science gcse core, additional and triple powerpoints

1. P7 Physics ‘triple science’ Route map Over the next 24 lessons you will study: Friday 21 October 2011 P7.1 What is a telescope P7.2 Describing lenses P7.3 Refracting telescopes P7.4 Reflecting telescopes P7.5 Radio telescopes P7.7 Images of stars P7.8 The Sun, Moon and Earth P7.9 Observing the skies P7.10 Eclipses P7.11 Star distances P7.12 Star brightness P7.6 Ray diagrams P7.14 Galaxies-cepheid variable stars P7.15 Galaxies one or many P7.13 Star temperatures P7.16 Mapping the Milky Way P7.17 The changing Universe P7.18 Our Sun P7.19 The composition of stars P7.20 Emission spectra P7.21 Atoms and nuclei P7.22 Nuclear fusion P7.23 Behaviour of gases part one P7.24 Behaviour of gases part two P7.25 Types of stars P7.26 Structure of our Sun End of module test P7.27 Protostars P7.28 Star death

3. Extension questions: 1: Name some of the types of radiation in the electromagnetic spectrum and put them in order of increasing frequency ? 2: Give one use of a) infra red b) X-rays, c) Gamma waves and d) microwaves ? 3: Our star is a bright yellow colour. Estimate its surface temperature using the above information ? 4: Using the example of a filament light bulb explain how the filament changes colour as it gets hotter ? Know this: a: Know how the radiation given off by a star is linked to its surface temperature b: Know the different types of radiation in the electro-magnetic spectrum, for example UV, IR, X-rays and microwaves. Friday 21 October 2011 Introduction: Stars produce a constant stream of radiation which consists of a wide range of different frequencies. Most of the emitted radiation from stars is in the infrared (IR), visible and ultraviolet (UV) range of the electromagnetic spectrum. Not all stars are have the same appearance in the night sky. When you look carefully it can be seen that stars shine with different colours ranging from red to white. A star’s colour is dependant on the star’s surface temperature. A star with a red colour is at the cooler end with a surface tempearture of around 2000 o C. A star with a violet colour is at the hotter end with a surface temperature of 1500 o C. P7.13 Star temperatures

4. Key concepts Look at the photograph and information and answer all the questions: How does the a) frequency and b) the wave speed change from radio waves to gamma rays ? Explain what happens to the penetration ability as you move form radio waves to gamma waves ? Doctors exploit the penetrating ability of which wave to examine broken bones ? Electromagnetic waves are transverse waves which travel at a speed of 300,000 kms -1 through a vacuum. This is usually called the speed of light. All e.m waves transfer energy from one place to another and like visible light can be reflected by smooth, hard surface or refracted when they travel form one material to another. through transparent materials. The electromagnetic spectrum 10 -9 m 10 -6 m 10 -3 m 1 10 3 m 10 6 m 10 9 m Photon energy (J) Increasing energy and penetration Photons and the electromagnetic spectrum P7.13 a

5. Key concepts Look at the photograph and information and answer all the questions: Look at the picture above its shows the night sky which of course is actually one spiral arm of our own Galaxy the ‘Milky Way. Away form large cities and light pollution, you can see amazing array of different stars. The overall luminosity of a star will depend on its mass and distance from us. Its colour will depend on its surface temperature. The sun’s surface temperature is about 5000 °C what colour is it ? In the second picture which end of the colour spectrum would you find a hot star and which end would you find a colder star? 1000 °C 15000 °C 5000 °C P7.13 b Star temperatures

6. Key concepts Look at the photograph and information and answer all the questions: Billions of stars, found in millions of galaxies, but how do we identify groups of similar stars ? The new system reordered the classes into the order OBAFGKM where O stars are the hottest and each successive class is cooler with M being the coolest stars. Each letter was also divided into tenths of the range by adding a number 0-9 to the end. O stars are the least common and M are the most common found in the main sequence of stars. Look at the above diagram, estimate the surface temperature in o C of our own star, the sun ? Explain why larger or brighter stars often only last a few million years when compared to an average star like our own sun ? P7.13 c Star temperatures Type Colour Temp. Range % of stars Examples O Blue-violet >30,000 K 0.00003% Stars of Orion’s Belt B Blue-white 10,000 K - 30,000 K 0.13% Rigel A White 7,500 K - 10,000 K 0.6% Sirius F Yellow-white 6,000 K - 7,500 K 3% Polaris G Yellow 5,000 K - 6,000 K 7.6% Sun K Orange 3,500 K - 5000 K 12.1% Arcturus M Red-orange <3,500 K 76.5% Proxima Centauri

