# GCSE Physics P7 (OCR) - Sun, and Stars

### Description

GCSE Physics (P7) Flashcards on GCSE Physics P7 (OCR) - Sun, and Stars, created by Josh Price on 26/04/2015.
Flashcards by Josh Price, updated more than 1 year ago
 Created by Josh Price over 8 years ago
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## Resource summary

 Question Answer What do all hot object do? Emit a continuous range of electromagnetic radiation, whose luminosity and peak frequency increase with temperature. What is ionisation? The removal of electrons from atoms. What do spectral lines provide evidence for? The chemical elements present within the object investigated. Why is the volume of a gas inversely proportional to its pressure, at room temperature? Each collision with a wall causes a tiny force, Together, billions of collisions produce gas pressure. If the same amount of gas is compressed into a smaller volume, then the collisions will be more frequent, and so the pressure will be greater. Why do the pressures and volumes of a gas vary with temperature? The colder the environment, the less energy the particles have. So, they strike the walls less frequently, and with less momentum. This decreases the pressure. If the pressure is to remain constant, the volume of the gas must decrease to compensate for the fact that the collisions are weaker and less frequent. What is absolute zero? -273 K How do you calculate constants of a gas? = Pressure x Volume = Pressure / Temperature = Volume / Temperature How does a protostar form? 1) A cloud of gas and dust is pulled together by gravity. It breaks up into several smaller clouds, and each continues to contract. 2) Within a contracting cloud, each particle attracts each other particle, so that the cloud collapses towards its centre. It forms a rotating, swirling disc. 3) As the particles are attracted towards the centre, they move faster, which means the gas gets hotter. 4) Eventually, the temperature of this material is hot enough for fusion to occur, and a star is born. What is nuclear fusion? The reaction of two hydrogen nuclei fusing together to form a helium nuclei because the strong nuclear force acts on them if they get so close together. How do you calculate the energy released during nuclear fusion? Energy = (Mass Lost x Speed of Light) ^2 The more _______ the star, the _________ its core and the __________ the nuclei created by fusion. Massive Hotter Heavier How is energy transported from core to surface in a star? By photons of radiation and by convection. 1) Radiation (photons) travels outwards through the radiative zone. 2) Convection currents arise in the convective zone, and they carry heat energy to the photosphere. 3) Electromagnetic radiation is emitted by the photosphere and radiates outwards through the solar atmosphere. What is the Hertzsprung-Russell diagram? A plot of temperature and luminosity. Where is each type of star located on the HR Diagram? White Dwarfs: Bottom Left Main Sequence: Across the middle Giants: Top Right Supergiants: Top, Top Right Where does fusion occur in a main sequence star? In its core. When does a star leave the main sequence? What happens to it? When its core hydrogen runs out. It swells to become a red giant or supergiant and its photosphere cools. What happens in a red giant or supergiant? Helium nuclei fuse to make carbon, followed by further reactions that produce heavier nuclei such as nirtrogen and oxygen. What happens to a low-mass star? It becomes a red giant, which lacks the mass to compress the core further at the end of helium fusion. It then shrinks o form a white dwarf. What doesn't happen in a white dwarf? Nuclear fusion. So the star gradually cools and fades. What happens in a high-mass star? Nuclear fusion can produce heavier nuclei, including iron. When the core is mostly iron, it explodes as a supernova creating nuclei with masses greater than iron and leaving a dense neutron star or a black hole. What are exoplanets? Planets which are orbiting other stars. What is the evidence for exoplanets? a) Small dips in the brightness of a star indicate a planet passing in front of it. b) The wobbling motion of a star is caused by the gravity of a planet.

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