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Areas of Knowledge SCIENCE

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Science For thousands of years humans have had a miserable existence. A short life characterised by cold, hunger, disfiguring diseases and eventually a premature and painful death. In the last 100 years or so we have largely be spared this. People suffer less and live longer. In general people are better educated and can now live meaningful lives. This is not a miracle – it is due to Science. Simon Porter

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What is a scientist? Draw and/or describe your typical scientist

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Google thinks they look like this :

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And can be defined like this: A person who has studied science, especially one who is active in a particular field of investigation. a person who uses observation, experimentation and theory to learn about a subject (Biologists, physicists, chemists, geologists and astronomers are all scientists.) education.jlab.org/beamsactivity/6thgrade/vocabulary/index.html education.jlab.org/beamsactivity/6thgrade/vocabulary/index.html a person that knows a great deal about a branch of science. An ornithologist is a scientist that specializes in the study of birds. a person with advanced knowledge of one or more sciences wordnet.princeton.edu/perl/webwn wordnet.princeton.edu/perl/webwn What features did you identify?

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What are the ideal characteristics of a scientist? Collaborative Observant Creative Open-minded Risk-taking Methodical Analytical ?? How about being a believer? Being perseverant? Being ethical?

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CSI Series 1 episode 10 Whilst watching this episode – fill in the sheet.

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Learn the Truth card game Each group offers a card, which the Mr Porter takes or rejects according to an unknown rule Work out what the rule is to win a point for your team No random guessing – your group may only propose a theory once it has been discussed and agreed in the group. You can only suggest the answer when it is your turn

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Lets go!

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The first three rules were: 1.Red, black, red, black, red… 2.Spade, heart, club, diamond, spade, heart, club, diamond… 3.Odd, even, Odd, even, Odd, even… It may have been hard to distinguish the first two patterns, because 2 is a specialised form of 1. They look the same, & once stuck in a theory you may have succumbed to confirmation bias What was needed to distinguish them? Experimenting, esp: falsification

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The processes you are using: Observing Reasoning Intuiting Decision making Teamwork Cooperating and competing

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Pattern spotting Guessing the rule Testing the rule = Empirical observation Forming an inductive, reasoned hypothesis Testing by falsification Which is the most important part of the process? Your processes refined:

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Lets try some more complex patterns

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Try these patterns: 4. P, not P, P, not P, P, not P… 5. Card given by boy, girl, boy, girl… 6. Accepted if given from left hand, right hand, left hand… 7. Accepted if offered with a bribe… Simple rules, but hard to discern because: You were looking for the wrong thing: you looked in the cards, not in the circumstances. You made assumptions without realising. Paradigms were not the whole story.

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What did this have to do with ToK? The teacher was Nature You were scientists, trying to understand Natures workings & rules You cooperated & competed in order to succeed You observed You hypothesised, by using inductive reasoning & intuition You tested, most successfully by falsification You modified your theories Simple appearances hid complex patterns, and vice versa Your paradigms got in the way of knowledge Just like SCIENCE and scientists!

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What is the scientific method? How do scientists gain their knowledge?

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Remember the characteristics of scientists Collaborative Observant Creative Open-minded Risk-taking Methodical Analytical ??

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Pattern spotting Guessing the rule Testing the rule = Empirical observation Forming an inductive, reasoned hypothesis Testing by falsification Remember the processes used in the card game

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Key elements must be: observation of empirical and measurable evidence, experimentation (esp falsification, the process by which we eliminate failures and falsehoods ), and Logical, rational and coherent theoretical explanations Draw and label a diagram or flow-chart of the model scientific method

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How does your model compare with this one? Experimental data or observation Inductive hypothesis Prediction and experimental testing Theory confirmed and published as knowledge Theory is falsified and discarded What are the problems or issues with this model?

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Paradigms and perception problems with observation (see next slide) Subjectivity rather than objectivity in observations Confirmation bias (Millikans oil drop – following slide)) What are the problems or issues with this model? What is the essential component of the scientific method?

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The extra chromosomes! The Bizarre Case of Chromosomes that Never Was by Robert Mathews is a fascinating article that explores the human nature of conformity. In 1932, the American zoologist Theophilus Painter, published a study where he claimed that they are 24 pairs of chromosomes in the human body. Painter did so fully confident in his findings. As other scientist repeated Painters study they claimed to also find 24 pairs of chromosomes. However there were a few scientists who claimed to see as few as 19 and others 23. These scientists then thought their findings were just wrong because they knew that there was went to be 24. That is until 1956, when scientist finally discovered a way to place cells on microscope slides, which helped separate the chromosomes clearly. When scientists did this they found that there was in fact only 23 chromosomes in the human body. Researchers even went back to textbooks and looked at the photographs of chromosomes. They found that the photograph clearly showed 23 pairs of chromosomes, however the caption stated that there were 24 pairs.

