, and extrapolate the line to where it crosses the X-axis
Describe the equation of state of an ideal gas
pV=nRT, Where: p=Pressure, in kPa/Pa V=Volume, in dm^3/m^3 n=Number of Moles, in mol R=Gas Constant (8.31 mol J^-1 kg^-1) T=Temperature, in K
Define Root Mean Speed
The square root of all the mean square speeds of a gas particle
Describe the general distribution of the Maxwell-Boltzmann distribution
The distribution is an unsymmetrical bell shape, starting at the Origen, and tending towards zero as the speed of the particles increase. As the temperature increases, the distribution becomes more shifted, but the area under the graph remains the same.
Define the Boltzmann constant
k=R/N_a
Describe the internal energy of an ideal gas
Internal energy is the sum of kinetic and potential energy. One assumption of an ideal gas is that the electrostatic forces between particles in the gas are negligible, except during collisions, meaning there is no electrical potential energy in an ideal gas, so all the internal energy is in the form of the kinetic energy of the particle, so are directly proportional.
Give two reasons why the time which can be calculated to heat an object is often an underestimate
Some of the energy will be transferred to heat the surroundings; As the two objects approach thermal equilibrium, the temperature gradient decreases, so the rate of transfer of energy decreases.
Describe the change in internal energy when a mass of water of 100˚C becomes an equal mass of water vapour at 100˚C
Potential energy increases and kinetic energy stays the same, work is done to move the molecules apart.
Define the radian
The angle subtended by a cirular arc with a length equal to the radius of ther circle
Define the period of an object in circular motion
The amount of time it takes the object in circular motion to complete one full revolution
Define the frequency of an object in circular motion
The number of revolutions per second an object in circular motion has.
Define angular velocity
The rate of change of angle for an object moving in a circular path
Describe what causes an object to travel in a circular path
A constant net force perpendicular to the velocity of an object causes it to travel in a circular path
Define centripetal force
A force that keeps a body moving with a constant speed in a ciruclar path
Define centripetal acceleration
The acceleration of any object travelling in a circular path at constant speed, which always acts towards the centre of the circle
Describe an experiment using a whirling bung to investigate circular motion
A bung is swung in a horizontal circle through a glass or plastic tube, with a weight attached at the bottom. A paper clip is attached to help give a reference for a constant radius to the circle. The force the weight provides is equal to the centripetal force, and changing the angular velocity will change whether the centrapetal force is equal to the force the bung is exerting to leave the system
Explain how banked services work to allow objects to travel faster in a circle.
As well as friction contributing to the centripetal force, the horizontal component of the normal contact force will as well, so this will allow the centripetal force to increase, so a higher speed is achieveable
Describe the displacement of an oscillating particle
The distance between the equilibrium position and the particle
Define the amplitude of an oscillating object
The maximum dispacement from the equilibrium position
Define the period of an oscillating object
The time taken to compete one full oscillations
Define the frequency of an oscillating object
The number of complete oscillations per unit time
Define angular frequency
A quantity used in oscillator motion, which is equal to the product of the frequency of 2π
Define Simple Harmonic Motion
An oscillating motion for with the acceleration of the ofect is given by the negative angular frequency * diplacement, where the angular frequency is constant
Describe the shape of an acceleration against displacement graph for any object moving in SHM
The gradient is a proportional to the negative angular frequency squared, so is a straight negative line through the origin
Describe what an isochrounous oscillator is
An oscillator where the period of oscillation is costant, and is independent of the amplitude
Describe the interchange between kinetic and potential energy during simple harmonic motion.
The total energy in the system remains constant, assuming no friction, where the potential energy is at its maximum during maximum displacement, and zero at minimum displacement. As the only other type of energy with no friction is kinetic energy, it follows the inverse pattern
Describe the shape of an energy against displacement graph for an object in simple harmonic motion.
For the potential energy, you get a positive shaped parabola with a double root at zero;
For kinetic energy, you get a negative shaped parabola with its roots at the amplitude
The total of both energies is always equal to the total energy, which is constant
Describe the effect of light damping of a SHM system
The amplitude of the oscillations gradually decreases, but the period remains constant
Describe the effects of heavy damping for a SHM system
The amplitude decreases significantly, and the period of oscilation increases slightly
Describe the effects of very heavy damping on a SHM system
The oscillator would slowly move towards its equilibrium position, and not oscilated
Define free oscillation
The motion of a mechanical system displaced from its equilibrium position and then allowed to oscillate without anyh external forces
Define forced oscillation
An oscillation which a periodic driveer force is applied to an oscillator
Define natural frequency
The frequency of a free oscillation
Define resonance
The increase in amplitude of a forced oscillation when the driving frequency matches the natural frequency of the oscillating system
Describe the formation of a star
- Interstellar dust and gas forms over millions of years by gravitational attraction between particles
- The gravitational collapse of the cloud accelerates and denser regions form
- The GPE is transfered into thermal energy, forming a protostar.
