P7 Quiz - Stars

All hot objects, including stars, emit a continuous range of radiation in the electromagnetic spectrum.

When atoms in a pure element are [blank_start]excited[blank_end] (given lots of energy) they give off light at fixed and [blank_start]characteristic[blank_end] frequencies. These frequencies directly relate to the colour - from low frequency [blank_start]infrared[blank_end], through the visible spectrum, and up to high frequency [blank_start]ultraviolet[blank_end]. These emission line spectra are like a chemical [blank_start]fingerprint[blank_end] for that element. They are caused by the movement of electrons between energy [blank_start]levels[blank_end] in the atoms. Hydrogen has the [blank_start]simplest[blank_end] emission spectrum. A [blank_start]star[blank_end] will give off energy at a range of [blank_start]frequencies[blank_end], but there will be some gaps in it. The gaps in the spectrum from the Sun correspond exactly to the lines in the emission [blank_start]spectrum[blank_end] for hydrogen. This means that there is hydrogen present in the Sun, which is [blank_start]absorbing[blank_end] light of specific frequencies.

There are several energy level transitions that are possible within one type of atom - so an element absorbs and emits energy at a range of characteristic frequencies.

Boyle's Law states that [blank_start]pressure[blank_end] is inversely proportional to volume. The pressure of a gas is caused by the [blank_start]particles[blank_end] colliding with the sides of the container, exerting a [blank_start]force[blank_end] per unit of area. The pressure depends on the [blank_start]frequency[blank_end] of collisions and the force of the particles’ momentum (which is [blank_start]constant[blank_end] as the gas is kept at a constant temperature). If the volume of the container [blank_start]halves[blank_end], there is half the amount of space for particles to move around in, making [blank_start]collisions[blank_end] more likely. As the number of collisions [blank_start]increases[blank_end], so does the pressure.

The Pressure Law states that...

What is absolute zero?

How many Kelvin would water boil at?

Charles' Law is defined as which of the following?

A star begins its life as a [blank_start]cloud[blank_end] of gas, which is mostly [blank_start]hydrogen[blank_end] and helium. The particles experience a very weak attraction towards each other due to [blank_start]gravity[blank_end]. As the gas cloud becomes [blank_start]denser[blank_end], the effect of gravity is to increase the [blank_start]pressure[blank_end] and temperature. As more gas is drawn in by the increasing gravity, the mass of the cloud [blank_start]increases[blank_end] and therefore so does its gravity. The increasing gravity [blank_start]compresses[blank_end] the gas further so that it becomes hotter and denser. It eventually becomes a [blank_start]proto[blank_end]star. When the temperature and pressure become high enough, the hydrogen nuclei [blank_start]fuse[blank_end] into helium nuclei, releasing large amounts of [blank_start]energy[blank_end]. The star is now a stable [blank_start]main sequence[blank_end] star.

Isotopes of an element have the same number of protons but a different number of neutrons.

Nuclear fusion: the process of two nuclei binding together to make a new [blank_start]element[blank_end] and releasing [blank_start]energy[blank_end]. Stage 1: Protium (Hydrogen-[blank_start]1[blank_end]) + Protium --> Deuterium (Hydrogen-[blank_start]2[blank_end]) + positron + ENERGY Stage 2: [blank_start]Protium[blank_end] + Deuterium --> Tritium (Hydrogen-[blank_start]3[blank_end]) + ENERGY Stage 3: Tritium + Tritium --> [blank_start]Helium[blank_end] + Protium + Protium + ENERGY OR Deuterium + Tritium --> Helium + neutron + ENERGY

Nuclear fusion can occur in the core of main sequence stars because the high temperatures and pressure are able to force nuclei close enough together to overcome the electrostatic repulsion. Nuclei bigger than helium have larger electrostatic repulsive forces, so can only fuse in the cores of larger, denser stars such as a red giant or red supergiant.

A star has a structure that in some ways is similar to the structure of our planet. The core is the [blank_start]hottest[blank_end] and most dense part of the star. This is where [blank_start]nuclear fusion[blank_end] takes place and where high energy [blank_start]photons[blank_end] are released. Energy is transported to the surface of the star by photons of [blank_start]radiated[blank_end] energy and also via powerful [blank_start]convection[blank_end] currents (the movement of molecules in fluids, in this case energy transferred in the plasma). The [blank_start]photosphere[blank_end] is the outer part of the star, where the photons are radiated into space.

The Hertzsprung-Russell diagram is a plot of temperature against luminosity. It identifies regions where supergiants, red giants, main sequence stars and white dwarfs are located.