# What is Doubts: Definition and 203 Discussions

Doubt is a mental state in which the mind remains suspended between two or more contradictory propositions, unable to be certain of any of them. Doubt on an emotional level is indecision between belief and disbelief. It may involve uncertainty, distrust or lack of conviction on certain facts, actions, motives, or decisions. Doubt can result in delaying or rejecting relevant action out of concern for mistakes or missed opportunities.

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1. ### Can Personal Interest Drive Mastery in Physics?

I've always been fascinated by physics but never had the opportunity to pursue it academically. That's why I'm here—to clarify the physics-related doubts and questions that have always intrigued me.
2. ### B Doubts about the definition of a linear system

hello I have doubts about linear system suppose that x is the input and y the output if x1 then y1 if x2 then y2 the system is linear if if (x1+x2) then (y1+y2) now, take a mass m you can write f = m*a however suppose that m changes with position m = m(x) above equations should be still...
3. ### Beam deflection and curvature radius formula doubts

Hi, I am working with leaf springs and studying the derivation of the formula for the deflection of such a structure. The derivation is shown here: My only doubt is how to obtain the following formula: $$\delta=\frac{L^{2}}{8R}$$ where: ##\delta## - deflection, ##L## - length of the beam...
4. ### I Doubts about Fourier transform of IR spectroscopy

I was studying a Michelson interferometer for infrared absorption in Fourier transform and I've found these two images (taken from https://pages.mtu.edu/~scarn/teaching/GE4250/ftir_lecture_slides.pdf ) representing an infrared monochromatic beam of light going into the interferometer and the...
5. ### MHB About non persistent (parallel and serial) http connections doubts-:

This figure is the one given in not my textbook mentioned in syllabus but the local author book that many teachers use to follow while checking exam papers. If you don’t write according to what is written in these books, they won’t even give you 0.001 marks. So I want to learn this figure rather...
6. ### I More doubts in perturbation theory

Townsend, quantum mechanics " In our earlier derivation we assumed that each unperturbed eigenstate ##\left|\varphi_{n}^{(0)}\right\rangle## turns smoothly into the exact eigenstate ##\left|\psi_{n}\right\rangle## as we turn on the perturbing Hamiltonian. However, if there are ##N## states ##...
7. ### B Sadi Carnot's Doubts: Exploring Universal Physics

Hello In his book published in 1830, Sadi Carnot expresses doubts as to the universality of his reasoning on gases. It's on page 89. Is it valid for liquids, solids? And he quotes in the text the freezing of water (increase in volume). What experiments or reflections allowed Rudolf Clausius to...
8. ### Doubts about the electric field created by a ring

I have the calculation of the electric field created by a ring of radius ##R## uniformly charged with a linear density of charge ##\lambda## at any point on the axis perpendicular to its surface (##z## axis), but I have some doubts about it. I'll leave you the calculation done first: In ##x##...
9. ### Doubts about deep drilling in metal with an HSS drill

hello my friends, the other day I read that the barrels of firearms before 1930 (the birth of gundrills) the barrels were forged from plates until they became a tube and later, they were made from steel bars that were drilled with welded HSS drill bits. Does anyone have experience with the deep...
10. ### Doubts on Exercise Wording: Energy Density & Poynting Vector

I have doubts about the wording of the exercise: (1) energy density is ##u=\varepsilon_0 (cB)^2## but since the question asks for mean energy density should I perhaps average over ##cos^2 (\omega t)## (there due to the ##B^2##) and thus use ##<u>=\frac{1}{2}\varepsilon_0 (cB)^2##? (2) it seems...
11. ### Engineering I have some doubts regarding AM Modulation

3) Suppose, V DSB-SC as follows: Are the following spectrums correct? The carrier frequencies are given as an example.
12. ### B Basic doubts in vector and multi variable calculus

If say we have a scalar function ##T(x,y,z)## (say the temperature in a room). then the rate at which T changes in a particular direction is given by the above equation) say You move in the ##Y##direction then ##T## does not change in the ##x## and ##z## directions hence ##dT = \frac{\partial...
13. ### B Solving Doubts about Simultaneity Exp. in Special Relativity

