Modern physics Definition and 256 Threads

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. A

    Reflection and Transmission of String Waves

    To obtain the amplitude of the reflected and transmitted wave, I consider that the initial pulse is traveling to the right and I use the boundaries condition: 1. y_i(x = 0) + y_r(x = 0) = y_r(x = 0) 2. dy_i/dx |_(x = 0) + dy_r/dx |_(x = 0) = dy_r/dx |_(x = 0) The expression for the incident...
  2. Skyxplorer

    Length Contraction Problem for a Rod in a Spaceship

    Shoudnt answer be A since for observer in spaceship rod is at rest.
  3. J

    A problem in this photoelectric effect experiment

    (a) is easy. No i. Therefore, the 1kΩ resistor and the 3.20kΩ one are connected in series. So 'I' can be easily determined and so is VAC (b) is the same as (a) (c) The work function should be solved for via the equation eV₀=hυ-φ, where V₀ is the absolute value for VAC from part (b) (d) I am...
  4. N

    Intro Physics How useful is the "with Modern Physics" section of Tipler's Physics?

    I originally owned Tipler's Physics for Scientists and Engineers with Modern Physics; however, after several house moves, it needed a replacement. So, I bought it again, not realising that the version I bought doesn't have the "Modern Physics" chapters (34-41). How useful are these sections of...
  5. Slimy0233

    Relativity Studying Modern Physics, need book recommendations

    I am studying for an Masters Entrance exam called IIT JAM in India and this is my syllabus for Modern Physics. I would be grateful to you if you were to point out a book Easy to read and understand Good for a beginner in Modern Physics Good illustrations and examples (if possible) Which...
  6. P

    Is undergraduate modern physics hard?

    How hard is it compared to undergraduate thermodynamics? Is it harder or easier?
  7. P

    Undergraduate modern physics and condensed matter physics courses

    Do they really teach and help anything? I am taking them for my nanoengineering undergraduate program. The textbooks are solid state physics by j r hook and concepts of modern physics by mcgraw hill and r b singh introduction to modern physics and introduction to quantum mechanics by david j...
  8. gleem

    Approaches for teaching Modern Physics in Grade School and University

    [Mentor Note -- thread spun off from a thread in the Advisor forums] Both Feynman and Einstein have famous quotes about explaining physics concepts to those not well schooled in physics.(freshman undergrad and a six year old respectively). Yet both hedged a bit on this: Einstein Things should...
  9. Demystifier

    Intro Physics Weinberg, Foundations of Modern Physics (2021)

    Steven Weinberg wrote a book again. Did anyone read it? https://www.amazon.com/dp/1108841767/?tag=pfamazon01-20
  10. E

    I Does charging my phone increase its gravitational force?

    If the statement above is correct, I do not understand this concept. I guess by charging my phone I am not producing matter. Does it mean in this case, energy converts to mass (not matter)? Can someone please explain this?
  11. U

    Studying Modern physics after quantum mechanics

    Hello everyone. I am studying physics as a self-study and would like advice on the next topics to study. So far I have been studying: -calculus, linear algebra and basic physics -classical mechanics (from Goldstein's textbook) -classical electrodynamics and special relativity (from Griffiths...
  12. R

    Quantum Modern Physics Textbook Recommendations for Top-Tier Universities

    I seek current textbook recommendations for Modern Physics (Relativity, Quantum, Nuclear, Particles), upper undergraduate and graduate level, preferably that which are used at top-tier universities. Suggestions appreciated.
  13. H

    Quantum Elements of Modern Physics book recommendations?

    Hello, undergrad Physics student here. I have a course called "Elements of Modern Physics" this semester. Looking for some good book recommendations. Note that I need a book for self-study as I have decided to skip out on lectures because they are online right now and combined with a bad prof...
  14. Gabrielmonteiro

    I On the Rydberg Constant and the Emission Lines

    With regard to Rutherford's atomic model, and Rydberg's discovery in general for the hydrogen distribution lines, what does Rydberg's constant physically mean? Its unit is m ^ -1, as if it were a rate, but it was not clear to me its physical meaning. And why does it grow with atomic mass...
  15. R

    Intro special relativity problem regarding time dilation

    This example is worked out in the book, and at the beginning, they make the assumption that the muon is traveling at c, and then find the change in time from the Earth reference frame using delta t=100km/c. Then delta t is plugged into the time dilation equation on the left side and we solve for...
  16. Adams2020

    I The center of mass & relativistic collisions

    In special relativity (especially relativistic collisions), is the center of mass frame as useful as Newtonian mechanics?
  17. RUTA

    Insights A Principle Explanation of the “Mysteries” of Modern Physics

    Continue reading...
  18. RUTA

    Insights Modern Physics Understood as an Unrecognized Kuhnian Revolution

    Continue reading...
  19. hnnhcmmngs

    How Can Separating Variables Show Scale Factor Growth in Friedmann Equation?

