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Edexcel ScienceiGCSE Physics
N. Stars and Fusion2019-2020
Name:________________Physics Teacher:______________
House CG
Specification Checklist
Year 10
8.07 understand how stars can be classified according to their colour
8.08 know that a star’s colour is related to its surface temperature
8.09 describe the evolution of stars of similar mass to the Sun through the following stages:
• nebula • star (main sequence)• red giant• white dwarf
8.10 describe the evolution of stars with a mass larger than the Sun
8.11 understand how the brightness of a star at a standard distance can be represented using absolute magnitude
8.12 draw the main components of the Hertzsprung–Russell diagram (HR diagram)
7.24 describe nuclear fusion as the creation of larger nuclei resulting in a loss of mass from smaller nuclei, accompanied by a release of energy
7.25 know that fusion is the energy source for stars
7.26 explain why nuclear fusion does not happen at low temperatures and pressures, due to electrostatic repulsion of protons
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Key Words
Key Word Image Definition
Black Dwarf A black dwarf is a white dwarf that has cooled sufficiently that it no longer emits significant heat or light
Black Hole A region of space having a gravitational field so intense that no matter or radiation can escape
Comet A celestial object consisting of a nucleus of ice and dust and, when near the sun, a ‘tail’ of gas and dust particles pointing away from the sun
Electrostatic Repulsion
The force experienced by a charged particle when it moves close to another particle of the same charge i.e. Two protons both repel as they are both positive.
Fusion The creation of a heavier nucleus by combining two smaller Nuclei. This process requires a large amount of energy to overcome electrostatic repulsion.
Gravitational Force
The attraction force between two objects due to their masses
Main sequence star
A star in its main stable period
Nebula A cloud of gas and dust in outer space
Neutron A sub atomic particle found in the nucleus. It has no charge and is similar in size and mass to a proton.
Neutron Star A celestial object of very small radius (typically 30 km) and very high density, composed predominantly of closely packed neutrons
Nucleus The centre/core of an atom. Contains neutrons and protons. Has a positive charge.
Radioactive Decay
The emission of an Alpha/Beta Particle, Neutron, or Gamma Ray from an unstable nucleus. This can make the nucleus more stable
Red Giant A very large star of high luminosity (brightness) and low surface temperature
Star A star is a celestial body that consists of a luminous sphere of plasma held together by its own gravitational field.
Supernova A star that suddenly increases greatly in brightness because of a catastrophic explosion that ejects most of its mass.
Universe All of space and time and their contents, including planets, stars, galaxies, and all other forms of matter and energy
White Dwarf A small very dense star that is typically the size of a planet
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α ParticleUnstable Nucleus
1:Star Classification and the Birth of Stars
Learning Outcomes:
1. Understand that the temperature of a Star affect the colour of its surface 2. Understand that stars can be classified by this colour. 3. Describe the process that leads to the birth of a star
Knowledge and Understanding QuizUse the knowledge you gained in Shell to answer the following questions.
1. What is a Solar System?
……………………………………………………………… (1)
2. If the mars rover travels at 0.5m/s, how long would it take it to travel 1km?
…………… (3)3. What force causes planets to orbit stars?
……………………………………………………………… (1)
4. Sketch the orbital shapes for the following objects and add a correct tail to the comet.
(3)
5. Plant X takes 12 weeks to orbit a star with an orbital radius of 650 million kilometres.
What is the orbital speed of Planet X in km/s?
…………… (3)
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Comet and Sun Moon and Planet
Score [ /11]
Star Classification
Star Classification Surface Temp [K] Colour Illustration
O More than 33000 Blue
B 33000 – 10000 Blue-white
A 10000 – 7500 White
F 7500 – 6000 Yellow-white
G 6000 – 5200 Yellow
K 5200 – 3700 Orange
M 6700 - 2000 Red
Key Ideas
1. Stars can range in temperature from 2000K (1727oC) to more than 33,000K (32,727oC)
2. When stars are at their hottest their surface is blue (like the centre of a Bunsen Burner)
3. Colder stars are Orange/Red (like a safety flame)4. The table above can be used to see how these are classified.
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5. Stretch: Stars can also be given a secondary classification from 0-9 (e.g. G5 would be half way between G and K)
The Birth of a Star – Comprehension ExerciseRead the text below on the formation of stars and use it to answer the questions. To help y
ou focus while reading the text do make use of underlining/highlighting.