7. Key concepts P7.14 d Look at the photograph and information and answer all the questions: Looking at star brightness The area under the graph is an indication of star luminosity. The greater the area the hotter the star. At frequency X the two stars have different peak frequencies. The higher the peak at frequency X the hotter the star. The hotter the star the higher the peak frequency which means it has a higher proportion of radiation at higher frequencies. Look at the graph opposite left, which line on the graph show a hotter star? Which line on the graph shows data from a less luminous star ? Which line on the graph shows a star with a higher peak frequency ? Frequency Intensity of radiation hottest star coolest star UV light Infra red

8. P7.13 Plenary Lesson summary: Frequency violet surface colour Friday 21 October 2011 How Science Works: Research into the difference between our sun and a unique type of star which can vary both its luminosity and surface temperature called a ‘cepheid variable star.’ Preparing for the next lesson: The ________ of a star indicates how hot the _________ temperature is. The hotter the star the colour will be at the _________ end of the visible spectrum. On a graph of __________ against intensity a hotter star show higher peak frequency and luminosity (area under graph). Imagine living on Earth about 4.5 billion years into the future, you will see in the morning sky the sun turn red increasing rapidly in size. Eventually the red giant will increase and engulf even our planet instantly vapourise any surface life and water. What will be left will be a rocky planet devoid of any life and of course a cold planet without a sunrise or sunset . Decide whether the following statements are true or false : False True 3: Hotter stars tend to emit larger quantities of infra red radiation ? False True 2: A star’s luminosity is dependant on both its distance and size ? False True 1: Stars with a greater surface temperature will be red ?

10. Extension questions: 1: Would a bright star have a higher or lower luminosity ? 2: Would a dim star have a higher or lower temperature ? 3: Would a dim star have a larger or small diameter ? 4: Why was it important that stars in the same galaxy are studied and compared when studying cepheid variable stars ? 5: Explain why astronomers are inserted in the distance between the milky way and other galaxies ? Know this: a: Know the relationship between brightness and period for Cepheid variable stars. b: Know how this relationship mean that we can calculate star distances. Friday 21 October 2011 Introduction: Most stars burn at a steady rate there are a few which don’t, they are called Cepheid variable stars. These stars, first seen in 1784, vary in brightness. Over a period of time they go from bright to dim and back again. These stars are actually expanding and contracting which then changes its luminosity and temperature. The diameter of these stars can change by up to 30%. Henrietta Leavitt studied these stars in nearby galaxies and saw a pattern between, the time it took to expand and contract back, and its luminosity. If you can calculate a star’s luminosity then you can then go on to calculate its distance from Earth. P7.14 Galaxies – cepheid variable stars

11. Key concepts P7.14 a Look at the photograph and information and answer all the questions: How long is the period of variation for the above star ? The graph shows a Cepheid variable star. The star gets dimmer and then returns to its original brightness. The length of time (called a single period) it takes to do this is important as this information can be used to calculate its luminosity. The time it take to go dim and then return to original brightness is called the period of variation . Time (days) Observed brightness A Cepheid variable star As a star’s luminosity varies over a single period, will its surface temperature also vary over the same time period ? 1 0 2 3 4 7 6 5

12. Key concepts P7.14 b Look at the photograph and information and answer all the questions: Explain what happens to the star’s size, luminosity and surface temperature over the seven day period ? Cepheid stars oscillate between two states: In one state, the star is compact and large temperature and pressure gradients build up in the star. These large pressures cause the star to expand. When the star is in its expanded state, there is a much weaker pressure gradient. Without the pressure gradient to support the star against gravity, the star contracts and the star returns to its compressed state (see the above diagram) Time (days) brightness A Cepheid variable star Another star has a period of variation of 10 days, which star will have the highest luminosity on day 5 ? star diameter 1 0 2 3 4 7 6 5

13. Key concepts P7.14 c Look at the photograph and information and answer all the questions: Look at the four pictures taken on May 4 th to May 20 th when its this start at its large by diameter and smallest by diameter ? The four pictures above shows a Cepheid variable star. The star can be seen brightly on may 4 th but gets dimmer for a week and then returns to original brightness by may 20 th . Without the presence in the galaxies across the Universe of these Cepheid stars Hubble would not have been able to calculate the distances to other galaxies. How many days does this star take to do a variation cycle ? A Cepheid variable star May 4 th May 9 th May 16 th May 20 th

