PhysicsLAB: Parallel Reading - In Search of Giants

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These videos are sponsored by the Science and Technology Facilities Council of the United Kingdom [link]. They were originally completed by Dr. Brian Cox in 2008 and are now currently (2025) hosted on YouTube, SciTechUK. There are 15 episodes [link].

1. Who discovered the electron in 1897?

2. Since atoms were normally neutral, and did not carry large amounts of negative charged, this scientist formulated a "picture" of the atom called the ______ ______ Model where positive and negative charges filled spheres with diameters on the order of 10^-9 meters.

3. Who discovered X-rays in 1895?

Three types of Uranium Glass
By Łukasz Karolewski (Own work)
[CC BY-SA 4.0 (http://creativecommons.org/licenses/by-sa/4.0)], via Wikimedia Commons

4. Becquerel accidently discovered ______ on March 1, 1896, when he noticed that some unexposed photographic films which he had stored near some uranium salts had become cloudy. Further studies showed that x-rays had not be the cause of the reaction. In 1903 he shared the Nobel Prize in Physics with Pierre and Marie Curie.

5. In 1898 Rutherford confirmed that there who two types of rays being emitted by the uranium salts: ______ and ______.

6. Later Rutherford discovered that these "rays" were actually ______. He was awarded the 1908 Nobel Prize in Chemistry for his "investigations into the disintegration of elements and their chemistry."

7. Rutherford first noticed alpha scattering when the normally sharp image positions of a beam of alpha particles reaching a photographic film were blurred when the particles first passed through a sheet of ______.

Initially the experiments conducted by Rutherford and Geiger only revealed scattering of one or two degrees. To continue their work, Geiger asked Rutherford for a relevant task to assign to Marsden, his research student. Rutherford suggested that Marsden look for large-angle scattering. Almost immediately Marsden found evidence of some alpha particles bouncing straight back after striking the gold foil. Such behavior would have been impossible in Thomson's model of the atom.

8. Rutherford's conclusion was that "most of the mass and charge had to be concentrated in a very small central body", which is now call the ______. It wasn't until 1913 that Rutherford definitively stated that this central body had to carry a positive charge.

9. Rutherford calculated that central body had a radius of only ______. He also stated that the majority of the atom was ______ ______ which explained why most of the alpha particles passed through the film without being deflected.

10. In 1915, ______ ______ postulated that the orbits of the electrons could only exist at certain distances, or energy levels, from each atom's centrally charged body.

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Molecular Expressions Animation: The Rutherford Experiment

Image courtesy of Michael W. Davidson and the Florida State University System.
Accessed on 21 August 2016

11. When the slit through which the alpha particles reached the 0.00004-cm thick gold foil was narrow (0.9 x 10^-9 meters) the majority of the alpha particles travelled with little or no deflection through the foil and struck the zinc-sulfide film. This behavior supported ______ model that positive and negative charges were spread evenly within the atom and only the electrostatic Coulomb forces (attracting and repelling similar and different + and - charges) were acting on the high speed alpha particles as they passed through the film.

12. When the slit was opened much further Geiger and Marsden noticed that a small percentage of the high velocity, massive alpha particles were deflected through significantly large angles. Alpha particles were known to be roughly ______ times more massive than electrons. This backscattering of alpha particles could not happen unless there was a concentrated central object holding all of the positive charge and mass of the atom. Most of an atom's spatial volume had to be created by the orbiting electrons. NOTE: it wasn't until 1920 that Rutherford determined that the positive charges were held by another subatomic particle, the proton.

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Atoms and the Periodic Table (#1)

13. In the 19th century (1800's) scientists thought that everything on earth was made up of only 80 elements which were arranged in a periodic table by ______ ______. They thought that these elements were made up of indivisible spheres called atoms. Because there were 80 different elements, did that mean that there were 80 different types of atoms? Or were atoms composed of even smaller objects?

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Discovery of the Electron (#2)

14. In 1986 ______ received an apparatus that allowed for particles to be accelerated and then bent so that the beam's position could be observed.

15. Prior to his discovery, scientists thought that the lightest known particle was the hydrogen atom but his electron had a mass of roughly 1/2000ths of that of Hydrogen. He had discovered the first ______ particle.

16. Electrons are called ______ particles because they cannot be sub-divided into smaller objects.

17. Describe how Thomson imagined electrons fitting into an atom.

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The Discovery of the Atomic Nucleus (#3)

18. Dr. Cox states that in his opinion Rutherford was the first particle physicist since he used beams of ______ to explore the structure of matter.

19. Rutherford's beams of particles came from the decay of ______ particles.

20. Rutherford replaced Thomson's model of an atom with one where the atom resembled a ______ ______, with all the mass concentrated in the center with the electrons orbiting like the planets around the Sun.

21. By 1932 Rutherford and ______ had discovered that there were two nuclear (subatomic) particles: protons and neutrons.

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Millikan's Oil Drop

By tracking the behavior of oil drops of a known density, Millikan and Fletcher were able to calculate the ratio of mass per unit charge for a multitude of drops that reached terminal velocity. Subsequently they could calculate the radius of a oil droplet based its terminal velocity and the equations for the required air resistance it should encounter while falling. Knowing the sphere's radius allowed them to calculate its volume and determine a drop's mass.

