Unit 1 Universal Physics

Transcription

1 Unit 1 Universal Physics (EdExcel)

2 Topic 1 Visible Light and the Solar System

3 Our understanding of the universe Up until the 16 th Century people believed that the Earth was the centre of the universe this is called the Geocentric model and I made a model of the universe based on it. Ptolemy, AD I published my On the revolutions of the celestial spheres just before my death and showed that the Earth and other planets orbit around the sun the Heliocentric model. Copernicus,

4 Evidence for the Heliocentric Model I helped develop the modern telescope and made measurements with it that proved that the Copernican model of the solar system was correct. Galileo, Jupiter and its moons, as seen through a telescope The orbits of these moons

5 Observing the Universe What are the advantages and disadvantages of each of these methods? A complex digital camera will be in here

6 An introduction to Waves A Wave is a movement of energy but NOT a transfer of matter

7 Wave definitions 1) Amplitude this is how high the wave is: 2) Wavelength (λ) this is the distance between two corresponding points on the wave and is measured in metres: 3) Frequency this is how many waves pass by every second and is measured in Hertz (Hz) 4) Speed this is how fast the wave travels and is measured in metres per second (m/s)

8 Transverse vs. longitudinal waves Transverse waves are when the displacement is at right angles to the direction of the wave. Displacement Direction Examples light, other EM waves, some seismic waves Displacement Direction Examples sound, some seismic waves Longitudinal waves are when the displacement is parallel to the direction of the wave

9 Refraction through a glass block: Wave slows down and bends towards the normal due to entering a more dense medium Wave slows down but is not bent, due to entering along the normal Wave speeds up and bends away from the normal due to entering a less dense medium

10

11 Refraction Refraction is when waves or slow down due to travelling in a different. A medium is something that waves will travel through. When a pen is placed in water it looks like this: In this case the light rays are slowed down by the water and are, causing the pen to look odd. The two mediums in this example are and. Words speed up, water, air, bent, medium

12 Lenses Lenses use the idea of refraction: When light enters a MORE DENSE medium it slows down A prism uses this idea to split light. This happens because purple light is refracted more than red light

13 Another example: The lens in the eye is used to focus what we see:

14 Converging and diverging lenses CONVERGING (Convex) Thickest at the centre DIVERGING (Concave) Thinnest at the centre

15 A distant object Ray diagrams for lenses 1 Focal length F The rays of light are refracted INWARDS and meet at the focus, F. The image formed is REAL in other words, it can be seen on a screen F The rays of light are refracted OUTWARDS. A VIRTUAL image is formed in other words, the image doesn t actually exist

16 Lenses in Telescopes Because stars are very far away, the rays of light from them enter a telescope effectively parallel: Objective lens (convex) Focal point Eyepiece lens The objective lens basically gathers as much light as possible from the distant star and focuses it inside the telescope. The eyepiece lens then magnifies this image into the eye.

17 Mirrors in Telescopes Astronomical telescopes tend to use large concave mirrors as well as a convex lens. This allows them to collect more light: Eyepiece lens Objective lens (convex) Flat mirror Concave mirror

18 The Wave Equation All E-M waves obey the Wave Equation: Wave speed (v) = frequency (f) x wavelength (λ) in m/s in Hz in m V f λ

19 Some example wave equation questions 1) A water wave has a frequency of 2Hz and a wavelength of 0.3m. How fast is it moving? 0.6m/s 2) A water wave travels through a pond with a speed of 1m/s and a frequency of 5Hz. What is the wavelength of the waves? 0.2m 3) The speed of sound is 330m/s (in air). When Dave hears this sound his ear vibrates 660 times a second. What was the wavelength of the sound? 0.5m 4) Purple light has a wavelength of around 6x10-7 m and a frequency of 5x10 14 Hz. What is the speed of purple light? 3x10 8 m/s

20 Distance, Speed and Time for waves D Speed = distance (in metres) time (in seconds) S T 1) A water wave travels 200 metres in 40 seconds. What is its speed? 2) Another wave covers 2km in 1,000 seconds. What is its speed? 3) Sound travels at around 330m/s. How long does it take to travel one mile (roughly 1,600m)? 4) Light travels at a speed of 300,000,000m/s. How long would it take to travel around the world if the diameter at the equator is around 40,000km?