- In order to become a star, nuclear fusion of hydrogen into helium has to occur.
- The star remains in a stable equilibrium when the gravitational force acting to collapse the star is balanced by the radiation from the photons emmited and the gas pressure from the nuclei in the core pushing out
Explain why a white dwarf will not collapse completely
Because the electron degeneracy pushing outwards is in equilibrium with the gravitational attraction of the entitities
Define a solar mass
The mass of something compared to the mass of the sun
Define the Chandrasekhar limit
The point at which the electron degeneracy pressure is overtaken by the gravitational attraction of the entities
Describe the axis on a Hertzsburg-Russel (HR) diagram
Luminosity against temperature, but temperature is reversed
Describe the shape of the main sequence star on an HR diagram
A region in a relatively straight line between bright and hot cool and dark
Describe the shape of a Red Supergiant on a HR Diagram
A region of high luminosity across a range of temperatures
Describe the shape of a Red Giant on a HR diagram
A region of high luminosity across a middle to low temperature
Describe the evolution of a low-mass star from its main sequence
- The radiation and gas pressure drops as fusion reduces, causing the core to collapse, but fusion continues in a shell around the core which expands and cools, becoming a red giant.
- The outer layer then drifts off, leaving its core which is a white dwarf
- The outer layer which drifts off then forms a planetary nebula
Describe the evolution of a massive star
- As the star is much hotter, the fusion of helium happens and continues until iron is formed, where fusion cannot happen any further, giving an iron core.
- The layers of fusion inside the star implode and bounce of the solid core, leading to a shockwave that ejects all material into space, forming a supernova.
- The rement core is then compressed
- If less than three solar masses (and above the Chandrasekar limit), the gravitational collapse continues to form a neutron star, with similar density of an atomic nucleus
- If greater than three solar masses, it compresses the core resulting in a gravitational field so strong that not even photons can escape.
Define Wein’s Displacement law
That the maximum intesity wavelength is inversely proportional to its surface temperature
What is one Astronomical Unit (AU)
The average distance between the earth and the Sun
Define a light year
The distance travelled by light in one year in a vacuum
Define the parsec
An object at a distance of 1 parsec subtends an angle of 1 arc second when measured against a fixed background.
How many degrees are in 1 arcsecond?
1/3600 of a degree
Define the cosmological principle
The universe is both isotropic and homogeneous
Define isotropic in terms of the cosmological principle
On a large scale the universe is uniform, so the same in all directions
Define homogenous in terms of the cosmological principle
It has a uniform density
Give experimental evidence for the Big Bang, and how this can prove the cosmological principle
That the universe has background radiation at an average temperature of around 2.7K, and as this is consistent across the whole galaxy, it is uniform across all directions.
Define Planet
An object which is in orbit around a star with three characteristics:
- Large enough mass for it’s gravity to give it a round shape
- No fusion reactions
- Cleared its orbit of most other objects
Define planetary satellites
A body in orbit around a planet
Define comets
Small irregular bodies made up of ice, dust and small pieces of rock.
Define galaxy
A collection of stars and interstellar dust and gas
Define solar system
A planetary system consisting of a star and at least one planet orbiting around it.
Define universe
Everything which exsists within space and time
Define energy levels of electrons
A discrete quantised amount of energy that an electron within an atom is permitted to possess
Describe what happens when an electron moves from a lower energy level to a higher energy level
External energy is added and the atom which the electrons are in are said to be excited
State four facts about the energy levels of electrons
- An electron cannot have a quantity of energy between two levels
- The energy levels are negative because external energy is required to remove an electron from the atom, so the negative value also idicate that the electrons are trapped within the atom or bound to the positive nuclei
- The energy level with the most negative value is known as the ground level/state
- An electron with zero energy is free from the atom
Describe what happens when an electron moves from a higher energy level to a lower energy level
The electron loses energy and a photon is emitted from the atom, and this is known as de-excitation
Suggest why different atoms having different spectral lines is useful
For this can be used to indentify elements within stars
Describe emission line spectra
Each element produces a unique emission line spectrum because of its unique set of energy levels
Describe Continous spectra
All visible frequencies or wavelengths are present. The atoms of a heated solid metal will produce this type of spectrum
Describe absorbtion line spectra
This type of spectrum has series of dark spectral lines against the background of a continous spectrum. The dark lines have exactly the same wavelenghts as the bright emission spectral lines for the same gas atoms
Describe how an emission line spectra can occur
If the atoms in a gas are excited, then when the electrons drop back into lower energy levels, they emit photons with a set of discrete frequencies specific to that element.
