Electromagnetic Waves

Transcription

1 Big Bang Theory

2 OUTLINE First 25 minutes of the video Notes on waves, Doppler effect, and red/blue shift Mini lab on spectrums and how they are used to understand red and blue shift Mini lab on the expanding universe Video Understanding the Big Bang and Atom formation

3 scienceaid.co.uk

4 Electromagnetic Waves (short) (1:18, explained) Transverse wave made up of electrical and magnetic energy It is produced when the electric and magnetic fields switch back and forth (vibrating) causing a disturbance that travels through space as a wave. This wave carries energy and information from one part of the universe to another, which is called electromagnetic radiation. Our instruments pick up these electromagnetic waves and change them into vibrating tunes/static They travel at the speed of light: 299, km/s in a vacuum

5 Electromagnetic Spectrum All electromagnetic waves travel at the same speed in a vacuum, but they have different wavelengths and different frequencies (Pasachoff 75). An electromagnetic spectrum is the complete range of electromagnetic waves placed in order of increasing frequency (Pasachoff 75). Radio waves, Infrared rays, Visible light, ultraviolet rays, X-rays, and gamma rays.

6 Electromagnetic Spectrum Radio Waves Longest wavelength and lowest frequencies Broadcast waves and microwaves Infrared Rays Wavelengths shorter than radio waves The invisible heat you feel

7 Visible Light You can see these waves The longest wavelengths and lower frequencies (and lowest energies) appear in the red and the shortest wavelengths and higher frequencies (and higher energies) appear in the violet/blue. Violet Blue Green Yellow Orange Red

8 Ultraviolet rays Shorter wavelengths and higher frequencies than visible light They carry more energy than visible light Pros: killing bacteria and providing vitamin D Cons: to much exposure causes skin cancer, can damage your eyes, and burn your skin X-Rays: Shorter wavelengths and higher frequencies than ultraviolet rays, thus can carry more energy Can go through most matter, except dense matter like bones Gamma Rays: Have the shortest wavelength and highest frequencies, thus has the greatest amount of energy Great penetrating ability Pros: use to kill cancer cells inside the body, use to help see inside the body Cons: produced by nuclear reactions and can be harmful (even deadly if exposed to too much).

9 Sound Waves and Stars: The Doppler Effect blue blue red red

10 Spectral Line Analysis Activity

11 Spectrographs /color/spectra/ Spectrum Tubes Instrument to separate white light into the bands of color This is a spectrum from our sun. The dark lines are where different elements have absorbed different frequencies of light. Each element has its own spectrum, kind of like a finger print. Scientists use spectrographs to determine what elements other stars are made of.

12 Spectrums A, B and C are from identical stars within our galaxy. Spectrum A represents a possible spectrum of a star not moving toward or away from Earth. Spectrums B and C show stars in motion with respect to an observer on Earth. Compare the three spectrums and answer the following questions:

13 Spectrographs Weber Online Spectrograph Practice

14 HUBBLE S DISCOVERY Just as the light from a single star can be used to make a stellar spectrum, scientists can also use the light given off by an entire galaxy to create the spectrum for that galaxy (Holt 793). In the 1920s, Hubble found that the spectra of galaxies, except a few near our own, were all shifted towards the red end of the spectrum. By measuring the redshift he was able to determine the speed at which the galaxies were moving away from us. Galaxies farthest away show the greatest redshift and therefore the greatest speed. This evidence pointed to the fact that our universe was expanding.

15 Most galaxies are red-shifted (moving away from us) today. Let s rewind the clock of time. Using the information and data from what you have learned, what can be inferred about the origin of the universe?