21 Topic 2 The Electromagnetic Specturm

22 The Visible Spectrum In the 17 th Century I did lots of work on light and wrote about how visible light was made of the colours of the spectrum. Isaac Newton, Wilhelm Ritter, I accidentally discovered that, if you put a thermometer here, it gets hot. I discovered Infra Red radiation!! I then discovered ultra violet by observing how salts made from silver were lightened by something just beyond violet light. William Herschel,

23 Electromagnetic Radiation E-M radiation is basically a movement of energy in the form of a wave. Some examples:

24 The Electromagnetic Spectrum Each type of radiation shown in the electromagnetic spectrum has a different wavelength and a different frequency: High frequency, wavelength Low frequency, (high) wavelength Gamma rays X-rays Ultra violet Visible light Infra red Microwaves Radio/TV γ Each of these waves travels at the same speed through a (300,000,000m/s), and different wavelengths are absorbed by different surfaces (e.g. infra red is absorbed very well by surfaces). They all travel as waves. The more dangerous waves are at the high end of the spectrum. Words black, transverse, long, short, vacuum, frequency

25 The Electromagnetic Spectrum Type of radiation Uses Dangers Gamma rays X rays Treating cancer, sterilisation Medical, airport scanners Cell mutation Cell mutation Ultra violet Visible light Infra red Microwaves TV/radio Sun beds, security Seeing things, photos Remote controls, heat transfer, optical fibres Satellites, phones Communications Skin cancer None (unless you look at the sun) Skin burns Heating of cells Very few

26 Introduction to Radioactivity Some substances are classed as radioactive this means that they are unstable and continuously give out radiation: Radiation The nucleus is more stable after emitting some radiation this is called radioactive decay. Radiation like this can be either alpha, beta or gamma radiation.

27 Ionisation Radiation is dangerous because it ionises atoms in other words, it turns them into ions by knocking off electrons: Ionising radiation is emitted by radioactive sources all the time. Ionisation transfers energy to cells in living tissue, causing them to mutate, usually causing cancer.

28 Topic 3 Waves and the Universe

29 Space: An introduction OUR SUN is one of millions of stars that orbit the centre of THE UNIVERSE, made up of everything!! THE MILKY WAY, which is one of a billion galaxies that orbit AND move away from the centre of

30 How our Earth and the Sun compare to others

31

32

33

34

35 Distances in space The Sun, our closest star, is 1.6x10-5 light years away from us. The next closest star, Proxima Centauri (4.2 light years away) The centre of our galaxy, the Milky Way, is around 26,000 light years away. The Andromeda Galaxy (our closest galaxy) approximately 2.5 million light years away

36 Observing the Universe Consider different types of telescope: Radio telescopes Space-based telescopes The original telescopes were used purely for visible light. These days, telescopes pick up a wide range of waves. Some examples...

37 Hubble Space Telescope (HST) Launched in 1990, due to finish operating in 2010 Takes images in the visible light, ultra-violet and near infra red regions Orbits the Earth every 97 minutes

38 The number of known astronomical bodies was increased by 70% due to infra red observations Infra Red Astronomical Satellite (IRAS) Surveys infra red patterns in space Launched in 1983 and operated for 11 months

39 Cosmic Background Explorer (COBE) Operated from 1989 to 1993 Detected small ripples in the Cosmic Microwave Background Radiation (CMBR) reaching the Earth

40 Life on Other Planets Research task Is it likely that other planets in our solar system could have life? Explain your answer. Extend your inquiry to other solar systems what criteria must be met in order for a planet to potentially have life on it?

41 Searching for Aliens Humans have been searching for me for over 50 years. Here are some of the methods they use: Space probes SETI The Search for Extra Terrestrial Intelligence Since 1960 a group of astronomers have collectively been sending out EM signals hoping that someone will send one back! The Voyager 1 probe, still in operation after over 33 years and still sending signals back to Earth. Soil samples Soil samples from the moon and, in recent years, from Mars have been sampled. What are the advantages and disadvantages of each of these methods?

42 How modern telescopes have helped Due to technological advances in telescopes our knowledge of the universe has been expanded. Some examples: 1) In 1610 I used a telescope to determine the existence of a galaxy around us the Milky Way due to better magnifications in my telescope. Galileo 2) Some stars don t emit visible light, so they are seen by taking infra red photos and then applying false colour : 3) The Hubble Space Telescope has been able to take measurements to more accurately determine the age of the universe around 14 billion years.

43 Making a simple spectrometer Slit

44 Observing the Universe Consider different types of telescope: Ground-based telescopes Space-based telescopes What are the advantages and disadvantages of each?