14. Key concepts P7.14 d Look at the photograph and information and answer all the questions: luminosity time period A D B C Place the four stars A-D into order with the brightest star first ? Why can star A have a greater luminosity than star B even though its smaller and less bright ? Luminosity versus time in a Cepheid star Star brightness can be easily seen and measured if the period of variation is also known then the luminosity can be calculated. Brightness of stars are assigned a number starting with the brightest star starting at about -1 magnitude. Dimmer stars are zero or positive numbers. The larger the number means the dimmer the star is. For example, a star -1 magnitude is brighter than a star 0 magnitude. A star 0 magnitude is brighter than a star 1 magnitude and so on Magnitude sequence for stars starting with the brightest is -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 magnitude, ... etc Looking at star brightness

15. P7.14 Plenary Lesson summary: period cepheid expands rate Friday 21 October 2011 Most stars are currently classified using the letters O , B , A , F , G , K and M (usually memorized by astrophysicists as &quot;O be a fine girl, kiss me&quot;), where O stars are the hottest and the letter sequence indicates successively cooler stars up to the coolest M class. According to an informal tradition, O stars are &quot;blue&quot;, B &quot;blue-white&quot;, A stars &quot;white&quot;, F stars &quot;yellow-white&quot;, G stars &quot;yellow&quot;, K stars &quot;orange&quot;, and M stars &quot;red.” How Science Works: Research into the current view of the Universe as a collection of billions of galaxies in constant expansion and look at the work of Harlow Shapely and Edwin Hubble. Preparing for the next lesson: There is a small group of stars that burn at a varying ______. These stars are called ______ variable stars, their diameter _________ and contracts over a certain ______ of time. This is the period of variation the longer this period is the more luminous the star. Decide whether the following statements are true or false : False True 3: In the contracted phase of a star its at its brightest ? False True 2: In the expanded phase of a star is at its dimmest ? False True 1: luminosity is linked to star temperature ?

18. Key concepts P7.15 a Look at the photograph and information and answer all the questions: Explain why this single picture taken over 10 days in 1998 has radically change the way we view our own Universe ? It is estimated that some of the galaxies picture above are up to 13 billion light years away. Explain why if life does exist there we may never know of its existance ? The Hubble telescope launched in 1996 by the shuttle program is in a fixed orbit outside the Earth’s atmosphere. Over the Christmas holidays in 1998 its camera was pointed at an area of space with no visible stars for 10 days. When the picture was sent to Earth it showed that this small part of deep space was full of galaxies. Each speck on the picture left is a galaxy contain up to 100 billion stars Hubble ‘deep space photograph in 1998

19. Assessment for learning...key concepts P7.15 a Look at the photograph and information and answer all the questions: Explain why the most common element found in the Eagle nebula is hydrogen gas which is the building material for all stars ? Explain why larger or brighter stars often only last a few million years when compared to an average star like our own Sun ? Billions of stars, found in millions of galaxies, filling billions of light years of space, but how are galaxies and stars formed. In 1998, the Hubble telescope and one of its many images, finally gave us spectacular evidence that tells scientists how stars and galaxies are formed. The Eagle nebula (pictured below) is a cloud of hydrogen and dust millions of light years across. At the end of each finger like protrusion, the gravitational forces form a ball of hydrogen. Huge gravitational forces superheat the hydrogen so that nuclear fusion begins, light is produced and a star is born.

20. P7.15 Plenary Lesson summary: disproved development telescope galaxies Friday 21 October 2011 In 1915 Harlow Shapley used Cepheids to place initial constraints on the size and shape of the Milky Way, and of the placement of our Sun within it. In 1924 Edwin Hubble discovered Cepheid variables in the Andromeda galaxy. That settled the debate, of whether the Milky Way was one of many galaxies that constitutes the Universe. How Science Works: Research into the nature of our own Galaxy, the Milk Way Preparing for the next lesson: The work of Shapley, Hubble and Curtis has been crucial in our understanding of the _________. They showed a clear _________ of theories until arriving at one which has not been _________. Hubble's work with Cepheid's and Andromeda was so important that they named a ___________ after him. Decide whether the following statements are true or false : False True 3: Shapley's work on nebulae turned out not to be correct ? False True 2: Hubble used Cepheid stars to calculate the brightness of different stars ? False True 1: Edwin Hubble designed the Hubble Space Telescope ?