16 Balloon Lab Question: How is the universe expanding? Vocabulary words Independent variable: a factor that is changed on purpose; also called manipulated variable Dependent variable: a factor that is observed or measured in response to a change in the independent variable; also called responding variable

17 BIG BANG SUMMARY NOTES

18 BIG BANG THEORY The Big Bang Theory claims that the universe has expanded from a very dense, very hot state that existed at some time in the past. Evidence to support Studies of red-shifts of distant galaxies show that the universe is expanding. Cosmic Background radiation (left over energy/heat) Abundance of Hydrogen and Helium

19 Big Bang Model Running the expansion backward allows us to calculate the temperature and density of the universe during its earliest moments. The known laws of physics can be used to determine the behavior of matter and energy at these temperatures and densities. The model is then used to make predictions that can be compared to observations. The only elements in the early universe were hydrogen and helium (and a tiny amount of lithium). The hydrogen-helium mass ratio was about 75-25%. Microwaves with an energy corresponding to a temperature of about 3 K will be found everywhere in space. From Earth they will be seen across the entire sky.

20 TEMPERATURE Summary: It was extremely hot and then started to cool slowly until it is now extremely cold. Temperature played a crucial role in the formation of matter. Time One million of a second 10-thousand of a second 10 th of a second Cooling A second Temperature K (ten trillion Kelvin) a lot of energy Or 179,999,999,999, F K (one trillion Kelvin) Or 17,999,999,999, F Cooling 100 seconds 10 9 K or 1, 799,999, F 10 minutes cooling 380,000 years 3,000 K or 4, F Now 3 degree above absolute zero or 3 K or F

21 BIG BANG TIME LINE Formation of matter

22 Where did matter in the universe come from? E = mc 2 Mass is just condensed energy Energy mass Albert Einstein A particle antiparticle pair can be created if the available energy equals the mass of both particles times the speed of light squared A very BIG number!

23 START Too hot for any matter to form, only pure energy

24 ABOUT A MILLIONTH OF A SECOND K (ten trillion Kelvin) or 179,999,999,999, F Protons, anti-protons, neutrons and anti-neutrons begin to form because of cooler temperatures As a proton or neutron collides with its anti-particle they annihilate and are converted to energy in the form of photons Photons are light particles neutron proton anti-proton anti-neutron

25 About one ten-thousandth of a second... It is no longer hot enough to produce protons and antiprotons (or neutrons and anti-neutrons) spontaneously from pure energy to replace those that annihilate each other. Almost all particles and antiparticles annihilate and produce gamma ray photons. proton anti-proton Photons are constantly scattered by free particles with an electric charge like electrons or protons These photons increase in wavelength as the universe expands and will eventually become the majority of photons that make up the cosmic background radiation

26 ONE TEN-THOUSANDTH OF A SECOND... CONTINUED a billion photons for every proton or neutron High energy collisions between protons, neutrons and other particles like electrons can transform one particle into another. maintains equal numbers of protons and neutrons... p + + e n + e n + e + p + + e

27 About a tenth of a second... As the temperature (and available energy) drops, transformation to protons is favored over neutrons About one second Transformation reactions can no longer occur. Neutrons begin to decay into protons n p + + e + e

28 ABOUT 100 SECONDS Neutron decay results in a 1:7 ratio of neutrons to protons. Universe is now cool enough for protons and neutrons to bind together. This is called fusion. proton (hydrogen nucleus) deuterium neutron tritium helium This process creates new, heavier atomic nuclei and is called nucleosynthesis.

29 AT THE BEGINNING OF NUCLEOSYNTHESIS protons 2 neutrons At the end of nucleosynthesis hydrogen nuclei 1 helium nucleus Atomic mass = 12 Atomic mass = 4 Mass ratio 75% 25%

30 About 10 minutes... the end of big bang nucleosynthesis Very little happened in nucleosynthesis for a long time as temperature and density are too low for fusion.

31 ABOUT 380,000 YEARS Temperature drops to 3000 K Universe is cool enough for electrons to bind with nuclei and form stable atoms H He With most electrons now bound in atoms, photons can travel large distances without being scattered by free electrons. Photons now travel in all directions, resulting in what is called the cosmic background radiation.

32 NOW With continued expansion, temperature drops to about 3 K (Three degrees above absolute zero) Photons that make up the cosmic background radiation are now microwaves most of these photons were produced by the particle antiparticle annihilation at about one ten-thousandth of a second