What is Modern physics: Definition and 253 Discussions

Modern physics is a branch of physics either developed in the early 20th century and onward or branches greatly influenced by early 20th century physics. Notable branches of modern physics include quantum physics, special relativity, and general relativity.
Classical physics is typically concerned with everyday conditions: speeds are much lower than the speed of light, sizes are much greater than that of atoms, and energies are relatively small. Modern physics, however, is concerned with more extreme conditions, such as high velocities that are comparable to the speed of light (special relativity), small distances comparable to the atomic radius (quantum mechanics), and very high energies (relativity). In general, quantum and relativistic effects are believed to exist across all scales, although these effects may be very small in everyday life. While quantum mechanics is compatible with special relativity (see relativistic quantum mechanics), one of the unsolved problems in physics is the unification of quantum mechanics and general relativity, which the Standard model (of particle physics) currently cannot account for.

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  1. adamaero

    Crystallography, diffraction, identifying the pure element

    Homework Statement The only things you know about the sample are: (i) it has some kind of cubic lattice, and (ii) it is a pure element. Identify the element in the crystalline sample. SC: R = 0.5a FCC: R = 0.25a√2 BCC: R = 0.25a√3 Distances from Bragg peaks: d1 = 0.2037 nm d2 = 0.1746 nm d3...
  2. adamaero

    Given wavenumber find spring constant harmonic oscillator

    Homework Statement The separation between energies of an oxygen molecule is 2061 cm-1 (wavenumber). Treating the molecule as a simple harmonic oscillator whose fundamental frequency is related to its spring constant and reduced mass, calculate the spring constant for an O2 molecule. meff =...
  3. adamaero

    Finding wavelength of visible light in a well

    Homework Statement Determine what colors of visible light would be absorbed by electrons in an infinite well, N = 3.1 nm. The effective mass for an electron is one-fifteenth of the standard electron mass. Homework Equations En = n2h2/(8mL2) E = hf f = c/λ The Attempt at a Solution E1 =...
  4. G

    What Colors of Light Are Absorbed by Electrons in a 3.1 nm Infinite Well?

    Homework Statement Determine what colors of visible light would be absorbed by electrons in an infinite well, N = 3.1 nm. The effective mass for an electron in GaAs is one-fifteenth of the standard electron mass. Homework Equations En = πh2/[2*N2*me/15]*n2 L = nλ/2 Ψ = √(2/L)sin(nπx/L) The...
  5. adamaero

    Ground state energy for exciton in Si

    Homework Statement Estimate the ground state energy (eV) for an exciton in Si. εSi = 12 ε = 1.0359×10−10 Effective masses me* = 0.26me mh* = 0.36me effective mass = 0.15me Values of h 6.626×10−34 J⋅s 4.136×10−15 eV⋅s Values of ħ Units 1.055×10−34 J⋅s 6.582×10−16 eV⋅s Homework Equations E1 =...
  6. adamaero

    Bohr Model applied to Excitons

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  7. maxhersch

    Testing Difficulty with Modern Physics Midterm

    I am currently in Honors Physics 3 which is the third introductory course of my physics degree program and covers modern physics beginning with special relativity. So far we have covered Lorentz transformations and velocity additions, relativistic energy and momentum, blackbody radiation, photon...
  8. D

    Modern Physics question -- an atom ejecting a relativistic electron

    Homework Statement . An atom at rest can undergo radioactive decay, ejecting an electron at a maximum speed of 0.5c. If the atom in a particle accelerator is observed to produce an electron traveling at 0.75c, at least how fast must the atom itself have been moving? Homework Equations u0 x...
  9. Katyan Anshuman

    I What is Quantum Decoherence and How Does it Affect Quantum Systems?

    So I whilst understanding basics of some quantum phenomena like superposition, tunnelling, fluctuations etc I happened to watch the movie "Coherence" where there's a scientifically unsatisfactory reference to quantum decoherence. What exactly is this concept?
  10. Titan97

    Studying Undergraduate Physics: Study Modern Physics & Get Concepts Clear

    My college started physics course with light and blackbody radiation. I am facing difficulties in understanding relativistic energies, Compton effect and specific heats of multi atomic gases. Can you suggest a method for studying modern physics and suggest some good books for getting my concepts...
  11. Y

    What is Theoretical Physics and How Can It Be Discussed Without Math?

    Physics is one of my most favorite topics, particularly Theoretical Physics. I have no formal education in Physics but I read quite a bit Physics material and also some Physics books. I have B.Sc. in Materials Science and Engineering. I like to discuss advanced physics ideas logically and...
  12. T

    Other Junior-level Modern Physics textbook suggestions

    Hello All, I am looking for suggestions for a junior-level Modern Physics textbook to read over the summer for the purpose of preparing me to take senior-level Quantum Mechanics in the fall. I have a solid Math background so a text that would possesses some level of mathematical rigorousness...
  13. CrunchBerries

    Classical University Physics with Modern Physics by Bauer/Westfall?