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Charge on an electron Robert Millikan performed a ground breaking experiment between 1900 and 1913 to measure the change on an electron. There is some controversy over the use of selectivity in Millikan's results raised by the historian Gerald Holton. Holton (1978) pointed out that Millikan disregarded a large set of the oil drops gained in his experiments without apparent reason.

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models of scientific change: Karl Popper Each theory builds progressively on the theories preceding it 3 2 1

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Paradigms encompass some parts of previous theories, but reject other parts models of scientific change: Thomas Kuhn

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Theories have little to do with previous theories, and are incoherent or inconsistent. models of scientific change: Paul Feyerabend It could be argued that the scientific method itself has been developed over time, scientifically!

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An example – quantum physics

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Atomic spectra When a gas is heated to a high temperature, or if an electric current is passed through the gas, it begins to glow. cathodeanode electric current Light emitted Low pressure gas

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Emission spectrum If we look at the light emitted (using a spectroscope) we see a series of sharp lines of different colours. This is called an emission spectrum.

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Absorption Spectrum Similarly, if light is shone through a cold gas, there are sharp dark lines in exactly the same place the bright lines appeared in the emission spectrum. Some wavelengths missing! Light source gas

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Why? Scientists had known about these lines since the 19 th century, and they had been used to identify elements (including helium in the sun), but scientists could not explain them.

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Rutherford At the start of the 20 th century, Rutherford viewed the atom much like a solar system, with electrons orbiting the nucleus.

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Rutherford However, under classical physics, the accelerating electrons (centripetal acceleration) should constantly have been losing energy by radiation (this obviously doesnt happen). Radiating energy

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Niels Bohr In 1913, a Danish physicist called Niels Bohr realised that the secret of atomic structure lay in its discreteness, that energy could only be absorbed or emitted at certain values. At school they called me Bohr the Bore!

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The Bohr Model We say that the energy of the electron (and thus the atom) can exist in a number of states n=1, n=2, n=3 etc. (Similar to the shells or electron orbitals that chemists talk about!) n = 1 n = 3 n = 2

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The Bohr Model We can show the energy levels on a diagram n = 1 (the ground state) n = 2 n = 3 n = 4 n = 5 High energy n levels are very close to each other Energy eV Electron cant have less energy than this

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Atomic transitions If an electron is a level above the ground state, it can make a transition to a lower state. Thus an atom in state n = 2 can go to n = 1 (an electron jumps from orbit n = 2 to n = 1) n = 1 (the ground state) n = 2 n = 3 n = 4 n = Energy eV 0 electron Wheeee!

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Atomic transitions Every time an electron makes a transition, a single photon of light is emitted ( a little packet of light energy) n = 1 (the ground state) n = 2 n = 3 n = 4 n = Energy eV 0 electron

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Atomic transitions The energy of the photon is equal to the difference in energy (ΔE) between the two states. n = 1 (the ground state) n = 2 n = 3 n = 4 n = Energy eV 0 electron ΔEΔE

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The Lyman Series Transitions down to the n = 1 state give a series of spectral lines in the UV region called the Lyman series. n = 1 (the ground state) n = 2 n = 3 n = 4 n = Energy eV 0 Lyman series of spectral lines (UV)

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The Balmer Series Transitions down to the n = 2 state give a series of spectral lines in the visible region called the Balmer series. n = 1 (the ground state) n = 2 n = 3 n = 4 n = Energy eV 0 UV Balmer series of spectral lines (visible)

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The Pashen Series Transitions down to the n = 3 state give a series of spectral lines in the infra-red region called the Pashen series. n = 1 (the ground state) n = 2 n = 3 n = 4 n = Energy eV 0 UV visible Pashen series (IR)

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Emission Spectrum of Hydrogen Which is the emission spectrum and which is the absorption spectrum? The emission and absorption spectrum of hydrogen is thus predicted to contain a line spectrum at very specific wavelengths, a fact verified by experiment.

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Limitations of the Bohr Model 1.Can only treat atoms or ions with one electron 2.Does not predict the intensities of the spectral lines 3.Inconsistent with the uncertainty principle (see later!) 4.Does not predict the observed splitting of the spectral lines

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Light as particles and waves In 1905 Einstein showed that the photoelectric effect could be understood if light were thought of as a stream of particles (photons). This seemed to contradict some other experiments that shows light travels as waves. I got my Nobel prize for that.

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Louis de Broglie (in 1923) If light can behave both as a wave and a particle, I wonder if a particle can also behave as a wave?

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Louis de Broglie Ill try messing around with some of Einsteins formulae and see what I can come up with.

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I can imagine a photon of light. If it had a mass of m p, then its momentum would be given by p = m p c where c is the speed of light.

