# Physics - Recall for Chapter 19: Stars > Source: https://ollybritton.com/notes/a-level/physics/recall-questions/chapter-19-stars/ · Updated: 2022-04-14 · Tags: physics, school, a-level, 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?? $$2n+1$$ 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. --- Olly Britton — https://ollybritton.com. Machine-readable index: https://ollybritton.com/llms.txt