22. Extension questions: 1: Explain why we will never have a true picture of the Milky Way ? 2: Name one star constellation found in the night sky ? 3: Galaxies are formed by massive clouds of dust and gases in space: a) What’s the force that attracts the clouds of dust and hydrogen gas together to form stars. b) Once formed, the star has a stable life for billions of years. 4: Describe the two main forces at work in the star during this period. c) What happens to the star once this stable period is over ? Know this: a: Know that the ‘Milky Way’ is just one of billions of galaxies that form our Universe. b: Know how Shapley’s and Hubble's work have helped us understand and improve the work of the previous scientists. Friday 21 October 2011 Introduction: Look up at the night sky and you are looking through a very small part of our own galaxy the Milky Way. Although light pollution in cities hinders our view of the sky at night, far away in the unpopulated countryside the Milky Way is awesome. Viewed at night you can see why it is named the Milky Way. A milky light crosses the sky, full of stars, all many hundreds of light years away. Our own galaxy stretches over 100,000 light years across. Our night sky moves around the pole star (named Polaris) P7.16 Mapping the Milky way

23. Key concepts P7.16 a Look at the photograph and information and answer all the questions: The Milky Way Galaxy, is the galaxy in which the Solar System is located. The Milky Way is a barred spiral galaxy that is part of the Local Group of galaxies. It is one of billions of galaxies in the observable universe. Some sources hold that, strictly speaking, the term Milky Way should refer exclusively to the band of light that the galaxy forms in the night sky, while the galaxy should receive the full name Milky Way Galaxy, or alternatively the Galaxy Explain why the two picture opposite are an artists impression rather than a real photograph ? Explain why most of the the mass of a galaxy (stars) is found towards its centre ? An average galaxy has about 100 billion stars, explain why life elsewhere is almost certain to exist but we may never know that it does ? The milky way

24. Key concepts P7.16 a Look at the photograph and information and answer all the questions: Explain why you cannot see the full beauty of the Milky Way in a city like London ? Why can the Polaris star been used to navigate at night ? A collection of stars, this five armed spiral galaxy is home to our Sun and its nine planets. Our own galaxy is vast, over 100,000 light year across. In cities and other populated areas we can only see a few stars because of light pollution. Time lapse photography shows us that the night sky revolves around a central star called Polaris. This star is used to navigate north because its position remains unchanged throughout the night. The Milky Way

25. P7.16 Plenary Lesson summary: centre spiral way years Friday 21 October 2011 Our own galaxy is vast, over 100,000 light year across. In cities and other populated areas we can only see a few stars because of light pollution. It is worth just once in your life to go to the rote countryside and see the full beauty of the Milky Way ! How Science Works: Research into how our Universe is expanding and Hubble constant Preparing for the next lesson: The Milky _____ is a five _______ Galaxy spanning just over 100,000 light _______ across. It is home to our solar system and of course planet Earth. The majority of the Milky way’s mass is found towards its _______. Decide whether the following statements are true or false : False True 3: The Sun is a the very centre of the Milky Way ? False True 2: It takes light 10,000 years to travel across the entire width of the Milky Way ? False True 1: The Milky Way is a four spiral Galaxy ?

28. Key concepts P7.17 a Look at the photograph and information and answer all the questions: What is the speed of recession when the distance is 20 mpc and the Hubble constant is 70 km/s per mpc? What are the units of all the term in the equation? Hubble used the early work of Leavitt to determine the distance of at least 10 galaxies. He also made another great discovering that all galaxies were moving away from. This produced a red shift which occurs when a light source is moving away. If galaxies were moving towards us a blue shift would happen. The Hubble constant took many years to find an accurate value but its now taken to be 72 ±8 km/s per MPC. Speed of = Hubble X distance Recession constant Distance (mpc) speed of recession (km/s) 10 6 2x10 6 1000 500 X X X X X X X The Hubble constant

29. Look at the photograph and information and answer all the questions: If all observable planets acquired a blue shift instead of a red shift what would this mean would be happening ? Explain why scientists cannot yet answer the question ‘will the Universe contract from its current size ? Since the ‘big bang’ the Universe continues to expand, but what other evidence do we have to support the big bang theory proposed by Stephen Hawking. If we observe the many thousands of visible galaxies using the Hubble telescope, they all have a red shift meaning that they are always moving away from us. These images proves that the Universe and its galaxies are in constant expansion. (If the galaxies has a blue shift they would be in contraction or moving towards us) Big bang the expanding Universe Key concepts P7.17 b Expansion Contraction Red shift Blue shift

