Stefan Bischof
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 Apr 19 comment Focal Length Calculation Your posted company Thorlabs has good online ressoures concerning working distance WC and focal length f. Post a separate question after studying these resources. Apr 19 comment Rain drop sliding on car windshield @Stealthmate Surface tension of water-glass surface determines contact angle to your windshield. Cleaning solvents will change this contact angle and area of contact. Apr 16 comment Focal Length Calculation You may select distance in parallel beam path arbitarly in geometric optics. Think about the lines in your diagram of a perfect parallel beam path: nothing will change the parallel lines until they refracted by a lens. Apr 16 comment Focal Length Calculation Improve your question by asking about a physics concept. You already learned focal length is related to making a perfect point source to a perfect parallel beam. Read about this geometric optics. Please feal free to ask specific questions about imperfect point sources - real sources. Apr 16 comment Focal Length Calculation +1 Yes, $f_2=d_5$. However I see from the sketch $d_1\neq d_{source}$ If it is also equal, than you are right. Apr 16 comment Focal Length Calculation +0 Welcome to physics SE! This question has no answer, if you do not define two things. a) $d_{source}\neq d_1$ and b) diverging angle $\theta_{source}$ which your laser may provide in its manual as an FWHM angle. Adding this information will earn you +1 Mar 22 comment Rain drop sliding on car windshield Surface pressure of the water-glas interface simplified to friction is neglected? Mar 17 comment Clarification from Griffiths Introduction to quantum mechanics +1 Welcome to Physics SE.. Mar 15 comment Newton's rings experiment +1 Excellent to mention less contrast as well. Mar 15 comment Newton's rings experiment +1 Oh right, I didn't know that. Logical because omitting reflection in center. Mar 15 comment Free falling and bouncing back +1 Welcome to physics SE! :) I understand your question, but try to phrase the question more focused on the concept of acceleration on when hitting ground. Mar 15 comment Newton's rings experiment -1 Welcome to Physics SE! Sorry, that your first answer is wrong. We are not talking about bright field illumination. The dark ring occurs because of an optical phenomenon called "destructive interference". Keep following the SE. :) It is a great place to learn. Mar 13 comment What does the $k_e$ in Coulomb's law and $G$ in Newton's Universal Gravitation Law mean? +1 A warm welcome to physics SE! :o) Learn how to use MathJax by looking at the changes at your post by clicking at the edit button at the left bottom corner. Mar 12 comment Is it possible to 'push' a path to the Earth's core? A warm welcome to Physics SE! :) I'm looking forward to see an answer including friction forces or fluid dynamics under high pressure to solve this ;) Mar 12 comment Help with a bungee jumping question Welcome to Physics SE! We encourage to ask about concepts you don't understand. Homework policy focuses to pose questions, helping to understand a broader scope than just the one question. Once a concept is understood, you are given the oportunity to answer similar questions by yourself. Mar 12 comment Is gravitational wave a new category of wave? Welcome to Physics SE! :) Mar 12 comment Amplitude-Modulated Wave in a Dispersive Medium Welcome to Physics SE! We encourage to ask about concepts you don't understand. Homework policy focuses to pose questions, helping to understand a broader scope than just the one question. Once a concept is understood, you are given the oportunity to answer similar questions by yourself. Mar 9 comment Why is this laser beam being scattered(and not)? However intensity of one reflection follows the rule of thumb at perpendicular incidence of R=4%. Your explanation requires at least two reflections: 0,16% intensity. Times two from front and back of tube wall. Adding intensity of higher orders does not help further. Mar 9 comment Why is this laser beam being scattered(and not)? The air filled system can be modelled with a lens system of two thin lenses. Mar 8 comment Why is this laser beam being scattered(and not)? See Cylindrical lens in wikipedia.