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Now Einstein has a lovely formula that he discovered linking mass with energy (E = mc 2 ) and he also used Plancks formula E = hf. What if I put them equal to each other? mc 2 = hf

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So for my photon m p = hf/c 2 So if p = m p c = hf/c

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p = m p c = hf/c Now using the wave equation, c = fλ (f = c/λ) So m p c = hc/λc = h/λ λ = h p

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So youre saying that a particle of momentum p has a wavelength equal to Plancks constant divided by p?! Yes! λ = h/p It will be known as the de Broglie wavelength of the particle

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Confirmation of de Broglies ideas De Broglie didnt have to wait long for his idea to be shown to be correct. In fact in 1929 I received a Nobel prize for my prediction of the wave nature of the electron.

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Confirmation of de Broglie De Broglies hypothesis was confirmed independently by Clinton Davisson (USA) and George Thomson (UK) in 1927 Ironically my Dad (J.J.) had won a Nobel prize for demonstrating that the electron was a particle!

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The electron in a box model! Hi! Im Erica the electron

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The electron in a box model! Imagine an electron is confined within an atom of diameter L. L

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The electron in a box model! According to de Broglie, it has an associated wavelength λ = h/p L

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L The electron in a box model! Imagine then the electron wave forming a stationary wave in the atom.

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L The electron in a box model! Therefore we have a stationary wave with nodes at x = 0 and at x = L (boundary conditions)

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The electron in a box model! The wavelength therefore of any stationary wave must be λ = 2L/n where n is an integer. L

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The electron in a box model! The momentum of the electron is thus P = h/λ = h/2L/n = nh/2L

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The electron in a box model! The kinetic energy is thus = p 2 /2m = (nh/2L) 2 /2m = n 2 h 2 /8mL 2

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The electron in a box model! E k = n 2 h 2 /8mL 2 The energy depends on n 2 L

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Energy states This can be thought of like the allowed frequencies of a standing wave on a string (but this is a crude analogy).

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Erwin Schrödinger The many problems with the Bohr model were corrected by Erwin Schrödinger, an Austrian physicist. /watch?v=IOYyCHG WJq4&feature=relate d I like cats! d 2 Ψ/dx 2 = -8π 2 m(E – V)Ψ/h 2 The Schrödinger equation

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Erwin Schrödinger Schrödinger introduced the wave function, a function of position and time whose absolute value squared is related to the probability of finding an electron near a specific point in space and time. I dont believe that God plays dice!

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Erwin Schrödinger In this theory, the electron can be thought of as being spread out over a large volume and there are places where it is more likely to be found than others! This can be thought of as an electron cloud. Rubbish!

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Wave function Ψ = (2/L)½(πnx/L) where n is the state, x is the probability of finding the electron and L is the length of the orbital. From this we also get the energy to be E K = h 2 n 2 /8m e L 2

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Beware! This wave function is only a mathematical model that fits very well. It also links well with the idea of wave particle duality (electron as wave and particle). But it is only one mathematical model of the atom. Other more elegant mathematical models exist that dont refer to waves, but physicists like using the wave model because they are familiar with waves and their equations. We stick with what we are familiar!. Im used to the idea of waves, so I like using Schrödingers model

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Heisenberg Uncertainty Principle wPlE8&feature=relmfuhttp://www.youtube.com/watch?v=gS1dpo wPlE8&feature=relmfu

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Heisenberg Uncertainty Principle It is not possible to measure simultaneously the position AND momentum of a particle with absolute precision. ΔxΔp h/4π Also ΔEΔt h/4π

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A few videos to try and explain! v2Ym8&feature=endscreen&NR=1 The great Richard Feynman

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What does wrong mean? Newton versus Einstein

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Newtons law of gravity Newton said that anything in the Universe that has mass, has a property of attraction for any other mass in the Universe. This attraction is a force that wants to pull masses together. The size of the pull depends on how big the masses are, and how far apart they are.

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Newtons law of motion Basically, Newtons Laws of Motion say three things. To change momentum a force must be applied. The applied force is proportional to the change in momentum. Every force that is applied produces a resisting force, equal and in opposite direction to the applied force. It is possible to create a mathematical formula from the Second Law: F=ma where F is the applied Force, m is the mass being accelerated and a is the acceleration.

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Using Newtons laws NASA uses them – for all the spacecraft that have visited the outer reaches of the Solar System. The calculated trajectories are highly accurate in every case. One Voyager even passed through a small gap in Saturn's rings, without incident. And that was using Newton's laws of motion over a distance of more than 1,280,000,000 km (800,000,000 miles).

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Einstein and Newton Einstein showed that Newtons laws break down when velocities approached that of light. Einstein showed that Newton's Law of Gravitation was also only approximately correct, breaking down in the presence of very strong gravitational fields.

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Was Newton Wrong? Newton's laws are wrong in certain circumstances. Einstein took the ideas and made them better. We should probably describe Newtons ideas as limited. Are theories being put forward today that could prove Einstein Wrong?

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