The sun and other stars Flashcards Preview

Physics (Elliott) > The sun and other stars > Flashcards

Flashcards in The sun and other stars Deck (62):
1

What does studying the radiation emitted by stars, such as the Sun, helps us to understand?

Studying the radiation emitted by stars, such as the Sun, helps us to understand the processes that occur when stars are formed, create new elements and eventually die. There are several types of star, depending on their age and mass. And there is some convincing evidence of ‘extrasolar’ planets that orbit hundreds of nearby stars, other than the Sun.

2

How do Electrons move between energy levels?

Electrons orbit in fixed energy levels around the nucleus inside an atom. They can move between these energy levels when they absorb energy (by moving to higher energy levels) or when they release energy (by moving to lower energy levels

3

are several energy level transitions possible within one type of atom ?

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.

4

an element absorbs and emits energy at a range of............... .....................

an element absorbs and emits energy at a range of characteristic frequencies.

5

It is common to measure temperature on what scale?

It is common to measure temperature on the Celsius scale, with ice melting at 0oC and water boiling at 100oC.

6

Physicists often prefer to use a different scale - what is 0 K is defined as? .

Physicists often prefer to use the Kelvin scale - on which 0 K is defined as absolute zero.

7

What is absolute zero?

This is the coldest temperature possible. At absolute zero, all the particles in a substance stop moving. They have no energy left to lose, so the substance cannot get any colder.


8

An increase in temperature of ten degrees Celsius is the same as an increase of what Kelvin? Converting is easy, as long as you remember that absolute zero (0 K) is -?

An increase in temperature of ten degrees Celsius is the same as an increase of ten Kelvin. This makes converting between them quite easy, as long as you remember that absolute zero (0 K) is -273oC.

9


How do you convert from Kelvin to degrees Celsius?


To convert from degrees Celsius to Kelvin, add 273.

To convert from Kelvin to degrees Celsius, subtract 273.


.

10

How do you convert from degrees Celsius to Kelvin?

To convert from degrees Celsius to Kelvin, add 273

11

When a gas cools down what happens to the particles?

They lose energy.

.

12

As mass is fixed, does the velocity of the particles decrease or increase as gas cools down?

decreases.

13

If a gas of fixed mass and volume is cooled down, what will happen to its pressure? Why is this?

If a gas of fixed mass and volume is cooled down, its pressure will decrease steadily. This is because each particle takes longer to reach the walls of the container, and therefore will do so less frequently and with less momentum.

14

If a gas of fixed mass and pressure is cooled down,what happens to its volume? why is this?

If a gas of fixed mass and pressure is cooled down, its volume decreases steadily. This is to compensate for the decreased frequency of collisions that are also weaker.

15

As the pressure or volume of a gas decreases, what happens to the temperature ?

As the pressure or volume of a gas decreases, the temperature will approach absolute zero (the coldest temperature possible).

16

At what point will the particles have lost all of their energy ? (so there will be no collisions with the walls of the container and therefore no pressure)

Absolute zero has a value of -273oC (0 K). This is the point at which the particles will have lost all of their energy, so there will be no collisions with the walls of the container and therefore no pressure

17

The pressure of a gas is caused by the particles ............ with the sides of the container, exerting a .......... per unit of area. The .............. depends on the frequency of collisions and the force of the particles’ momentum

Pressure and volume

The pressure of a gas is caused by the particles colliding with the sides of the container, exerting a force per unit of area. The pressure depends on the frequency of collisions and the force of the particles’ momentum (the momentum is calculated by multiplying the mass of a particle by its velocity).

18

The momentum is calculated by ?

multiplying the mass of a particle by its velocity

19

The unit of pressure is what?

The unit of pressure is the pascal (Pa)

20

what is a pascal (Pa)?

pascal (Pa) - which is the same as the force of one newton spread over an area of 1 square metre.

21

If the volume of a container containing a gas is halved, what happens to the pressure? What must the temperature remain?

If the volume of a container containing a gas is halved, the pressure doubles. This relationship only works if the temperature remains constant

22

How can the gas law be summarised in an equations?

pressure x volume = constant
This relationship only works if the temperature remains constant

23

As the temperature increases, what happens to the particles ? What does this do to them?

As the temperature increases, the particles have more energy and move faster. This increases their momentum and makes them collide with the sides of the container with more force.

24

If the volume is kept constant, what is the effect of doubling the temperature?.

If the volume is kept constant, the effect of doubling the temperature will be to double the pressure.

25

If the container is allowed to expand at constant pressure, the effect will be what?

If the container is allowed to expand at constant pressure, the effect of doubling the temperature will be to double the volume

26

What happens to a gas when it is compressed?

Both these changes work in reverse. For example, a gas can actually be heated up by compressing it

27

Two gas laws can be represented using two equations. What are they?
(When using these equations, the temperature must be in measured in what?)

These two gas laws can be represented using the following equations:
pressure/temperature = constant
volume/temperature = constant
(When using these equations, the temperature must be in Kelvins.)



28

How is a protostar formed?

A star begins its life as a cloud of gas, which is mostly hydrogen and helium. The particles experience a very weak attraction towards each other due to gravity.

29

As the gas cloud becomes denser what happens next?

As the gas cloud becomes denser, the effect of gravity is to increase the pressure and temperature. As more gas is drawn in by the increasing gravity, the mass of the cloud increases and therefore so does its gravity.

30

The increasing gravity does what to form the protostar?

The increasing gravity compresses the gas further so that it becomes hotter and denser. It eventually becomes a protostar.