For example:
Highlight key words in yellow Highlight key definitions in pink. Underline words you are unsure of and would like to look up afterwards.
The starting phase for all stars, including our Sun, begins when a dense region in a nebula starts shrinking and warming up. This is usually the result of one of several events that may occur to initiate the gravitational collapse of a molecular cloud. The means by which this occurs include galactic collisions or a devastating nearby supernova explosion sending ruptured matter into the clouds at very high speeds. Each of these stellar maternity wards can form anything from a few dozen to thousands of stars.
To form a star like our Sun, which is 864,400 miles (1,391,000 kilometres) across, it would take a collection of gas and dust a hundred times the size of our solar system. This is just the beginning. Once such a large amount of gas and dust huddle together, they form what we call a protostar. An object is considered a protostar for as long as material is still falling inward. For our Sun, and stars of the same mass, the protostar phase would have ended after approximately 100,000 years. After this, the protostar stops growing and the disk of material surrounding it is destroyed by radiation.
If the protostar was unsuccessful in acquiring enough mass, a brown dwarf will come into shape. These poor little guys are substellar objects that are unable to sustain hydrogen fusion reactions in their cores, due to their insufficient mass. Main sequence stars have no issue with this, to the envy of brown
dwarfs. Putting it simply, a brown dwarf is too big to be called a planet, and too small to be called a star. Until 1995, they were only a theoretical concept. It is now thought, however, that there is a brown dwarf for every six stars.
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The following link to a video is also an excellent resource to expand and develop your knowledge:
www.youtube.com/watch?v=mkktE_fs4NA
Questions
1. Mark the following statements as True or False according to the text:
STATEMENT TRUE FALSE
a. The starting phase for all stars begins when a region in a nebula starts shrinking and warming up.
b. A supernova explosion can form just one star.c. A brown dwarf is too small to be called a planet.
d. There is a brown dwarf for every six stars.
2. How do stars begin to form?
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3. What is a protostar?
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4. How long did the protostar phase last for our Sun?
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5. What happens if the protostar fails to gather enough mass?
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6. How many brown dwarfs are there in our universe?
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In the space below, write down the words you had to look up along with their definitions. This will be very useful during revision!
1. ……………………
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2. ……………………
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2: Evolution of Stars
Knowledge and Understanding QuizUse the knowledge you have gained in the previous 3 lessons to answer the following questions:
1. Describe the shape of a Satellite orbit.
……………………………………………………………… (1)
2. Give an example of a vector quantity.
……………………………………………………………… (1)
3. Moon X orbits Planet Y. It has an orbital radius of 54,000 km and each orbit takes 26
days. What is the speed of Moon X is km/s?
………………………. (4)
4. An object accelerates from rest (0m/s) to 25m/s in 8s. What is the acceleration of this
object?
……………………….(3)
5. Our Sun is about 5700K at it’s surface. What colour would you expect a star to be
that was much colder than this?
……………………………………………………………… (1)
Score [ /10]
Stars and Fusion – Science (Physics) 8
Learning Outcomes:
1. Describe the different evolution paths of stars. 2. Define the terms Supernova, Black Hole and Neutron Star3. Identify the differences and similarities between the evolutions of stars the size
of our sun and stars larger than out sun.
The Life Cycle of Stars – Comprehension ExerciseRead the text below on the life cycle of stars and use it to answer the questions. To help you focus while reading the text do make use of underlining/highlighting. [Note: This follows on from the content on ‘The Birth of a Star’.
For example:
Highlight key words in yellow and highlight key definitions in pink. Underline words you are unsure of and would like to look up afterwards. You may also life to write little reminders and notes in the margins to help you find
key points in the passage.
If the star is big enough to fuse hydrogen atoms into helium, it will enter the phase that our Sun is in, called the main sequence phase. A star will enjoy most of its life in the main sequence phase. At this point nuclear fusion is turning hydrogen into helium. The star is only stable because the light pressure of this energy balances out the star’s gravitational collapse.
Approximately nine out of ten stars in the universe are main sequence stars. These stars can range from around a tenth of the mass of our Sun all the way up to 200 times as massive, and how long a star will stay in the main sequence phase depends on its size. A star with higher mass might have more material to play around with, but it will burn faster due to higher core temperatures caused by greater gravitational forces. A star the size of our Sun will spend about 10 billion years in this phase, but a star 10 times the size of our own will stick around for only 20 million years.
