Physics - Recall for Chapter 19; Stars
Flashcards
2022-04-14
What is the universe?
Everything that exists.
What is a protostar?
A hot dense sphere of gas prior to the ignition of nuclear fusion in the core that creates a star.
What provides the energy required for a protostar to begin fusion?
Gravitational potential energy is transferred to thermal energy.
What is nuclear fusion?
The fusing of light nuclei to produce heavier nuclei releasing energy in the process.
What is required for nuclear fusion to occur?
Extremely high temperatures and pressures.
What prevents gravity from causing stars to collapse?
The radiation and gas pressure pushing outward.
Why do large stars tend to remain stable for less time than smaller stars?
The pressure and temperature in the core is higher so they fuse hydrogen more quickly.
What is radiation pressure in a star?
Pressure from the photons created by fusion in the core of a star.
What is the gas pressure in a star?
Pressure of the nuclei in the star’s core pushing outwards.
What is a main sequence star?
A stable star fusing hydrogen into helium.
What causes a star to leave the main sequence?
It runs low on hydrogen, affecting the stability of the star.
What is a red giant?
A bright, cool star in the stage after the main sequence for a star with insufficient mass to go supernova.
Why is a red giant bright?
Because it has a large surface area.
What is the structure of a red giant?
An inert core surrounded by shells fusing elements heavier than hydrogen.
What is a white dwarf?
The very hot, dense remnant core of a red giant star. No fusion happening.
What happens for red giants with masses below the Chandasekhar limit?
The stars form white dwarfs.
What happens for red giants with masses above the Chandrasekhar limit?
The stars form neutron stars or black holes.
What is the numerical value of the Chandrasekahr limit?
$1.4$ solar masses.
What is electron degeneracy pressure?
A quantum mechanical effect (due to the Pauli exclusion principle) which prevents the collapse of a stellar core to create a neutron star in white dwarves.
What is the final element produced in a red giant?
Carbon.
What is the final element produced in a red supergiant?
Iron.
What is a red supergiant?
A huge star in the last stages of its life prior to undergoing a supernova explosion.
What elements are produced in a supernova?
All elements, including those heavier than iron.
What is a (Type II) supernova?
The process of collapse of a red supergiant (at the end of its life) into a neutron star or black hole and the associated ejection of large amounts of stellar material into space.
What is a neutron star?
The extremely dense remnant core of a red supergiant star made almost entirely of neutrons.
What is a planetary nebula?
The outer layers of a red giant star driven off in the shockwave produced by the final collapse of the star.
What is a black hole?
The end stage of a stellar core with sufficient mass and density for its escape velocity to exceed the speed of light.
What is a Hertzsprung-Russell Diagram?
A log-log plot of luminosity (on the y-axis) against average surface temperature (backwards on the x-axis) for a group of stars.
What is the luminosity of a star?
The energy radiated per second by the star.
What is a black body?
A perfect emitter and absorber of radiation.
What is a black body spectrum?
The characteristic spectrum of radiation emitted by all black bodies in thermal equilibrium with their surroundings.
What is Wien’s displacement law in words?
The peak emission wavelength of a black body spectrum is inversely proportional to the body’s absolute temperature.
What is Stefan’s Law in words?
The total power emitted per unit surface area by a black body is proportional to the 4th power of the absolute temperature.
What does it mean that electron energy levels are “discrete”?
Electrons cannot exist between energy levels.
What is a continous spectrum?
A continuous set of EM radiation of all frequencies.
What is an emission spectrum?
A dark background with individual bright lines corresponding to specific frequency photons from specific energy level transitions by electrons in the atom.
What is an absorbption spectrum?
A continuous spectrum with dark lines representing photons absorbed by specific energy level transfers by electrons in the atom.
What happens in excitation of an atom?
The atom gains energy and an electron moves up to a higher energy level.
What are two processes that can lead to the excitation of an atom?
A collision with a charged particle or the absorption of a photon by an electron in the atom.
What occurs during de-excitation of an atom?
An excited electron drops down energy levels and emits a photon.
What determines the frequencies that photons can be absorbed or emitted by an atom?
The size of a gaps between energy levels in the atom.
What determines if a photon can be absorbed or emitted by an atom?
The energy of the photon must be equal to a gap between energy levels.
What is $d$ in
\[n \lambda =d \sin \theta\]
?
Distance between slits in a diffraction grating
What is $n$ in
\[n \lambda =d \sin \theta\]
?
Order of the maximum
What name is given to the central maximum formed by a diffraction grating?
The zero-order maxium.
What is the path length difference between adjacent slits along the nth order maximum?
$n$ wavelengths.
How do you find the highest order maximum for a diffraction grating?
$\frac{d}{\lambda}$ rounded down to the nearest whole number.
How do you calculate the number of maxima produced by a diffraction grating?
where $n$ is the highest order of a maximum.
What is the effect of reducing the spacing of slits in a diffraction grating?
It increases the angles of each maximum.
What is the effect of increasing the wavelength incident on a diffraction grating?
It increases the angles of each maximum.