30. Look at the photograph and information and answer all the questions: Why did Ptolemy and his peers in 140 AD think that the Earth was at the centre of the Universe ? Hubble's observation that the Milky Way was just one of many millions of galaxies was an important discovery…explain why ? Humans, for thousands of years have asked questions about their own history, the history of the solar system and Universe. Early philosophers and modern scientists have given us different answers to the one single question: How and when did the Universe begin ? Over the last two thousand years, many different theories have been offered by scientists to explain what events began, that led to the formation of the Universe and all the galaxies that we observe today . Ptolemy: Proposes in 140 AD that the Earth is a sphere and is at the very centre of the Universe. Copernicus: Proposes in 1600 AD that the Sun is the very centre of the Universe, with the Earth orbiting it. Hubble: Proposes that our galaxy, the Milky Way is just one of billions of similar Galaxies. Hawkins: Popularised that the Universe started with a big bang around 14 billion years ago and is still in constant expansion. Key concepts P7.17 c

31. P7.17 Plenary Lesson summary: red shift receding spectra Hubble Friday 21 October 2011 Hubble went on to discover many more stars in other nebulas located outside the Milky Way. Whilst studying these other galaxies he found that they contained many similar features of our own Milky Way Galaxy. He found they contained stars called novas that suddenly flair brightly and globular cluster, compact groups of stars. Hubble finally proposed his theory that nebulas where actually other galaxies much like our own. How Science Works: Research the composition of stars and the anatomy of our own star, the Sun Preparing for the next lesson: __________discovered that the universe is ___________ (moving apart). He did this by proving that the light given off by stars shifts over time to the red end of the visible _____ this is called the ______________ Decide whether the following statements are true or false : False True 3: Hubble's initial constant of 500km/s per mpc was correct ? False True 2: There’s a linear relationship between a star’s distance and speed of recession ? False True 1: 10 7 parsec = 1 megaparsec ?

33. Extension questions: 1: Explain what stars like the sun are formed from ? 2: What’s the force that attracts the clouds of dust and hydrogen gas together to form stars. 3: Give two forms of energy that is emitted by the Sun ? 4: What type of radiation can increase the risk of skin cancer ? 5: Why should you never look at the Sun directly or through telescope ? Know this: a: Know the composition and anatomy of stars like our sun. b: Know the life cycle of the Sun over its 9 billion year life. Friday 21 October 2011 Introduction: The Sun is the closest star to Earth and represents 99.1% of the mass of the entire solar system. The Sun formed over four and a half billion years ago, but it will keep shining for at least another five billion years. The Sun’s surface is called the photosphere. The temperature of the photosphere is about 6,000  centigrade. Its core is under its atmosphere. The temperature at the core, or very middle, of the Sun, is about 27 million  centigrade. The Sun is 109 times wider than Earth, and is 333,000 times heavier. That means if you put the Sun on a scale, you would need 333,000 objects that weigh as much as the Earth on the other side to make it balance. . P7.18 Our Sun

34. Key concepts P7.18 a Look at the photograph and information and answer all the questions: Name three types of radiation emitted by the Sun ? Although all electromagnetic waves travel through space from the Sun to Earth’s surface, sound doesn’t. Explain why this is a good thing ? The Sun is the star at the centre of the Solar System. It has a diameter of about 1,392,000 km, about 109 times that of Earth, and its mass is 330,000 times that of Earth. About three quarters of the Sun's mass consists of hydrogen, while the rest is mostly helium. Less than 2% consists of heavier elements, including oxygen, carbon and neon.

35. Look at the photograph and information and answer all the questions: Anatomy of the Sun Explain why the temperature cools as you move from the core of the Sun to its surface ? What element is the Sun made from and how could prove your answer ? The sun is made up of several layers, each layer has unique properties, which are vital to the sun's functions. The centre of the sun, the Core, is the only part of the sun that actually makes energy. The temperature in the Core is about 15,000,000 o C. The next layer of the sun is the Radioactive Zone, , the temperature here is about 5,000,000 o C. The layer that is next is called the Convection Zone, where solar material rises and falls due to heating and cooling. The temperature here reaches only 5,800 o C. The next section of the sun is called the Photosphere, which is actually what you see when you look at the sun. Key concepts P7.18 b