After the main sequence phase, the star will become a red giant. A red giant is a dying star in one of the last stages of stellar evolution. In a few billion years’ time, our Sun will die and expand, gobbling up the inner planets, and maybe even the Earth (don’t worry; we’ll have died out a few billion years earlier. If we do manage to survive for another billion years, the temperature of the Earth’s surface will become far too hot for us humans.
After stars stop converting hydrogen into helium via nuclear fusion, gravity will take over. It’s all downhill from there though! Red giant stars reach sizes of 62 million to 621 million miles in diameter (100 million to 1 billion kilometres), 100 to 1,000 times the size of the sun today. The energy of the star is spread out across a larger area, like the pixels when one expands a raster graphic. Because of this, the star actually becomes cooler reaching only a little more than half the heat of the Sun. The
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temperature change causes stars to shine more towards the red part of the spectrum; it is this that gives a red giant its name.
Where a star goes from this point depends on its size. Let’s first go with the less violent option. Smaller stars, up to around eight times the mass of our sun, can become a white dwarf. These old stellar remnants are incredibly dense. A teaspoon of their matter would weigh as much on Earth as an elephant – that’s 5.5 tons in one incredibly strong teaspoon. A white dwarf’s radius is just .01 times that of our Sun, but the mass is about the same. Estimating how long a white dwarf has been cooling, helps astronomers increase their understanding of how old the universe really is.
After an unimaginable amount of time – tens or even hundreds of billions of years – a white dwarf will cool until it becomes a black dwarf, which is invisible because it is emitting at the same temperature as the microwave background. Because of the age of the universe and what we know about its oldest stars, there are no known black dwarfs.
Alternatively, a star with at least eight solar masses will have a much more violent, yet much more beautiful, death. Massive stars can create a supernova when they run out of fuel. To them, it’s better to go out with a bang than to fade away. When supernovae explode, they fling their guts into space at speeds of 9,000 to 25,000 miles per second.
These blasts produce much of the material in the universe including some heavy elements such as iron, which help to make up both ourselves and our planet, so all of us carry the remnants of these explosions in our bodies. As Neil deGrasse Tyson puts it, “It is quite literally true that we are stardust.” The cycle starts all over again, with a new generation of stars, and new stars are born from the stardust left behind in the same way.
That doesn’t mean it’s the end of the road for what remains of the star. After the supernova explosion, the star’s core is left behind in the form of either a black hole or a neutron star, both of which are incredibly destructive and violently beautiful. Neutron stars are hard to find and are very mysterious objects. They may only be about the size of a city, but don’t let that fool you, these objects are not to be messed with. They are extremely dense: if one
takes the mass of our sun, doubles it, and then shrinks it down to the size of Los Angeles, that’s roughly how dense a neutron star is. A cubic metre of a neutron star would weigh just less than 400 billion tonnes. All of that density makes their surface gravity truly immense.
Alternatively, what’s left after the supernova can become a black hole. Black holes literally pull the space around them. They need to have a massive amount of mass in an incredibly small space to have the required gravity to pull in light. To put this into perspective, to make a black hole out of the Earth the entire planet would need to be squeezed down to the size of a pea! These mysterious and frightening objects
Stars and Fusion – Science (Physics) 10
can slow down time and rip you apart and nothing can escape the grasp of a black hole when it reaches its event horizon. Any matter that enters its path is never seen again. They’re the playground bully of the universe, but unlike playground bullies, we might depend on them to live. Some researchers think black holes actually help create the elements because they break down matter into subatomic particles.
These particles make up you and I, and everything around us. We owe the stars our lives. Whether it’s big or small, young or old, you can’t argue that stars are some of the most beautiful and poetic objects in all of creation. Next time you look up at the stars, remember, you are part of them and now you know how it all started and how it ends!
Questions
1. Mark the following statements as True or False according to the text:
STATEMENT TRUE FALSE
a. A star will enjoy most of its life in the main sequence phase.
b. Nine out of ten stars in the universe are main sequence stars.c. A star with higher mass will burn slower.
d. After the main sequence phase, the star will become a red giant.
e. In a few billion years’ time, our Sun will die and expand, gobbling up the inner planets.
f. After tens or hundreds of billions of years, a white dwarf will cool until it becomes a black dwarf.
g. After the supernova explosion, a star’s core becomes either a black hole or a neutron star.
h. What’s left after the supernova can become a brown dwarf.