    I was shown that adot^2/a^2 = c/a^3, adot = c / √(a), then da/dt = c / √(a) . Then I was told that I have to integrate this, but I don't understand where to go from there or how this will show me that the scale factor grows as t^(2/3).
  20. Zeynaz

    Calculating Electron Emission and Reflection in the Photoelectric Effect

    The full questions is in the picture. I already solved a) and found 5.6E14 electrons per second For b) i first found the power of the light but just multiplying the intensity with the area: (6.0 W/m2)(3.5E-4 m^2) = 0.0021 W Then I tried to use the voltage from the graph but i am not sure which...
  21. AlphaLibrae

    Find the wavelengths Kα, Kβ , Lα and Lβ from elemental Cu

    Homework Statement Problem: "What are the wavelengths of the characteristic Kα, Kβ , Lα and Lβ x-rays emitted from copper? Remember to use a Rydberg constant with the reduced mass correction made for elemental copper." Givens: Energy levels given: Kα (2,1) Kβ (3, 1) Lα (3, 2) Lβ (4, 2)...
  22. Bheshaj

    I What is the significance of the radioactive decay constant?

    What is the significance of the radioactive decay constant?
  23. Mason Smith

    Showing that the P(r) is maximum at r=a_0/Z

    Homework Statement Homework Equations where The Attempt at a Solution I tried to integrate (7-32) over all values of r (i.e., from negative infinity to positive infinity) and set it equal to 1, but the result was too messy and was divergent. Am I making the right approach?
  24. universal2013

    I Exploring Maxwell Equations & Hyperbolic Functions

    I am trying to understand why maxwell equations are correct in any reference frames? While i started to understand of his laws of physics a bit i could not imagine why he uses hyperbolic functions such as coshw instead of spherical ones in position and time relation between moving frames...
  25. Mason Smith

    Finding the 10 lowest energy levels

    Homework Statement Homework Equations The Attempt at a Solution I understand the equation, and I understand the concept. My question is this: What is the best way to go about solving this problem? My line of reasoning concludes that the fourth lowest energy level is E211. However, the...
  26. J

    How to teach modern physics for the visually impaired?

    What is the best way to approach the issue of temporal dilation in a class of the visually impaired?
  27. R

    Quantum Self education in modern physics

    In my physics education, I shied away from heavily theoretical stuff like General Relativity. I took the required sequence in Quantum Mechanics but having never used it on the job, much of that knowledge has faded too. I started a course in Quantum Field Theory but dropped it. I had friends...
  28. Quantumfied

    What if a modern physics textbook found itself back in time

    Okay guys, I’ve been wondering how different would the world be if something as simple as my calculus based physics textbook found itself back in time around 300 years ago. For the sake of the argument assume some rift opened up and swallowed my book sending it back to the year 1720. Let’s...
  29. W

    Quantum Most accurate modern physics book

    I have been plagued by modern physics and quantum mechanics books before that employ the traditional approach where they start from Photoelectric effect, Blackbody radiation, etc. (This is really not an issue but in fact illuminating since it shows how old QM developed) until you read about...
  30. Seven of Nine

    Intensity of Light using Quantum theory

    Homework Statement Approximately 4% of the intensity of light is reflected at a glass-air boundary. Classically one expects roughly 8% of light to be reflected from a thin glass plate (4% at the front and back boundary). Outline briefly what quantum theory predicts for a single photon instead of...
  31. D

    Mercury's orbit according to Classical VS Modern Physics

    Hello, I'm a high-school student and I was assigned to do this kind of a paper as a senior (one of the requirements of graduating is a short monograph on a subject of interest.) My topic includes an analysis of Mercury's orbit using Newton and Kepler's equations and comparing the predicted...
  32. egetunc

    Looking for a project for modern physics class

    For my modern physics course our group(3 people) need a project to build in 12 week,(so not short, 2-3hours work for each person per week) Our topics are: Relativity Waves and Particles I Waves and Particles II Bound States: Simple Cases Unbound States: Obstacles, Tunneling and Particle-Wave...
  33. Pushoam

    Ratio of energy densities of black body radiation

    Homework Statement Homework EquationsThe Attempt at a SolutionThe energy density is given as ## u = \frac { 8 \pi {\nu }^2}{c^3}~ \frac { h \nu} {e^{ \frac { h\nu}{k_B T}} – 1}.## EDIT : I put the constant C. ## \frac { u( 2 \nu) } {u(\nu)} = C \frac { {e^{ \frac { h\nu}{k_B T}} – 1}...
  34. Pushoam

    Compton Scattering: Solving for E with $\phi = 1/4\pi$

    Homework Statement Homework EquationsThe Attempt at a Solution ## \lambda' = 2 \lambda ## ## \lambda' - \lambda = \lambda = \frac { h} { mc} \cos{ \phi } ## Here, ## \phi = \frac { pi} 4 ## is the angle between photon's original line of motion and its line of motion after...
  35. B