22. They reached the conclusion that the charges carried by all of the oil droplets had to be a ______ of the value 1.592 x 10^-19 C showing that electric charge was quantized.

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The Existence of Quarks (#4)

23. Less than a century after Mendeleev released his "periodic system" in 1869, scientists thought that all ______ was composed of three fundamental particles: protons, neutrons, and electrons.

24. In 1912 cosmic rays were discovered. By the late 1930's the behavior of new cosmic ray particles could not be explained with the currently accepted three fundamental particles. In the 40's and 50's many "cosmic ray" particles; such as lambdas, pions, sigmas and deltas, were being created in man-made particle accelerators (such as Earnest Lawrence's linear accelerators and cyclotrons and the Wilson Cloud Chamber). By the mid 1960's over 80 "fundamental particles" had been discovered and particle physicists nicknamed them the particle ______.

25. American physicist ______ ______ restored order and elegance back to nature. He noticed patterns in both the newly discovered particles along with the already known protons, neutrons, and electrons that could be explained by underlying symmetries and broken symmetries. He earned the Nobel Prize for Physics in 1969 for his research. He named his new set of basic building blocks quarks.

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The Standard Model of Particle Physics (#5)

26. In 1968, at the Stanford Linear Accelerator, they used a high energy electron beam to take an electron micrograph of the proton. They found experimental evidence that the proton was made of three objects with the correct charges. This confirmed the ______ theory.

27. The 12 particles that had no discernible internal structure were then arranged in a table similar to Mendeleev's periodic table of elements. This table contained three families (or generations) with "everything in the world around us" being composed of the four members in the first family. The remaining eight particles formed the second and third generation families were exactly the same as those in the first family except that they were ______. NOTE: This video was made prior to the discovery of the Higg's Boson in 2012.

28. The letters LHC stand for the ______ ______ ______ which is currently the world's highest energy particle accelerator operated by CERN and located in Switzerland.

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Electron Orbitals

Bohr's model of the atom with electrons moving in precisely predetermined circular orbits only truly explained the behavior of the single electron of Hydrogen. When his mathematics were applied to higher order atoms (even Helium Z = 2) they failed.

29. Today we say that an atom's electrons are present in probability clouds since ______ theory restricts (1) our ability to know exactly where an electron is located at any given moment of time, and (2) how much energy an electron has at any specific moment of time. The image shown above reveals today's concept of how a neon atom's 10 electrons might "look" or be distributed.

30. ______ ______ ______ requires that no two electron be in the same quantum state. Without this requirement all electrons in any element could be in the same ground state with no volume or unique chemical property.

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Gravity and Electromagnetism (#7)

31. ______ is the weakest force in the universe,

32. ______ is the force that (1) held the bubbles together, (2) allowed the flame to burn, (3) allows us to push and pull things, (4) see everything in the world around us, and (5) the force that allows your TV set to work. It holds the electrons in place around the nucleus and the molecules together to form structures.

33. The apple does not sink into the palm of Dr. Cox because of the ______ between the electrons in the apple and the electrons in his palm.

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Unification of Electricity and Magnetism (#8)

34. 2000 years after the Greeks noticed that a piece of amber stroked against fur could attract feathers and that certain rocks were attracted to iron, it was ______ ______, a 19th century experimental physicist, who discovered that electricity and magnetism were different manifestations of the same force.

Dr. Cox examined one of this scientist's original notebooks at the Institution of Engineering and Technology in which there was a reference to his most famous discovery: "Convert Magnetism into Electricity."

35. This phenomena was accomplished by ______ a magnet inside a coil of wire to generate electricity.

In 1865, these two phenomena were unified mathematically into a single framework by ______ ______ ______. Einstein called his revolutionary equations "the most profound and fruitful that physics has experienced since the time of Newton."

36. Critical to our course is an important mathematical consequence of these equations, the theoretical speed of electromagnetic waves.

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The Strong and Weak Nuclear Forces (#9)

37. The ______ nuclear force is responsible for holding the nuclei of atoms together and keeping the atom from spontaneously exploding as a result of electromagnetic repulsion.

38. Positron Emission Therapy (PET) uses a radioactive tracer to look for disease. PET scanner technology is a direct spinoff of particle physics research. During radioactive beta decay, both positrons (anti-matter electrons) and electrons are emitted. In 1934 Enrico Fermi solved the problem by proposing the ______ nuclear force which allowed neutrons to transmute into protons and vice-versa while at the same time emit electrons or positrons and neutrinos.

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Unified Theory of Forces (#10)

39. In the 1960's scientists were able to mathematically unite the electromagnetic force and the weak nuclear force into the single ______ force.

Image courtesy of R. Nave at http://hyperphysics.phy-astr.gsu.edu/hbase/astro/unify.html#c1

40. The ______ ______ ______ might eventually be able to unite all four fundamental forces into the single force that is believed to have existed briefly 10^-43 seconds after the Big Bang.