Describe how an absorption line spectra can occur
Light from a source that produces a continuous spectrum passes through a cooler gas. As the photons pass through the gas, some are absorbed by the gas atoms, raising electrons up into higher energy levels and so exciting the atoms. Only photons with energy exactly equal to the difference between the different energy levels are absorbed, meaning that only specific wavelenghts are absorbed, creating dark lines in the spectrum.
Describe why on an absorption line spectra the dark lines are due to the photons which have been absorbed
- Photons of the same energy as the difference between energy levels are absorbed, making the atom excited
- Photons of the same frequency are then re-admitted
- As the re-admitted photon travels in all directions, the intensity of the photon is massively reduced
Describe how different elements within starts can be detected
- Continous light spectra is produced from the star
- Outer layers of cooler gas absorb some the photons
- The absorbtion line spectrum is compared to known elements and can be used to determine which elements are present
Define diffraction grating
An optical component with reguarly spaced slits or lines that diffract and split light into beams of different colours travelling in different directions
Describe what happens to light when passed through a diffraction grating.
- Light is split into a series of narrow beams
- The direction of these beams depends on the spacing of the lines or slits or the grating and the wavelength of the light.
- When white light passes through, it splits into its component colours, making gratings especially useful in spectroscopy
Define the Doppler effect
The change in frequency and wavelength of waves received from an object moving relative to an observer compared with what would be observed without relative motion.
Define Hubble’s Law
The recessional velocity of a galaxy is directly proportional to its distance from the earth
What is the approximation for the age of the universe?
1/H0 (Inverse Hubble’s Law)
Describe the evolution of the universe from the Big Bang to the present
- Time and space is created and the Universe exists as a singularity
- Universe expands readily (inflation). No matter exists; only high energy gamma-ray photons
- Universe cools enough to form first fundamental particles through pair production
- Quarks combine to form first hadrons
- Hadrons combine to form deuterium and helium nuclei along with small amounts of other elements. Expansion is so rapid that no heavier elements form than Beryllium
- Universe is cool enough to form the first atoms, and nuclei capture electrons. The EM radiation from this stage is detected as CMBR
- First stars appear and heavier elements are formed through fusion in the stars
- Milky Way is formed
- Solar system is formed from the nebula left by the supernova of a larger star
- The average temeperature of the universe is currently 2.7K
Name the three things the universe is made up from?
Dark energy, Dark Matter and matter
Define gravitational field strength
The gravitational force exerted per unit mass on a small object placed at that point within the field
What causes there to be a gravitational field
Any object with a mass creates a gravitational field around them
Describe what are gravitational field lines and how they are used
Straight lines going towards the centre of an object, and shows the direction and strenght of the field
Describe what causes a uniform gravitational field.
If the field lines are parallel and equidistant.
Describe the gravitatinal field strength of the earth
It is uniform close to the surface of the earth and numerically equal to the acceleration of free fall
Define Kepler’s first law of Planetary motion
The orbit of a planet is an ellipse with the sun at one of the two foci points
Explain why Earth’s orbit is modelled as a circle
For Kepler’s first law of planetary motion states the all orbits are elliptical, but the difference if the two foci points in Earth’s oribt is so small, that it can be modelled as a circle
Define Kepler’s Second law of planetary motion
A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time
Define Keplerls Third law of planetary motion
The square of the orbital period (T) of a planet is directly proportional to the cube of its average distance (r) from the sun
Derive the equation:
T2 = ((4π2)/GM)*r3
See Picture
Give the three conditions for a satellite to be in geostationary orbit
- Be in orbit aboce the Earth’s equator
- Rotate in the same direction as the Earth’s rotation
- Have an orbital period of 24 hours
State the use of geostationary satellites
As they are always in the same place above the earth, they can be used for communication, as they always know where to send the signal to.
Define gravitational potential
The work done per unit mass to move an object to that point from infinity
What is gravitational potential energy?
The work done to move the mass from infinity to a point in a gravitational field, so E=mVg.
Define escape velocity
The minimum velocity for an oject to lift itself out of the gravitational field
Suggest why some planets are able to have an atmosphere, whilst others aren’t
- In order to escape the planet’s gravitational field, the gas molecules need a large enough escape velocity
- As the average kinetic energy of a single gas atom or molecuel is given by 1/2mc2 where c is the rms speed of the molecules. At any given temperature, some molecules will be travelling faster than this r.m.s speed, and those molecules can escape
- This is dependent on the temperature and the surface gravitational field strength of the planet
