Physics: Quanta to Quarks Option (99.95 ATAR)

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1 HSC Physics Year 2016 Mark Pages 22 Published Jan 15, 2017 Physics: Quanta to Quarks Option (99.95 ATAR) By Edward (99.95 ATAR)

Powered by TCPDF (www.tcpdf.org) Your notes author, Edward. Edward achieved an ATAR of 99.

2 Powered by TCPDF ( Your notes author, Edward. Edward achieved an ATAR of in 2016 while attending Barker College Currently studying at The University of Sydney Achievements: ATAR: English Advanced: 96 Chemistry: 95 Physics: 95 Maths Extension 1: 99 Maths Extension 2: 94 Music 2: 97 Music Extension: 49/50 Edward says: In 2016, I achieved an ATAR of I was Dux of Barker College in 2016, and achieved Band 6's in all 13 units that I completed (see above for my HSC marks). My clear, detailed notes are what allowed me to achieve these results. My notes are very thorough and they are written in a way that is easy to understand. They contain all the key points needed to achieve full marks in responses.

3 Edward Koorey Physics Module 4 Quanta to Quarks Model of the Atom: Thomson s Plum Pudding Model: Atoms are solid lumps of positive charge with small symmetrical cathode rays/electrons scattered evenly amongst this Has a very low electric field strength as the charges are so close together Rutherford Model of the Atom: Two things surprised Rutherford when he did an experiment of scattering alpha particles with gold foil. He expected the alpha particles to pass through with slight deflection. Firstly, some of the alpha particles reflected back/experienced deflections greater than 90 (didn t actually touch the positive nucleus). This suggests that the positive alpha nucleus was rebounding off a positive, high density area in the gold foil (the positive nucleus). The amount of alpha particles scattered through angles of more than 90 was 1 in Secondly, many passed through without deflection. This suggests that matter is mostly made up of empty space. Indeed, 99.9% of the mass of the atom was contained in the tiny nucleus. Rutherford s model paralleled the planetary orbits. There was the dense positive nucleus that had most of the matter, and then a lot of empty space around the nucleus that had electrons orbiting around the protons, in orbits that he believed should be unstable. The radius of an atom was m but the radius of the nucleus was about m, so most of the mass was concentrated in the centre in a small amount of space. Limitations of the Rutherford planetary model: Didn t explain: What the nucleus was made of (just that its positive and dense) How are the orbits structured/arranged Why the negatively charged electrons wouldn t spiral downwards towards the positive nucleus Rutherford s atomic model was not stable the electrons are accelerating since they have centripetal motion, and this would mean that they would radiate

4 Edward Koorey energy and spiral into the nucleus, releasing the full spectrum. But this doesn t happen. Planck s contribution to quantized energy: Planck proposed a theory to model the spectrum of a black body. This theory dictated that the energy of oscillations of atoms or molecules cannot have just any value; they can only possess a discrete amount of energy that is a multiple of the minimum value related to the frequency of oscillation by the equation E=nhf. So energy is not a continuous quantity but rather is quantized into discrete packets. Max Planck solved the UV catastrophe by creating a new black body radiation curve based on experimental results and his own theory. He suggested that the emitters in the walls of the cavity can only have energies E given by E = nhf. The emitters can absorb or radiate energy in packets or quanta. Two consecutive energy states of an emitter differ by hf. Planck made huge contributions to the quantum theory of physics. He suggested that Radiation (energy) is not emitted/absorbed by black bodies as continuous waves like in Classical physics, but rather is emitted/absorbed in little bursts or packets of energy quanta. Spectral Analysis: There are two types of spectra: absorption spectra and emission spectra. Absorption spectra can be produced by passing white light (a continuous spectrum) through a cool gas. The atoms or molecules in the gas will absorb certain specific wavelength (colours) of light. The atom that absorbed the light is now in an excited state and will spontaneously emit a photon of light, usually in a different direction. Therefore the original beam of light will now have certain wavelengths depleted (that have been absorbed) and these will appear as a series of dark lines when observed through a spectroscope. Emission spectra can be produced when a gas is excited. This can be achieved by heating the gas or passing an electrical current through a low pressure gas. The light produced when viewed with a spectroscope will often be made up of a series of bright coloured lines.

Edward Koorey Bohr s model of the atom: Significance of the hydrogen spectrum to Bohr: It was experimentally known that chemical elements produce line spectrum when they emit light.

5 Edward Koorey Bohr s model of the atom: Significance of the hydrogen spectrum to Bohr: It was experimentally known that chemical elements produce line spectrum when they emit light. A line spectrum is a set of certain particularly wavelengths. The wavelengths in the visible region for the hydrogen spectrum were measured. A formula was fitted to these wavelengths but it could not be explained until Bohr developed a model of the hydrogen atom, using Planck s idea of quantized energy to develop 3 postulates. Bohr derived the Rydberg equation for the hydrogen spectrum using his postulates. Bohr s model assigned positions to the electrons and said that their energy levels were quantized. He had the radical idea that electrons had energy states and could absorb and emit energy to change states but he had no evidence. The Rydberg/Balmer equation gave him evidence for the quantized emission from the hydrogen atom, allowing him to further his model and define his postulates. Bohr s postulates: Bohr revised Rutherford s planetary model of the hydrogen atom. He based his changes upon the quantisation of energy and the angular momentum of the electron. He had three postulates that addressed the limitations of the original Rutherford model:

6 Powered by TCPDF ( Edward Koorey 1. Electrons exist in stable orbits. An electron can exist in any of several special circular orbits with no emission of radiation. These orbits are called stationary states. Each stationary state is designated by an integer called a quantum number. N=1 indicates the ground state. 2. Electrons absorb or emit specific quanta of energy when they transition between stationary states (orbits). When an electron jumps down from a higher stationary state to a lower one, it emits a quantum of radiation - E = hf. 3. Angular momentum of electrons is quantized. An electron in a stationary state (orbit) has a quantized angular momentum that can only take values of mvr = nh 2π. Structure of the Bohr (Rutherford-Bohr) model: Small positively charged nucleus that contained most of the mass Electrons orbit in circular paths Electrons do not radiate energy continuously due to the quantisation conditions of energy associated with each electron orbit When an electron jumps to a higher or lower orbit, it will absorb or emit a quantum of energy in the form of a photon. Balmer series: Balmer did a detailed study of the visible emission spectrum for hydrogen, which is now referred to as the Balmer series. Rydberg generalized Balmer s equation to: λ = wavelength of the spectral line R = Rydberg s constant (1.097 x 10 7 m -2 ) nf = the final orbital shell of the electron ni = the initial orbital shell of the electron The Balmer series is for electrons that are excited and then fall back to n=2. Lowest energy jump is red (ie 3-2)

Physics 1C Lecture 29A. Finish off Ch. 28 Start Ch. 29

Physics 1C Lecture 29A. Finish off Ch. 28 Start Ch. 29 Physics 1C Lecture 29A Finish off Ch. 28 Start Ch. 29 Particle in a Box Let s consider a particle confined to a one-dimensional region in space. Following the quantum mechanics approach, we need to find