31

How does the star become a stable main sequence star.?

When the temperature and pressure become high enough, the hydrogen nuclei fuse into helium nuclei, releasing large amounts of energy. The star is now a stable main sequence star.

32

What happened in the 20th century to progress our understanding of nuclear fusion in stars?

In the early 20th century, research into nuclear processes provided scientists with a possible explanation for the Sun’s energy source

33

What is nuclear fusion?

In a star, hydrogen nuclei fuse (whereby two smaller nuclei join to make a larger one) and produce helium nuclei, releasing energy in the process. This is called nuclear fusion.

34

Atoms that are ............ than hydrogen can also fuse together in stars. Most of the fusion occurs in the ....... of a star, where the ...............and .....................is greatest.

Atoms that are heavier than hydrogen can also fuse together in stars. Most of the fusion occurs in the core of a star, where the temperature and density is greatest.

35

The more massive the star, the ........... its core, so it can create heavier elements by ............. .

The more massive the star, the hotter its core, so it can create heavier elements by fusion.


36

What is the most massive atom that can be created by fusion?

The most massive atom that can be created by fusion is iron

37

What is the equation for nuclear fusion?

i dont know - but its worth looking up

38

How do red giants come about?

In the core of the Sun, and all other main sequence stars, helium is formed from hydrogen nuclei that fuse together. When main sequence stars of a similar size to our Sun leave the main sequence, they become red giants.

39

What is the most massive atom that can be made in a red giant?

Oxygen is the most massive atom that can be made in a red giant - which has a mass that is three times greater than that of the Sun

40

What happens when an explosion creates a nuclei which are more massive than iron.

If the mass of the star is many times greater than the Sun, fusion can produce heavier nuclei, up to and including iron. When the core of a massive star is mostly iron, it explodes as a supernova. This explosion creates nuclei which are more massive than iron.

41

A star has a structure that in some ways is similar to what?

A star has a structure that in some ways is similar to the structure of our planet.

42

Which is the hottest and most dense part of the star? What takes place there and what is released?

The core is the hottest and most dense part of the star. This is where nuclear fusion takes place and where high energy photons are released.

43

Where does nuclear fusion take place and where are high energy photons are released?




This is where nuclear fusion takes place and where high energy photons are released


44

How is energy is transported to the surface of the star?

Energy is transported to the surface of the star by photons of radiated energy and also via powerful convection currents (the movement of molecules in fluids, in this case energy transferred in the plasma).

45

What is the photosphere?

is the outer part of the star, where the photons are radiated into space.

46

When does a star leaves the main sequence ? What happens and what does it become?




a star leaves the main sequence when it runs out of hydrogen to fuse. It swells and, depending on its mass, becomes a red giant or a red supergiant as its photosphere cools.

47

what is a supernova>

If the mass of the star is many times greater than the Sun, fusion can produce heavier nuclei, up to and including iron. When the core of a massive star is mostly iron, it explodes as a supernova. This explosion creates nuclei which are more massive than iron.

48

How are red giants formed?

In the core of the Sun, and all other main sequence stars, helium is formed from hydrogen nuclei that fuse together. When main sequence stars of a similar size to our Sun leave the main sequence, they become red giants.

49

What is the hottest and most dense part of the star. ?

the core is the hottest and most dense part of the star. This is where nuclear fusion takes place and where high energy photons are released.

50


In a red giant, the core is …………...and the ………….. is rising.


In a red giant, the core is contracting and the temperature is rising.

51

what happens in a red giant or red supergiant?

In a red giant or red supergiant, helium nuclei fuse to make carbon, followed by heavier elements such as nitrogen and oxygen.

52

How is a white dwarf formed?

A red giant (formed from stars like the Sun) lacks the mass to fuse nuclei to compress the core further, so after fusion has finished it cools to become a white dwarf. Because there is no more fusion taking place, the star cools and fades.

53

When a super nova is formed what does it leave behind?

It leaves behind a dense neutron star or a black hole.

54

What is a massive main sequence star?

it is a star several times the mass of the Sun

55

Fusion can produce elements with masses up to and including iron. When the core becomes mostly iron, it explodes into a …………... This creates elements with ………... greater than iron.

In a massive main sequence star (several times the mass of the Sun), fusion can produce elements with masses up to and including iron. When the core becomes mostly iron, it explodes into a supernova. This creates elements with masses greater than iron.

56

In a red giant, the core is ………...and the temperature is ………..

In a red giant, the core is contracting and the temperature is rising.

57

what is The Hertzsprung-Russell diagram ?

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.

58

what are extrasolar planets?




Astronomers have found convincing evidence of planets that orbit more than one hundred stars, other than the Sun. These planets are called extrasolar planets. Initially, giant gas planets were discovered, but recently astronomers have identified smaller rocky planets similar to Earth.

59

Why do scientists believe that life already exists elsewhere in the universe.

Even if a small proportion of stars have extrasolar planets orbiting them, many scientists believe that it is likely that life already exists elsewhere in the universe

60

It is estimated that there are around how many stars in our galaxy?

It is estimated that there are around 100 billion stars in our galaxy.

61

what equation did Einstein devise to work out the amount of energy that is released during nuclear fusion and fission

E = mc2 E = mc2
Energy produced (joules) = mass of matter lost (kg) x (speed of light in a vacuum)2 (m/s)

62

During chemical reactions, what happens to mass? What happens to mass in nuclear reactions?

During chemical reactions, mass is always conserved because atoms are not created or destroyed - only rearranged. However, in nuclear reactions such as fusion and fission, mass is converted into energy.