45 Benefits of observing above the atmosphere Clearly, ground-based telescopes are a problem because of a number of things: The amount of light absorbed by the atmosphere Bad weather Light is refracted, diffracted and scattered by the atmosphere (causing stars to twinkle ) Ground-based telescopes

46 The Life Cycle of a Star

47 Stage 1: Nebulae A nebulae is a collection of dust, gas and rock. Some examples of nebulae

48 Dark nebula

49 Emission nebula

50 Reflection nebula

51 Planetary nebula (This nebula is smaller and will only form a planet)

52 Stage 2: Protostar Gravity will slowly pull these particles together As they move inwards their gravitational potential energy is converted into heat and a PROTOSTAR is formed

53 Stage 3: Main Sequence In a main sequence star the forces of attraction pulling the particles inwards are by radiation pressure acting outwards due to the huge inside the star. Stars are basically reactors that use as a fuel. During its main sequence a star will release energy by converting hydrogen and helium (light elements) into elements. Our sun is an example of a main sequence star it s in the middle of a 10 billion year life span Words heavier, balanced, hydrogen, nuclear, temperatures

54 Stage 4: Red Giant Eventually the hydrogen and helium will run out. When this happens the star will become colder and redder and start to swell If the star is relatively small (like our sun) the star will become a RED GIANT If the star is big (at least 4 times the size of our sun) it will become a RED SUPERGIANT

55 Stage 5: The Death What happens at this point depends on the size of the star 1) For SMALL stars the red giant will collapse under its own gravity and form a very dense white dwarf: Red giant White dwarf Black dwarf

56 2) If the star was a RED SUPERGIANT it will shrink and then EXPLODE, releasing massive amounts of energy, dust and gas. This explosion is called a SUPERNOVA Before After

57 The dust and gas on the outside of the supernova are thrown away by the explosion and the remaining core turns into a NEUTRON STAR. If the star is big enough it could become a BLACK HOLE.

58 Stage 6: Second generation stars The dust and gas thrown out by a supernova can be used to form a new star Our sun is believed to be a star this is because it contains some elements along with hydrogen and. These heavier elements would have been the products of a previous star that have been thrown out by a. These heavier elements are also found on planets, indicating that they might have been made from remains of previous as well. Words helium, heavier, second generation, stars, supernova

59 This theory states that the universe started off with an explosion and everything has been moving away ever since. There are two main pieces of evidence for this: background microwave radiation and red shift. The formation of the universe There are two main theories about how the universe started: The Steady State theory This theory states that the universe has always existed as it does now and hasn t changed. The trouble is that the night sky would be completely lit up because of the billions of stars, but it s not, so The Big Bang theory

60 Evidence about the origins of the universe

61 Microwaves When the Big Bang happened microwaves were produced and these are still reaching us now. They can sometimes be seen as TV interference.

62 Red Shift explained Source of light Spectra

63 If you pass the light through a gas something different is seen helium Some wavelengths of light are absorbed by the gas an absorption spectrum.

64 If the light source is moving away the absorption spectra look a little different Before helium After

65 The absorption lines have all been shifted towards the longer wavelength end (red end) This is called red shift. The faster the light source moves the further its light will be shifted Before After A similar effect happens with sound this is called The Doppler Effect Hear Doppler Effect

66 Red Shift simplified Basically, if I walk towards you I ll look slightly more blue. Then, if I walk away from you, I ll look slightly more red!! Let s try it

67

68

69 Light from different stars and from the edge of the universe also shows this red-shift. This suggests that everything in the universe is moving away from a single point. This is the BIG BANG theory

70 Red shift summary Light from other galaxies has a longer than expected. This shows that these galaxies are moving from us very quickly. This effect is seen to a greater extent in galaxies that are away from us. This indicates that the further away the galaxy is, the it is moving. This evidence seems to suggest that everything in the universe is moving away from a single point, and that this process started around 14 years ago. This is the Theory. Further evidence of this theory is Cosmic Microwave Background Radiation (CMBR) this radiation comes from the Big Bang and fills the. Words to use faster, away, universe, big bang, billion, wavelength, further

71 Big Bang Theory vs Steady State Some scientists have explained that red shift can actually be used to support the Big Bang Theory this explanation is based around the rates of expansion and contraction of different galaxies. If our neighbouring galaxy is expanding at a different rate to the Milky Way then it will appear red or blue-shifted. However, the discovery of CMBR was the final nail in the coffin for the Steady State theory. So, Mr President, the Big Bang theory is now the widely accepted theory of how the universe began. Stephen Hawking,