2. Approximately how many main sequence stars are there?
………………………………………………………………………………………………………
3. What determines how long a star will stay in its main sequence stage?
………………………………………………………………………………………………………………………………………………………………………………………………………………
4. What will happen to our Sun after the main sequence phase?
………………………………………………………………………………………………………………………………………………………………………………………………………………
5. How much can a red giant expand?
………………………………………………………………………………………………………
Stars and Fusion – Science (Physics) 11
6. How dense are white dwarfs?
………………………………………………………………………………………………………
7. Why are black dwarfs invisible?
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8. How do massive stars die?
………………………………………………………………………………………………………………………………………………………………………………………………………………
9. What happens to a star’s core after a supernova explosion?
………………………………………………………………………………………………………………………………………………………………………………………………………………
10. What can black holes do?
………………………………………………………………………………………………………………………………………………………………………………………………………………
11. Match the terms to their definitions:
� approximately
� collision
� dense
� destructive
� emit
� escape
� fling
� frightening
� fusion
� gobble up
� grasp
� huddle
� immense
� initiate
� phase
� rip
� rupture
� surface
1. a breaking apart2. a union by or as if by melting3. about4. catastrophic5. clash6. give off7. having a high mass8. humongous9. period10.scary11.start12.swallow up 13. the exterior or upper boundary of an object or body14. to crowd together15. to get away16. to take or seize eagerly17. to tear or split apart or open18. to throw forcefully
Stars and Fusion – Science (Physics) 12
In the space below, write down the words you had to look up along with their definitions (if they are not listed above!). This will be very useful during revision.
1. ……………………
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2. ……………………
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3. ……………………
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4. ……………………
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Summary: Life Cycle of Stars
Comparing the Evolution of StarsUsing your knowledge and the diagram below can you identify the similarities and differences in the evolution of stars the size of the sun and stars bigger than the sun.
Similarities Differences
Stars and Fusion – Science (Physics) 15
Writing Task – The Life Cycle of a Star
In this task you are going to write about the Life Cycle of a Star the size of our Sun (from birth to black dwarf).
You have creative license and may write your answer as:
a. A simple description you may find in a textbookb. A creative piece told from the point of view of the starc. A dystopian piece told from the point of view of Planet Earth (harder!)
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Markers Comments:
Stars and Fusion – Science (Physics) 16
3: Luminosity and the Hertzsprung - Russell diagram
Investigation Write-Up Practice
Describe and experiment to measure the density of a rock. In your answer you should
include:
Equipment used for each measurement
Instructions to be followed during the investigation
Steps that should be taken to ensure accurate results.
You may draw a diagram to support your answer.
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Score [ /6]
Learning Outcomes:
1. Define the absolute brightness of a star2. Describe the factors that affect the apparent brightness of a star3. Sketch and interpret the Hertzsprung Russell diagram (HR diagram)
Stars and Fusion – Science (Physics) 17
The Brightness of Stars
Absolute Brightness
Apparent Brightness
Key Ideas
1. How bright a star looks from Earth depends on:a. The distance the star is from Earth.b. What the star is made from and the kind of nuclear reactions taking place
inside the star2. Astronomers describe the brightness of a star in three different ways:
a. The apparent brightness or magnitude: simply a measure of how bright the star looks from Earth
b. The absolute brightness or magnitude: a measure of how bright the stars would be if they were all the same distance from Earth (good for comparing stars)
c. The luminosity: measures how much energy in the form a light that is emitted from the star’s surface every second.
3. The Hertzsprung–Russell diagram, abbreviated as HR diagram, is a scatter plot of stars showing the relationship between the stars' absolute magnitudes [From +15 to -5] versus their stellar classifications or temperatures (see next page). It is a key tool when studying stellar evolution.
Stars and Fusion – Science (Physics) 18
Stars and Fusion – Science (Physics) 19
Questions on the Hertzsprung-Russell Diagram
Use your HR diagram to answer the following questions.
1. To what group of stars does the Sun belong? How do you know?
……………………………………………………………………………………………………….……………………………………………………………………………………………………….
2. How does Absolute Magnitude (Brightness/Luminosity) relate to Temperature within the Main Sequence? Does it increase or does it decrease?
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3. What types of stars have LOW absolute magnitude but a HIGH temperature?
……………………………………………………………………………………………………….
4. Why types of stars have HIGH absolute magnitude but LOW temperature?
……………………………………………………………………………………………………….
