Light and Atoms Test 2021.pdf

Assessment Type 2: Skills and Applications Tasks Light and Atoms 2021 2021 PHYSICS Wednesday September 15, 2021. Time: 105 minutes Student Name...

Assessment Type 2: Skills and Applications Tasks Light and Atoms 2021 2021 PHYSICS Wednesday September 15, 2021. Time: 105 minutes Student Name: _________________________________________ Teacher: ______________________________________________ LIGHT AND ATOMS Approved calculators may be used Instructions to Students 1. The assessment is out of 94 marks. Use this as a guide to answering questions by allocating approximately 1 minute per mark. 2. All answers are to be written in the spaces provided. You may make notes on the scribbling paper, but this will not be assessed. 3. The equation sheet provided may be used, but no other notes are permitted. 4. Marks may be deducted if you do not clearly show all steps in the solution of problems, if you give answers with an inappropriate number of significant figures or with incorrect units, or if you do not define additional symbols. You should use diagrams where appropriate in your answers. 5. Use only black or blue pens for all work other than graphs and diagrams, for which you may use a sharp dark pencil. Page 1 of 16  Represent all numerical answers in scientific notation form with the appropriate units and number of significant figures. (KA4 – 5 marks) 1. A diffraction grating can be used to analyse light emitted from a range of sources. Light passes through hundreds of thin, closely-spaced slits, providing hundreds of individual sources of light that interact to produce an interference pattern. The pattern can then illuminate a screen or be observed through the telescope of a spectrometer: Slide containing three diffraction Experimental setup to observe a laser light gratings of varying precision interference pattern on a screen Bench top spectrometer (a) Explain how light passing through a diffraction grating can produce an interference pattern. ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ _________________________________________________________ (KA1 – 3 Marks) Consider the diagram below, depicting the position of a diffraction grating and screen, as well as the path of light from individual sources (depicted in red) coinciding at the mth maximum on the screen. mth maximum diffraction grating screen Page 2 of 16 (b) Using the diagram and the space below, derive the following expression describing the interference pattern observed. 𝑑 sin 𝜃 = 𝑚𝜆 where d is the distance between the slits and 𝜃 is the angular position to the mth maximum (m specifies the order of the maximum) ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ _________________________________________________________ (KA2 – 4 Marks) (c) The images below depict what is observed through a spectrometer when light from three different sources passes through a diffraction grating: Laser source Incandescent light bulb Gas emission tube image 1 image 2 image 3 Match each source to each image, and provide 1 reason to justify each match. Image 1: ____________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ Image 2: ____________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ Image 3: ____________________________________________________________ ____________________________________________________________________ _________________________________________________________ (KA1 – 6 Marks) Page 3 of 16 2. An experiment was performed in which light of different frequencies was incident on a metal surface. Electrons were emitted from the metal surfaces producing a photoelectric current. A backing voltage was then applied to negate the current and adjusted until the current was reduced to zero (at which point, the stopping voltage had been achieved). The following data was recorded: Frequency Stopping Voltage 5.0 × 10!" Hz 0.21 V 5.5 × 10!" Hz 0.40 V 6.0 × 10!" Hz 0.63 V 6.5 × 10!" Hz 0.78 V 7.0 × 10!" Hz 1.10 V (a) Using the grid on the next page, construct a graph* to compare the frequency (x-axis) to the stopping voltage (y-axis). Draw a line of best fit. (IAE2 – 5 marks) *ensure there is space to show the x and y intercepts of the line of best fit. (b) Using the graph, determine: i) The threshold frequency of the metal. ________________________________________________________________ ________________________________________________________________ ______________________________________________________ (KA2 – 2 Marks) ii) The work function of the metal. ________________________________________________________________ ________________________________________________________________ ______________________________________________________ (IAE3 – 3 Marks) (c) Using your graph, draw and label lines to depict the relationship between frequency and stopping voltage if: i) more intense sources of light were used. ii) a metal with a lower work function was used. (IAE3 – 2 Marks) Page 4 of 16 Page 5 of 16 3. The image below depicts the spectrum of x-rays produced from an x-ray tube. (a) Explain how a continuous range of frequencies is produced by an x-ray tube. ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ _________________________________________________________ (KA1 – 3 Marks) (b) Represent the following on the image above: i) Label the maximum frequency and characteristic x-rays on the spectrum shown (KA1 – 2 Marks) ii) Draw the expected spectrum if the voltage across the tube were reduced. (IAE3 – 3 Marks) Page 6 of 16  (c) Determine the maximum frequency of x-rays produced by a tube with 25 kV potential difference. ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ _________________________________________________________ (KA2 – 2 Marks) 4. One of the features of Australian banknotes are elements that fluoresce when observed under ultraviolet light, such as the Eastern Spinebill depicted on the $5 note. Using the energy level diagram below, represent and explain the process of fluorescence. ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ __________________________________________________________ (KA1 – 5 Marks) Page 7 of 16 5. The elements in a transmitting antenna used to transmit a television signal is aligned vertically, as depicted in the diagram below. Also depicted is the magnetic field associated with the transmitted electromagnetic wave (which oscillates in the horizontal plane): Direction of propagation (a) Using the space above, draw a representation of the electric field associated with the transmitted electromagnetic wave. (KA1 – 2 Marks) (b) State the plane of polarisation of the electromagnetic waves transmitted. __________________________________________________________ (KA1 – 1 Mark) (c) The antenna produces electromagnetic waves with a frequency of 219.5 Mhz. Determine the wavelength of the electromagnetic waves produced. ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ _________________________________________________________ (KA2 – 3 Marks) Page 8 of 16 6. In the Davisson-Germer experiment electrons were projected at the surface layers of a metallic crystal lattice with energy of 54 eV. The spacing d between atoms in the surface of the metal was 0.23 nm. (a) Show that the speed of the electrons is approximately 4.36×106 ms–1. ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ _________________________________________________________ (KA2 – 3 Marks) (b) Calculate the wavelength of electrons travelling at this speed. ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ _________________________________________________________ (KA2 – 2 Marks) (c) The intensity of electrons that reach the detector at various angles θ is measured. Calculate the angle of the first-order maximum. ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ _________________________________________________________ (KA2 – 2 Marks) Page 9 of 16 7. Consider the energy level diagram for a hydrogen atom, depicted below: (a) Using the space above, draw arrows to represent at least 4 transitions associated with the Balmer series within the hydrogen emission spectrum. (KA1 – 2 Marks) (b) By referring specifically to the energy level diagram, explain why only unique wavelengths of light are seen in the emission spectrum of gases. ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ _________________________________________________________ (KA1 – 3 Marks) Page 10 of 16 (d) Consider the emission spectra of various elements, shown below. State which one (i, ii, iii, or iv) represents the emission spectrum of hydrogen. Justify your answer by referring specifically to the energy level diagram depicted on the previous page. ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ _________________________________________________________ (IAE3 – 5 Marks) (e) Determine the wavelength (in nanometres) of light that would be emitted by an electron transitioning from the n=6 energy level in hydrogen to the ground state. State which region of the electromagnetic spectrum this light would belong to. ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ _________________________________________________________ (KA2 – 4 Marks) Page 11 of 16 8. Gauge bosons are particle which mediate the fundamental forces of nature. Draw lines to match the gauge bosons listed on the left, with the force they mediate on the right. (KA1 – 3 Marks) gauge boson force photon strong nuclear force gluon weak nuclear force Z boson electromagnetic force 9. Free neutrons are unstable and can decay into a proton. This occurs through the transmutation of down quark into an up quark (mediated by a W boson) (a) Circle all of the following which a neutron can be categorised as: (KA1 – 3 Marks) fermion baryon meson lepton boson hadron (b) State the charge of the W boson. Justify your answer. ____________________________________________________________________ ____________________________________________________________________ _________________________________________________________ (KA1 – 2 Marks) Page 12 of 16 (c) Consider the reaction shown below depicting free neutron decay. It represents the formation of an up quark from a down quark, and release of an electron and electron anti-neutrino. Show that this reaction is possible by demonstrating that charge, lepton number and baryon number are conserved. d → u + e! + 𝜈'e ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ _________________________________________________________ (KA1 – 3 Marks) (d) If the emitted electron interacts with its antiparticle (the positron), an annihilation event will occur, producing two gamma-ray photons (depicted in the reaction shown below). e! + e# → 2γ i) Show that this reaction is possible by demonstrating that charge, lepton number and baryon number are conserved. (KA1 – 3 Marks) ii) Determine the total energy released from the annihilation event. (KA2 – 2 Marks) ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ ____________________________________________________________________ Page 13 of 16 8. Consider the following information, published in a Cosmos Magazine article in February 2019: Searching for missing particles The Standard Model of particle physics has been confirmed many times, but it is far from complete. Alan Duffy reports. We have long sought to understand our world. That quest now involves projects larger than any one country. It may soon be at an end. But it has been far from elementary. The Ancient Greeks believed the world comprised just five elements: earth, air, water, fire and aether. In 1869, Russian chemist Dimtri Mendeleev added a deeper level of understanding – and complexity – when he proposed his Periodic Table of Elements. There are now 118 elements in all, and together they explain the chemical reactions and properties the Greeks noted of the world around us. As the twentieth century began, we learned that all of these elements are just a combination of the three subatomic particles: electrons, protons and neutrons. Unlike before, this deeper but more fundamental revelation reduced the complexity of nature, while providing greater insights into its properties. As that century – and its technology – advanced, so too did the number of “fundamental” subatomic particles. From pions to muons and more, a zoo of hundreds of strange short-lived particles (as well as their antiparticles) were uncovered. In 1964, Nobel Prize-winning physicist Murray Gell-Mann set out to simplify things again by proposing that these particles were in fact all formed from quarks held together by gluons. Take two “up quarks” and one “down quark” and you get a proton; two down and one up forms a neutron. Order was restored. Over the past decades the remaining fundamental building blocks of our world were identified, like the final pieces of a jigsaw puzzle, to form the Standard Model of Particle Physics. Combinations of quarks (held together by gluons) form hadrons such as protons and neutrons, orbited by a family of electron-like leptons each with a corresponding neutrino of almost imperceptible mass. Interactions between these particles in the Standard Model are mediated by four “force-carrying” particles, most famously the photon of electromagnetism, as well as the W and Z bosons and the aforementioned gluon. In 2012 the long- predicted final particle, the Higgs Boson (aka “the god particle”) was uncovered at the Large Hadron Collider (LHC). The Standard Model was finished. It was a triumph. It was also incomplete. There was no mention of gravity, or solid prediction for the dark matter that holds the galaxies together; and all efforts to explain the dark energy that appears to drive the accelerating expansion of the universe was off by 120 orders of magnitude. As before, it is likely the answer will come only after things get worse, with a more fundamental description of nature that clarifies an ever-messier situation. Page 14 of 16 Identify one of the key concepts of science as a human endeavour, and discuss how this is illustrated in the example on the previous page. __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ ______________________________________________________ (KA3/4 – 6 marks) Page 15 of 16  Extra Space __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ __________________________________________________________________ Page 16 of 16