36. Look at the photograph and information and answer all the questions: Scientists believe that in the early Universe only hydrogen existed. Explain how other elements have formed ? Explain why and how all life will eventually end here on planet Earth ? The Sun has a lifespan of about 9 billion years and is already halfway through its life using up to 300,000 tonnes of hydrogen gas every second. Eventually, when all the hydrogen and helium is consumed, the Sun will rapidly expand forming a red giant that engulfs and scorches the first four planets including Earth. What follows then is its contraction, the formation of a white dwarf and then a neutron star. During this phase heavier elements are formed. The life cycle of an average star like our sun Stellar nebula Average star Red Giant Planetary nebula White Dwarf Neutron star 4.5 billion years B.C 4.5 billion years A.D 4.6 billion years A.D Key concepts P7.18 c Life cycle of an average star

37. P7.18 Plenary Lesson summary: core surface life heat Friday 21 October 2011 The mean distance of the Sun from the Earth is approximately 149.6 million kilometres, though the distance varies as the Earth moves from perihelion in January to aphelion in July. At this average distance, light travels from the Sun to Earth in about 8 minutes and 19 seconds. This means we never actually see the Sun where it is just where it was 8 mins and 19 seconds ago. How Science Works: Research into how we can determine the composition of stars like the Sun. Preparing for the next lesson: The Sun gives off ______ and light that the Earth needs to support _______.. The ____________ temperature of the Sun is about 6000 o C. The Sun is made out of 92% hydrogen, 7% helium and the rest is other low number gasses? The Sun’s ______ is the hottest part of its matter. Decide whether the following statements are true or false : False True 3: The Sun is half way through its life cycle ? False True 2: The gravitational pull of the Sun keeps Earth in its orbit? False True 1: The Sun is largely composed of chlorine and oxygen gases ?

39. Extension questions: 1: Name, in order, the colours of light in the visible part of the electromagnetic spectrum ? 2: Draw a diagram to show how a prism works ? 3: What's the difference between a emission and a absorption spectrum ? 4: What elements are present in the Earth’s atmosphere ? 5: What elements are present in the Sun’s atmosphere ? Know this: a: Know the composition and anatomy of stars like our Sun. b: Know what absorption and emission spectra show and how we have determined star composition. Friday 21 October 2011 Introduction: The light given out by a star can be analyzed using a prism to split the light up. When this was performed with sunlight in 1802 the resulting emission spectra showed black lines which means that some wavelengths were missing. These line are called Fraunhofer lines. These missing sections were analyzed closer and eventually it was discovered that certain elements in the stars atmosphere absorb certain wavelengths of light resulting in the fraunhofer lines. Each element will give a unique absorption spectrum by absorbing different parts of the visible light. Then were able to tell what was present in the stars atmosphere by analyzing the emission spectrum. P7.19 The composition of stars

40. Key concepts P7.19 a Look at the photograph and information and answer all the questions: What are the black bands of missing wavelengths called ? Explain why the emission spectra form deep space is different to the emission spectra of our own Sun ? When elements like sodium and magnesium burn with oxygen they give out light at certain colour or wavelengths. The spectrum form our own Sun and deep space are of course very different. The spectrum of sunlight above shows black band, these correspond to areas where elements in the suns atmosphere have absorbed these specific wavelengths. Light emission Our Sun Deep space Light spectrum from our Sun Light spectrum from deep space prism prism

41. Key concepts P7.19 b Look at the photograph and information and answer all the questions: Compare the emission spectra of our sun and hydrogen ? Explain why we know the Sun contains other elements in addition to hydrogen ? When the electrons in the atom are excited, (heated) the extra energy pushes the electrons to higher energy orbits. When the electrons fall back down and leave the excited state, energy is re-emitted in the form of a photon. The wavelength of the photon is determined by the difference in energy between the two states. These emitted photons form the element's emission spectrum . Light emission Our Sun Hydrogen Light spectrum from our Sun Light spectrum of hydrogen prism prism H 1 1

42. P7.19 Plenary Lesson summary: elements spectra lower stars Friday 21 October 2011 The Sun’s emission spectrum gives scientists a picture of the composition of the Sun,. Far form being simple it is very complex but it does give evidence that the Sun contains elements like hydrogen, helium and oxygen. How Science Works: Research into understand emission spectra and how atoms of different elements emit light by emitting photons with discreet energy levels. Preparing for the next lesson: Emission ______ can be used to determine to composition or ______ present in __ like our own Sun and even in deep space. Each element will give a unique emission spectra due to photons jumping form higher to ______ energy levels. Decide whether the following statements are true or false : False True 3: If a photon has been absorbed the resulting spectra will have an area of black ? False True 2: The emission spectra of hydrogen is different to the emission spectra of helium ? False True 1: In deep space, there is very little light emitted ?