5. Sketch and label the general shapes of the HR diagram in the space below. You will need to know these for your exam.
** Top Exam Tip: Try to remember the general features of the HR diagram – the shape and position of the main sequence, white dwarfs, red giants and super giants ***
Stars and Fusion – Science (Physics) 20
Exam Style Questions
Stars and Fusion – Science (Physics) 21
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STRETCH available on pages 39 and 40
Stars and Fusion – Science (Physics) 24
4: Radioactivity Revision and Energy in Stars
Knowledge and Understanding Check - RadioactivityHow much can you remember from the Remove topic on Radioactivity? Complete the summary sheet below.
Term Definition
Atomic Number
Mass Number
Isotope
Ionisation
Half Life
Contamination
Irradiation
Add the labels to the diagram below:
Radiation Symbol Form Penetrative Power
Ionisation Ability
Alpha
Beta
Gamma
Neutron
Stars and Fusion – Science (Physics) 25
Stars and Fusion – Science (Physics) 26
Learning Outcomes:
1. Review and recap content from the radioactivity topic. 2. Describe Fusion, the process by which stars create energy. 3. Explain why Fusion can only happen in stars.
Radioactivity Summary WorksheetUse the summary sheet on page 5 to attempt the questions on the worksheet.
1. Where does nuclear radiation come from? [1]
……………………………………………………………………………………………………….
2. What are alpha particles made up of? [2]
……………………………………………………………………………………………………….
3. What would you use to stop the following forms of radiation? [3]a. Alpha
……………………………………………..
b. Beta
……………………………………………..
c. Gamma
……………….…………………………….
4. Explain what is meant by ionizing radiation. [2]
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5. Why is gamma radiation used as a tracer in the body rather than alpha radiation? [2]
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6. Use he graph to calculate the half life of a sample. [3]
……………………….
Stars and Fusion – Science (Physics) 27
time (days)
counts per m
7. Carbon -14 has a half-life of 5,700 years. If a sample of freshly cut wood has a count rate of 10 counts per minute, and a second piece of wood has a count rate of 2.5 counts per minute, how old is the second piece of wood? [3]
……………………….
8. Would long or short half-life materials be appropriate in the following situations? [6]
9. Complete the following decay equations by balancing the atomic numbers and mass numbers on each side of the equation. [9]
Po84204 → ❑❑
200 + α❑❑
P→1532 S❑
❑ + β❑❑
Pb→82209 ❑❑
208 + n❑❑
10. What new element is formed following the beta decay of dysprosium-165? [5]
Score [ /36]
Stars and Fusion – Science (Physics) 28
What is Fusion?
Key Ideas:
1. Fusion is the creation of a (large) nucleus from smaller nuclei. 2. When the smaller nuclei fuse together, their total mass decreases. 3. This process also releases a large amount of kinetic energy.
Stars and Fusion – Science (Physics) 29
Fusion in Stars
Label on the key components of nuclear fusion in stars on the diagram below:
Complete the sentences below:
Two ___________ of Hydrogen ( ___________ and ___________ ) collide at very high
_________.
They undergo ________ to form a ____________ nucleus, a neutron and a large amount of
_________ ____________.
The mass of the products of fusion is _________ than the two _________ isotopes that
were used in the process.
Fusion is the energy source for our ________ and all other ______ in the Universe.
Stars and Fusion – Science (Physics) 30
The Difficulties with Fusion
Key Ideas:
1. For Fusion to happen the deuterium and tritium nuclei must collide with enough energy to overcome the electrostatic repulsion between the protons in the nuclei.
2. Requires very high temperatures to give deuterium and tritium enough kinetic energy.
3. This high temperature liquid (100 million oC) must be kept in a strong magnetic field (‘magnetic bottle’).
4. To increase the chance of fusion this hot liquid must be kept under very high pressure.
5. This high pressure allows the nuclei to be close enough together to collide.
Stars and Fusion – Science (Physics) 31
Worksheet – Nuclear Fusion
Use the knowledge you have gained this lesson to answer the following questions.
1. How is nuclear fusion different to nuclear fission?
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2. What elements are fused together in the Sun and what new element does this produce?
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3. Why can nuclear fusion happen in the sun?
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4. The main fusion reaction that could be used here on Earth is:
Explain what this reaction means.
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5. JET is an experimental fusion reactor near Oxford. It has not been able to produce large
amounts of nuclear fusion. Why is it so difficult to get fusion reactions to work?
