A team of marine biologists is using sonar (sound waves) to map the seabed. They are using a sonar frequency that produces a wavelength of 5.0 cm in water. They notice that when the sonar waves encounter a particular trench on the seabed with an opening of approximately 10 cm wide, the waves spread out significantly after passing through the opening.
Explain why this spreading (diffraction) occurs and how it affects the resolution of the sonar image they obtain of the trench. Relate your explanation to the ratio of wavelength to the gap width and the limitations this imposes on the sonar’s imaging capabilities.
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Create Free Account Log inThis is a free VCE Units 3 & 4 Physics practice question worth 4 marks, testing your understanding of Diffraction & imaging. It falls under How has understanding about the physical world changed? in Unit 4: How have creative ideas and investigation revolutionised thinking in physics?. Submit your answer above to receive instant AI-powered marking and personalised feedback.
A complex interplay exists between theory and experiment in generating models to explain natural phenomena. Ideas that attempt to explain how the Universe works have changed over time, with some experiments and ways of thinking having had significant impact on the understanding of the nature of light, matter and energy. Wave theory, classically used to explain light, has proved limited as quantum physics is utilised to explain particle-like properties of light revealed by experiments. Light and matter, which initially seem to be quite different, on very small scales have been observed as having similar properties. At speeds approaching the speed of light, matter is observed differently from different frames of reference. Matter and energy, once quite distinct, become almost synonymous. In this unit, students explore some monumental changes in thinking in Physics that have changed the course of how physicists understand and investigate the Universe. They examine the limitations of the wave model in describing light behaviour and use a particle model to better explain some observations of light. Matter, that was once explained using a particle model, is re-imagined using a wave model. Students are challenged to think beyond how they experience the physical world of their everyday lives to thinking from a new perspective, as they imagine the relativistic world of length contraction and time dilation when motion approaches the speed of light. They are invited to wonder about how Einstein’s revolutionary thinking allowed the development of modern-day devices such as the GPS. A student-designed practical investigation involving the generation of primary data and including one continuous, independent variable related to fields, motion or light is undertaken either in Unit 3 or Unit 4, or across both Units 3 and 4, and is assessed in Unit 4, Outcome 2. The design, analysis and findings of the investigation are presented in a scientific poster format.
In this area of study, students learn how understanding of light, matter and motion have changed over time. They explore how major experiments led to the development of theories to describe these fundamental aspects of the physical world. Students consider the limitations of classical mechanics as they explore Einstein’s view of the Universe. They use special relativity to explore length contraction and time dilation as observations are made by observers in different frames of reference, and the interrelationship between matter and energy.
Investigate and explain theoretically and practically diffraction as the directional spread of various frequencies with reference to different gap width or obstacle size, including the qualitative effect of changing the ratio λ / gap, and apply this to limitations of imaging using electromagnetic waves.
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