44. Extension questions: 1: Define the term photon ? 2: Will light be emitted or absorbed if an electron jumps up an energy level ? 3: Will light be emitted or absorbed if an electron drop an energy level ? 4: Draw a diagram to represent absorption of light by an electron ? 5: Draw a diagram to represent emission of light by an electron ? Know this: a: Know why different elements have different absorption spectra b. Know that when an electrons drops from one energy to the next it emits a single photon (packet of energy) Friday 21 October 2011 Introduction: The absorption spectra of each element is unique. This is because all elements emit light in a different way. Light is emitted by an element when its electrons lose energy, as its lost in form of light energy. Light can also be absorbed by an atom. Electrons have certain set values of energy, if an electron drops to a lower energy level it emits a package of light called a photon. If an elecron jumps up an energy level it absorbs a photon of light and the resulting spectrum will show missing wavelengths of light. P7.20 Emission spectra

46. Assessment for learning...key concepts P7.20 b Look at the photograph and information and answer all the questions: Look at the emission spectra for a) hydrogen and b) helium what are the strongest colour and do you see these colours in spectra from the Sun ? Explain clearly why Fraunhofer lines (black line in the first spectra) are present on the emission spectrum of sunlight. ? If you analyse light from our sun (the solar spectrum) apart from some colours that are absorb by the Sun’s own atmosphere, you see a full spectrum of colours from red with a wavelength of 700 nm to violet with wavelength of about 400 nm. If you analyse light from pure elements like hydrogen, lithium, helium and sodium, you will set distinct emission spectra. By comparing the two you can begin to build a picture of the elements present as part of the Sun’s huge mass. Emission spectra and photons Sun’s emission spectra Hydrogen’s emission spectra Helium’s emission spectra Mercury’s emission spectra Uranium’s emission spectra

47. Key concepts P7.20 c Look at the photograph and information and answer all the questions: What would happen if the electron from the middle energy level jumped up to the upper energy level ? If the energy gap between energy levels is large would the photon emitted be high or low frequency ? Therefore, would it be a short or long wavelength ? In this simplified diagram above right three different energy levels are shown. Electrons can jump between these energy levels. The electron illustrated in green drops from the middle energy level to the lowest energy level. When this happens a photon of light is emitted. The energy of the photon is equal to the difference in the energy levels. = electron Emission spectra and photons Photon emitted Increasing energy

48. Key concepts P7.20 d Look at the photograph and information and answer all the questions: If an atom emitted mainly red light would it be emitting low or high energy photons ? Explain the link between the energy status of a photon and its wavelength ? In this simplified diagram above two electrons are shown. The electron shown in blue jumps form the highest to the middle energy level releasing a smaller amount of energy as a photon. The second electron shown in green jumps form the middle to lowest energy level. Here the jump is larger therefore the photon has more energy and a shorter wavelength. Photon emitted (high energy short wavelength) Increasing energy Photon emitted (low energy long wavelength) Colour of light from a high energy photons (blue) Colour of light from a low energy photons (red) Emission spectra and photons

49. P7.20 Plenary Lesson summary: absorb emits photon energy Friday 21 October 2011 In 1913, it was Neils Bohr who proposed that electrons revolves around the atom’s nucleus with a definite fixed energy, without emitting or absorbing energy. These energy levels are called Principal Quantum Levels. Level n = 1 is closest to the nucleus of the atom and of lowest energy. How Science Works: Research in atoms and their nuclei and the sub atomic particles know as electrons, protons and neutron. Also find out about the work of Geiger, Marsden and Rutherford. Preparing for the next lesson: If an electron drops an energy level it _______ a photon, which is a packet of _______ . If an electron jumps to a higher energy level it will ______ a photon. The amount of energy absorbed or emitted is calculated by the difference between the two energy levels. Decide whether the following statements are true or false : False True 3: If a photon has been absorbed the resulting spectra will have an area of black ? False True 2: Photons are packets of sound energy ? False True 1: Electrons can be made to move into higher and lower energy levels ?