    Part-Time Student: 300-Level Physics Classes

    I'm not if this is the right place for this, so mods can feel free to move this. I'm a part-time student going into my second semester of 300 level physics class. This past semester I oscillated between feeling just fine and questioning whether physics was right for me (usually around test...
  36. Pushoam

    Energy needed to remove both electrons from a He atom

    Homework Statement Homework EquationsThe Attempt at a Solution [/B] Both electrons are in 1s orbit. For taking out the second electron, I will have to put slightly more energy than 24.6eV. So, the energy required to remove both electrons should be slightly more than 49.2 eV. So, I...
  37. Pushoam

    De – Broglie wavelength of O_2

    Homework Statement Homework EquationsThe Attempt at a Solution [/B] De – Broglie wavelength of ## O_2 ## molecule is ## \lambda = \frac h p ## Assuming that the speed of molecule is small enough to take non – relativistic calculation, ## \frac {...
  38. Pushoam

    Doppler effect: calculate speed of a moving star

    Homework Statement Homework EquationsThe Attempt at a Solution When the source is not moving, ## \lambda = 6250 A ## ...(1) When the source is moving, ## \lambda ' = 6500 A ## ...(2) From (1) and (2), ## \lambda ' > \lambda ## ...(3) This means that the source is moving away from...
  39. Pushoam

    Change in the energy of photon due to recoil of the nucleus

    Homework Statement Homework EquationsThe Attempt at a Solution Since energy of photon is very low compared to the rest mass energy of the nucleus, I consider non – relativistic calculation. Conservation of linear momentum gives : momentum of nucleus = momentum of photon = p...(1)...
  40. Pushoam

    The amount of radioactive substance after 38 days

    Homework Statement Homework EquationsThe Attempt at a Solution Is there anyway to choose the correct option without solving it? ## \lambda = \frac { 0.693 } { t_{\frac 1 2}} ## [/B] ## N = N_0 e^{- 0.693 {\frac { t } { t_{\frac 1 2 }}}} ## ## N = 10.24 e^{- \frac { 0.693 * 38 } {...
  41. Pushoam

    Wavelength of em radiation of H - atom

    Homework Statement Homework EquationsThe Attempt at a Solution E = (13.6 – 3.4 = 10.2)eV = ## \frac {hc } { \lambda } ## =1.22 * 10^{-5} cm So, the correct option is (a). Is this correct?
  42. C

    B Speed of light and modern physics

    What will happen if something traveling faster than light is found?What effect will it have on modern physics?
  43. MARX

    BEISER MODERN PHYSICS Rotational Energy Level

    Homework Statement The rotational spectrum of HCl contains the following wavelengths: 12.03 10 5 m 9.60 10 5 m 8.04 10 5 m 6.89 10 5 m 6.04 10 5 m If the isotopes involved are 1H and 35Cl, find the distance between the hydrogen and chlorine nuclei in an HCl molecule. Homework Equations E...
  44. I

    Special Relativity: Traveling to Regulus

    Homework Statement A visit to Regulus is on my bucket list. However, it is 77 light years away. Assuming I will live only another 40 years, can I make it to Regulus? How fast would I have to travel (at constant speed) to get there in 40 years? Homework Equations t1 = t0...
  45. C

    Is modern physics as a course necessary for all future physicists?

    So I'm about to start my second year of college soon, I'm majoring in physics. I've noticed that some universities (places like Princeton, MIT, etc) don't have a course on modern physics, where a more superficial treatment is given to things like special relativity, quantum mechanics...
  46. D

    Intro Physics Top Modern Physics Books for Undergrad Students

    Does anyone know about some good modern physics books for an undergrad student? Not a textbook but just a simple paperback to give me an introduction to some typical topics discussed in a modern physics course. Thank you!
  47. peroAlex

    Special Relativity: Length Contraction Problem

    Hello! I have a small problem with a task professor gave us. I tried many options (you will see below) but I cannot seem to get the right solution. Any advice or guideline how to solve this would be really helpful. In advance I thank you for helping me. Homework Statement Our professor of...
  48. Kudox117

    Lorentz Transformations vs Galilean Transformation

    Homework Statement 2. The attempt at a solution 3. Relevant equations In the first problems of that book i was using the Galilean transformations where V1 = V2 + V But if i use that then V1 = 0.945 - 0.6 V1 = 0.345 Is not the same result, so I am confused. In this new problems we are...
  49. A

    Answer: Neutron Interference: Understanding Kinetic Energy

    Homework Statement the question details are given in the attachment Homework Equations momentum = √2mE where m is mass of neutron and E is its kinetic energy The Attempt at a Solution initially i accounted for the energy change during the path followed by the neutron but later i got...
  50. SunRay-dvsh

    A Why is the Matter wave analogous to photon and derived from it?

    The electromagnetic wave derivation uses the fact that charge enclosed is zero and it goes to obey plane wave equations. Lets say we were deriving a wave equation from maxwell's equations for electron wave motion, but we assume that charge enclosed is not zero, and come up with some...
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