    Good day, I made a purchase of this book by Bauer-Westfall, then realized I was looking for the Young/Freedman version. Did I get a good book or is this a paper weight? I am using this for self study from Newton to E&M along with Single Variable calculus. Any general opinions? Get another...
  14. John Jacke

    General Physics 2 vs Modern Physics

    I'm finishing up my general physics 2 course (today actually) and I begin my upper division courses in Fall. I was wondering how you found general physics 2 compared to intermediate modern physics in terms of difficulty? I found physics 2 (basically introductory E&M at my school) more difficult...
  15. L

    Algebra Books that mix modern physics with algebra and geometry

    Hi I'm an advanced undergraduate physics student and I'm currently searching books for my career project. The topic I selected is titled: Algebra and geometry in modern physics. So I'm currently looking for books that cover modern aspects of physics in a more mathematical approx. In specific I'm...
  16. Aafia

    I How can we distinguish classical physics and modern physics?

    How to decide whether a particular topic is studied in classical physics or modern physics?
  17. A

    I Quantum field and mediating particles

    I'm not sure if I posted this in the right category, it's something that came up just after the quantum mechanics section so I just chose this one. I've come across something that I simply can not find an answer for on my own. I'm taking Modern Physics course and the last chapter is some...
  18. A

    What is the Photon Flux for a 100 MHz Signal Traveling 4 Light Years Away?

    Homework Statement It's in attachment Homework Equations E=hf. Where h= planks constant and f= frequency The Attempt at a Solution I know that the flux of a photon is (# of photons)/(sec m^2) I don't know the number of photos but I do know the frequency and power. E=(6.6261*10^(-34)) J•s *...
  19. W

    Modern Physics, Mech, or ElectroMag?

    I have three courses to choose from, pick two. They are Introduction to Modern Physics, Mechanics 1, and Electromagnetism 1. Which should I choose? I have picked Modern Physics and Mechanics 1, but I almost want to do Mechanics 1 and Electromagnetism 1, but since it's my first semester at the...
  20. W

    Modern Physics Question: Davisson and Germer Expt. beam diffraction

    Homework Statement In the experiment of Davisson and Germer (a) show that the second- and third-orderdiffracted beams cannot occur and (b) find the angle at which the first-order diffracted beamwould occur if the accelerating potential were changed from 54 to 60 V. (c) What...
  21. X

    Expressing A Quantity In Polar Coordinates?

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  22. fresh_42

    Exploring the Extended Riemann Hypothesis in Modern Physics

    I just thought about the critical concepts in mathematics and physics that arose in the last century: Goedel, Schroedinger, etc. My question is: Are there any physical theories that rely on the validity of the extended Riemann Hypothesis? I don't mean computer science, i.e. secure...
  23. E

    Welcome to PF: A Beginner's Guide to Scientific Forums

    Hello, I'm Newbie here. Please be kind to me.
  24. S

    Kaon Decay -- Special relativity

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  25. O

    Intro Physics Suggestions for conceptual E&M and modern physics reading

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  26. E

    Deriving the Compton Effect Equation: A System of Equations Approach

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  27. ira

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  28. Roger Dodger

    Book Suggestions for Teaching Conceptual Modern Physics

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  29. T

    Newtonian space in modern physics

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  30. T

    B Exploring Newton & Aristotle's Views on Space in Modern Physics

    I've been wondering if space as understood by Newton, as an actual thing that contains matter, is relevant to modern physics. Has Newton's idea been disregarded? Is Aristotle's view that there is no space-vacuum now accepted? Thanks
  31. Christian Grey

    Quantum Where Can I Find a Comprehensive Introduction to Modern Physics Theories?

    Can someone recommend me a modern physics book, that includes introduction to all the different theories like quantum mechanics,quantum field theory,special relativity,general relativity,standard model,string,m-theory,supersymmetry,superstrings,quantum gravity,loop quantum gravity etc(if I...
  32. A

    Is irodov chapter on light the level of Ipho?

    Hi,I am new to this website and this is my first question. I just wanted to ask if irodov's chapter on light is of Ipho level or is it beyond that(that is it for 2nd or 3rd year undergrads) and Aldo what about modern physics. I would have no problem with that but if that is true then I will...
  33. C

    Atomic Best book on Modern Physics? 5 choices, suggestions?

    Hi everyone, I'm looking for an introductury book (or several books) on modern physics that explains the history and experiments the led to the understanding of the atom, the electron, avogadros number, Plancks constant, rutherford, quantum mechanics etc. I want an idea of how all the...
  34. ognik

    Other Good pre-honours 'revise all physics' type book(s)

    Hi - I'm doing an honors degree in physics by distance learning, having received my B.Sc around 20 years ago. I find there is a lot that is presented quite differently, and also stuff that I don't remember well enough - or not at all. So I'm looking for the fewest books that I can use to...
  35. U

    Math requirement for Modern physics by Kenneth Krane?

