Chapter 19 and 20 - Space

Question 1

How is a protostar formed?

Answer 1

In a nebula, gravitational forces pull together dust and gas. As regions in the nebula get denser, gravitational energy is converted into thermal energy. This region is known as a protostar.

Question 2

What needs to happen for a protostar to become a star?

Answer 2

Nuclear fusion needs to start in its core

Question 3

Which two forces push outwards to keep the shape of a main sequence star stable?

Answer 3

radiation pressure from photons emitted during nuclear fusion and gas pressure.

Question 4

What is a solar mass?

Answer 4

The mass of the Sun

Question 5

Stars with low mass have a…

Answer 5

cooler temperature

Question 6

How is a red giant formed?

Answer 6

The energy released from nuclear fusion inside a main sequence star is reduced to the point that it is now less then the force of gravity pulling the star together. The core of the star begins to collapse, as the core shrinks the pressure increases enough for fusion to start in a shell around the core. This causes the outside of the star to expand, as these layers expand they cool, as they cool they turn red.

Question 7

What will stars of mass between 0.5M and 10M evolve into?

Answer 7

Red giants

Question 8

What will stars of mass greater than 10M evolve into?

Answer 8

Red supergiants

Question 9

What is the heaviest element that will form inside the core of a red supergiant?

Answer 9

Iron

Question 10

What is electron degeneracy pressure?

Answer 10

Pressure created inside of a collapsing star due to the Pauli exclusion principle(Two electrons can not exist in the same energy state).

Question 11

What is the Chandrasekhar limit?

Answer 11

1.44M, The maximum Mass of a star that electron degeneracy pressure is sufficient to prevent gravitational collapse. This is the maximum stable mass of a white dwarf star.

Question 12

What are the two outcomes of a supernova?

Answer 12

Neutron star or a black hole

Question 13

What is the Hertzsprung-Russell diagram?

Answer 13

A graph of the stars in our galaxy that shows the relationship between their luminosity and their average surface temperature.

Question 14

What are energy levels?

Answer 14

Electrons bound to atoms in a gas can only exist in one of discrete set of energies, knows as energy levels.

Question 15

Why are energy levels negative?

Answer 15

Because external energy is required to remove the electron from the atom.

Question 16

An electron with zero energy is…

Answer 16

free from the atom

Question 17

The energy level with the most negative energy is known as the…

Answer 17

ground state

Question 18

State the three kinds of spectra

Answer 18

Emission line
Continuous
Absorption line

Question 19

Why does each element produce a unique emission line spectra?

Answer 19

Each element has a unique set of energy levels

Question 20

What is a continuous spectra and what will produce one?

Answer 20

All visible frequencies of light are produced. Produced by the atoms of a heated solid metal.

Question 21

How is an absorption line spectra produced?

Answer 21

When a continuous spectrum passes through a gas cooler than the source of the continuous spectrum. As the light passes through the gas some of the photons are absorbed by the gas, only photons with energy exactly the energy need to raise electrons to higher energy levels are absorbed, this creates dark lines in the spectrum.

Question 22

What is a black body?

Answer 22

An idealised object that absorbs all EM radiation that shines onto it and when in thermal equilibrium emits a characteristic distribution of wavelengths at a specific temperature.

Question 23

State Wien’s displacement law

Answer 23

The wavelength emitted with maximum intensity from a black body is inversely proportional to its temperature.

Question 24

State Stefan’s law

Answer 24

The luminosity of a star is directly proportional to:

its radius squared
its surface area
its surface absolute temperature ^ 4

Question 25

What is an astronomical unit?

Answer 25

1.5 x 10^11m The average distance between the Earth and the Sun.

Question 26

What is a light year?

Answer 26

9.46x10^15m The distance travelled by light in a vacuum in a year.

Question 27

What is a parsec?

Answer 27

3.1 x 10^16m The distance at which a radius of 1 Au subtends an angle of one arcsecond.

Question 28

What is Hubble’s law?

Answer 28

The recessional speed of a galaxy is almost directly proportional to the distance from the Earth.

Question 29

What is the cosmological principle?

Answer 29

The universe is homogeneous (Matter is distributed uniformly across the universe), isotropic (The universe looks the same in every direction to every observer) and the laws of physics can be applied across the universe

Question 30

What are the two key pieces of evidence that support the big bang theory?

Answer 30

Hubble’s law(The universe is still expanding)

microwave background radiation