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6. What would be the source of the fuel required by a fusion reactor?
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Score [ /13]
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Stretch Worksheet – The Evolution of Stars Can you use the information on pages 24, 27 and 28 to attempt the cross word below.
Stars and Fusion – Science (Physics) 33
Stretch Worksheet – Black Holes
Black Holes are something of an Enigma inspiring a number of Science Fiction works including the 2014 award winning film ‘Interstellar’.
Use your MacBook to do some research to see if you can come up with answers to some of the more frequently asked questions about Black Holes.
1. Is it possible for black holes to lead to other universes?…………………………………………………………………………………………………..…………………………………………………………………………………………………..…………………………………………………………………………………………………..…………………………………………………………………………………………………..…………………………………………………………………………………………………..…………………………………………………………………………………………………..…………………………………………………………………………………………………..…………………………………………………………………………………………………..
2. What happens to all the stuff that gets sucked into the black hole?…………………………………………………………………………………………………..…………………………………………………………………………………………………..…………………………………………………………………………………………………..…………………………………………………………………………………………………..…………………………………………………………………………………………………..…………………………………………………………………………………………………..…………………………………………………………………………………………………..…………………………………………………………………………………………………..
3. What would happen if two black holes got too close together?…………………………………………………………………………………………………..…………………………………………………………………………………………………..…………………………………………………………………………………………………..…………………………………………………………………………………………………..…………………………………………………………………………………………………..…………………………………………………………………………………………………..…………………………………………………………………………………………………..…………………………………………………………………………………………………..
4. Could a black hole's gravity be reversed so that it spit everything back out into the universe?…………………………………………………………………………………………………..…………………………………………………………………………………………………..…………………………………………………………………………………………………..…………………………………………………………………………………………………..…………………………………………………………………………………………………..…………………………………………………………………………………………………..…………………………………………………………………………………………………..…………………………………………………………………………………………………..
Stretch Activity: The Advantages of using Fusion
Stars and Fusion – Science (Physics) 34
Use your MacBook and/or Textbooks to research the possible advantages to using Fusion as an Energy Resource.
[Stuck: Try visiting the websites below to get you started!]
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https://www.iter.org/sci/Fusion
http://fusionforenergy.europa.eu/understandingfusion/merits.aspx
http://www.ccfe.ac.uk/introduction.aspx
Stars and Fusion – Science (Physics) 35
Stars and Fusion
Past Paper Questions
Stars and Fusion – Science (Physics) 36
Q1. (a) Which of these objects orbits a planet?
(1)
A comet
B dwarf star
C galaxy
D moon
(b) What is the correct name for our galaxy?
(1)
A Crab Nebula
B Milky Way
C Solar System
D Universe
(c) Which of these objects has the largest mass?
(1)
A artificial satellite
B comet
C Earth
D Sun
(d) Which of these stars is the coolest?
(1)
A blue star
B orange star
C red star
D yellow star
(Total for question = 4 marks)
Stars and Fusion – Science (Physics) 37
Q2.
Main sequence stars can vary in brightness, colour and mass.
Describe the evolution of both low mass stars and high mass stars after they join the main sequence.
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(Total for question = 6 marks)
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Q3.
This is a question about nuclear energy.
(a) Nuclear fusion can take place between different isotopes of hydrogen to produce an isotope of helium.
(i) Complete the nuclear equation for this process.(2)
(ii) This process also results in the release of energy.State where the fusion process takes place naturally.
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(iii) Explain why the isotopes of hydrogen must be heated to a very high temperature for fusion to take place.
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(b) Nuclear fission also results in a release of energy.
Explain how nuclear fission differs from nuclear fusion.(2)
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(Total for question = 8 marks)
Stars and Fusion – Science (Physics) 39
Q4.
The Sun is a main sequence star.
In the Sun, hydrogen nuclei are changed into helium nuclei, releasing energy.
(a) Name the process that changes hydrogen into helium.
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(b) Describe the evolution of the Sun when it leaves the main sequence.
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(c) The Sun's core has a mass of approximately 7 × 1029 kg.
Approximately 75% of the mass of the core is hydrogen.(i) Calculate the approximate mass of hydrogen in the Sun's core.
(1)
mass of hydrogen = ........................................................... kg
(ii) When most of the hydrogen nuclei in the Sun's core have been changed intohelium nuclei the Sun will leave the main sequence.The Sun's core loses approximately 9 × 1019 kg of hydrogen each year.Estimate the time until the Sun leaves the main sequence.Give your answer to one significant figure.