    What math should a person know to THOROUGHLY understand everything in this textbook? (For refrence) cal2 (integration) cal3(mulit-variable) diffeq1(ode) diffeq2(pde) linealg vectorcalc realanal1 realana2 amazon link -http://www.amazon.com/Modern-Physics-Kenneth-S-Krane/dp/0471828726
  36. A

    Readings for a general understanding of Quantum Field Theor?

    Hi all, I have an undergraduate degree in Physics, but I've since specialized in more environmental applications of Physics. I've taken a few quantum Physics courses as part of my degree, but, if I'm being honest, what I took from those courses was more of a mathematical view of the field, such...
  37. U

    Hi all, I'm a Usman,a physics student from Pakistan

    Hi all, I'm a Usman,a physics student from Pakistan .I have joined this forum to polish my physics skills and to share whatever I know about physics ,its principles and so many on......:smile::smile::smile::smile::smile::smile:
  38. A

    Sketch the wave, showing both x < 0 and x > 0.

    Homework Statement [/B]A wave is represented by the wave function: y = A cos(2πx/λ + π/3) for x < 0. For x > 0, the wavelength is λ/2. By applying continuity conditions at x = 0, find the amplitude (in terms of A) and phase of the wave in the region x > 0. Sketch the wave, showing both x < 0...
  39. M

    I am trying to find materials to make a pulse laser for lab

    Hello everyone, I am working with my modern physics professor Dr. Parshar to make a pulse laser for my modern physics lab. I have to make an itemized expense report for the materials and all that. I need help figuring out what crystal or doped glass would be best to use, not super expensive...
  40. J

    Intro Physics Modern physics coverage Halliday/Resnick/Krane 4E extended

    How much additional material is in the extended version of Volume 2--how many additional chapters on what topics? Is it worth getting an extended edition copy for the additional modern physics material if one already has the non-extended version (and Young and Freedman 11E)?
  41. U

    Intro Physics University physics with modern physics

    Ok, currently I am studying a book called University physics with modern physics. I am only studying classical mechanics at the time. My question is, the modern portion part of it, is it about the same material taught in introductory modern physics class(state university) or do i have to get a...
  42. jaskamiin

    Is physics utilized in AI research? If so, how?

    It seems to me on the forefront that Artificial Intelligence research is more of the computer scientist's and mathematician's game, but I seem to recall reading a couple of books written by physicists on the subject as well (including Penrose's The Emperor's New Mind). Is this a popular trend...
  43. J

    What are the best modern physics books for a young astrophysics enthusiast?

    Hello guys. I am fortunate that I have found this website and I have created an account just to ask one question. I asked this on yahoo answers as well but no luck. So here goes. I'm 14 years old and I love astrophysics. I have learn most of the basic stuff and I've also read A brief history...
  44. AdityaDev

    Radiation pressure from light source

    The energy of photon is $$E=\frac{hc}{\lambda}$$ Now if we have an isotropic point light source of power P, Number of photons $$N=\frac{P}{E} = \frac{P \lambda}{hc}$$ Hence one can find the change in momentum and hence the force exerted by a beam or light sources. But let's say we keep an...
  45. A

    Modern Physics Text for self-study

    As the title implies, I am looking for a decent introductory modern physics text for self-study purposes. I'm a Biochemistry major, so this is partially for my own enjoyment and partially for preparation for Physical Chemistry II. I know that there are a lot of threads on this, but I always like...
  46. D

    How to know more about the frontiers of modern physics research?

    I'm a first year physics undergraduate. I'm trying to look for some research opportunities as becoming a physicist is always my target. However, I simply have no idea how the current research is going on, and before I approach any professors I guess I should already have some basic understanding...
  47. blintaro

    Prepping for first "Modern Physics" Class

    Hello people of the Physics Forums, this is going to be a bit of a long post, I apologize for that! I'm posting here to ask for some advice on how to prepare for my first sophomore-level modern physics class. I am feeling very nervous about this class because it is imperative I get top grades...
  48. M

    Perception of faster than light travel?

    I'm currently taking a modern physics course, I came across this problem which really threw me off guard: Three spaceships A, B, and C are in motion as shown in the figure. The commander on ship B observes ship C approaching with a relative velocity of 0.83c. The commander also observes ship A...
  49. G

    Modern Physics - Work Energy Theorem

    Homework Statement The work-energy theorem relates the change in kinetic energy of a particle to the work done on it by an external force: \triangle K = W = \int F\, dx . Writing Newton's second law as F = \frac{dp}{dt} , show that W = \int v\, dp and integrate by parts using the...
  50. J

    Is the simple explanation of modern physics ever the case?

    In QM for example, I realize it is pointless to try and picture what is happening because the is nothing macroscopic to base it on. In GR, we are told that something called space-time is curved which creates the phenomenon of gravitational force. The deeper you go into these subjects, however...
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