(2)
time = ........................................................... years
(Total for question = 6 marks)
Stars and Fusion – Science (Physics) 40
Q5.
The International Space Station (ISS) is a satellite that orbits the Earth at a height of 409 km above the surface of the Earth.
The ISS has an orbital speed of 7.66 km/s and a period of 92.7 minutes.
(a) (i) Calculate the orbital radius of the ISS.
Give your answer to 3 significant figures.(4)
orbital radius = ........................................................... km
(ii) Calculate the radius of the Earth using your value for the orbital radius.(1)
Earth radius = ........................................................... km
(Total for question = 5 marks)
Stars and Fusion – Science (Physics) 41
Stars and Fusion
Spec Point Notes
Stars and Fusion – Science (Physics) 42
Stars and Fusion Specification Notes
8.07 understand how stars can be classified according to their colour
8.08 know that a star’s colour is related to its surface temperature
Stars are classified into 7 groups according to their colours (which is due to their surface temperature); O,B,A,F,G,K,M O are hottest (> 33 000 K and blue), M are coolest (2000 – 3700K and red)8.09 describe the evolution of stars of similar mass to the Sun through the following stages:
• nebula
Stars form from large clouds of dust and gas particles (nebulae) that are drawn together by gravitational forces over millions of years. As the particles get closer the temperature and pressure becomes so large that nuclear fusion of hydrogen nuclei to helium nuclei occurs. This releases enormous amounts of energy in the form of heat and light.• star (main sequence)
Fusion produces forces that make the star expand outwards, but gravitational force is always pulling the particles within the star inwards. When these two opposing forces become balanced a star is stable and called a main sequence star. It should stay this way for millions of years, at a constant size and temperature.• red giant
Eventually hydrogen fusion stops as the star runs out of fuel. Gravitational force is now bigger than the outward fusion force which causes the star to collapse inwards and compress. This causes it to heat up to even higher temperatures so that fusion of helium nuclei begins. The increased power output causes the star to expand greatly. The surface area is so large that it
Stars and Fusion – Science (Physics) 43
is cooler than before, so its colour changes to red and the star is called a red giant.• white dwarf
Eventually fusion stops when the star runs out of helium nuclei and the gravitational force causes the star to collapse inwards and compress again. This heats it up so it changes colour to emit white light. The star is squashed so greatly by the gravitational force to become a small and very dense white dwarf. (They are so dense that a teaspoon full would weigh more than a cruise liner). A white dwarf eventually cools down and change colour as it does so, eventually becoming black.
8.10 describe the evolution of stars with a mass larger than the Sun
After the stable period, a giant star expands into red supergiant. (It produces all the elements up to iron during nuclear fusion). When it finally runs out of nuclei to fuse it collapses due to the gravitational force, and then explodes – an exploding star is called a supernova.The explosion throws dust and gas back into space and so another nebula is formed. A dense core remains – called a neutron star, because it is made entirely from neutrons. If its mass is large enough it can compress further to become a black hole. (Their gravity is so strong that not even light can escape !)
8.11 understand how the brightness of a star at a standard distance can be represented using absolute magnitude
Apparent magnitude is simply how bright a star appears in the night sky. But, the brightness of a star depends on its distance from Earth and its luminosity – how much power it produces. (A dim star could just be very far away, or very close but not very luminous).Absolute magnitude enables us to compare the brightness of stars because it is a measure of how bright they would appear if they were all the same distance from the Earth. – 32.6 light years.
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8.12 draw the main components of the Hertzsprung–Russell diagram (HR diagram)
This diagram shows the relationship between a star’s luminosity (its brightness or power output) and its surface temperature. A star moves to different positions in the diagram during its life, as its internal structure and temperature change.
Important Note: the temperature scale is reversed. It is hotter towards the
origin of the x axis.7.24 describe nuclear fusion as the creation of larger nuclei resulting in a loss of mass
from smaller nuclei, accompanied by a release of energy
Fusion occurs when smaller nuclei combine… (isotopes of Hydrogen)
to create a larger nucleus.
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Mass is lost in the process and vast amounts of energy are released.
7.25 know that fusion is the energy source for stars
7.26 explain why nuclear fusion does not happen at low temperatures and pressures, due to electrostatic repulsion of protons
v
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