I'm reading about how the concept of simultaneity breaks down in special relativity. Here's the relevant paragraph: ----- Consider a photon source ##C_0## in a train car situated equidistant between detectors ##C_1## and ##C_2##. The source emits photons back to back. In a reference frame at...
14. ### I Doubts regarding atomic spectra of mono-electron species

I was studying about atomic spectra of mono-electron species and in the pic it describes the ##4## series (principal, sharp, diffuse and fundamental). However I'm a little confused by the formula.Here my doubts are: Thanks for reading. [1]: [2]...
15. ### Three doubts in a paragraph on the equilibrium of Incompressible fluids

These are the images from Sommerfeld’s Lectures on Theoretical Physics, Vol 2 chapter 2, section 6, Equilibrium of Incompressible Fluids. Image 1 Image 2 Doubt 1 : What does it mean for a force to act on a fluid volume? Force acts on a point, force may act on a surface but I’m unable to...
16. ### Doubts about the method of determining the elastic constant of a spring

Good afternoon,I am preparing a laboratory report on the study of the oscillations of a spring and the following questions have arisen:The script asks us to represent the mass against the squared period, in this case, the slope will correspond to the spring constant divided by 4Π^2 and the...
17. ### I Understanding the Absence of Rabi Oscillations in the Interaction Picture

When working on the interaction picture you can show that in a certain rotating frame the Hamiltonian of a 2-level system (for example) becomes uncoupled. This implies that in such frame there are no Rabi oscillations or other dynamical phenomena, this seems weird to me and I would like to know...
18. ### Why do I feel centrifugal acceleration when standing on a revolving ball?

If a "stand" on the ball, I would feel a centrifugal force, which would be pulling me out of the circle. But in the equation of centrifugal force we have ##\vec r##, which is the vector that goes from the centre of the non inertial frame to the body in motion. But if I'm on the ball, my system...
19. ### Doubts on the sign of acceleration

What should I do? Because I have two possibilities. I have ##0=5+at## so ##-5/t =a##. But then I can also say that the acceleration is a negative because it is stopping, so I can write it like ##0=5-kt## and then ##5/t =k##
20. ### I have two doubts in this equilibrant problem (resultant force)

Two forces are pushing an object along the ground. One force is 10 N [W] and the other is 8.0 N. Sketch a diagram showing the equilibrant of these two forces, and determine the equilibrant. Ans) Calculate the equilibrant... C2 = a2 + b2 = 102 + 82 c = 13 NDiagram: tanΘ = opp/adj = 10 / 8...
21. ### A Doubts in a lattice translation example

I have two question about a exemple given in the Sakurai's quantum mechanics book, section 4.3. Let's consider an electron in a periodic potential ##V(x + a) = V(x)##, that has the form of a wave. We will take the potential to go to infinity between two latteces sites, such that its form change...
22. ### Doubts with the MCNP software for my thesis

Hello, it's a privilege to enter in this forum. My name is Geovanny, I'm from Mexico and I'm a student from the Autonomous Yucatan University. I'm studying in my last semester of Physical Engineering and i have some doubts about de MCNP software. One of those is the next message that VISEDX...
23. ### Doubts about the mechanics of walking

Hello :smile: When we are walking, exist, basically, three forces on us foot.(gravity, normal and friction forces). Considering that the frictional force is in static regime, the resulting force is 0. Theoretically, there is no relative movement between the foot and the floor. So my doubts: How...
24. ### B Doubts in Calculating Nuclear Reactions

I am not talking about the reactions of simple atoms in chemistry, I am speaking, for example deuterium, heavy water, isotopes of hydrogen, oxygen, carbon, etc.I would like to know how to calculate when two atoms merge, to know mathematically what atom will form, example deuterium + deuterium =...
25. ### This teacher has doubts that microwaved food is safe

What do you think? Why would he think microwaved food would be dangerous? He doesn't really explain why...Most of the time that I heard microwaved food was dangerous was from crackpots that also thinks we will all get fried by 5g wifi... this is a teacher though kind of concerning Starts at...
26. ### Basic doubts about measurements and fitting

Homework Statement Let's say I'm doing a experiment in order to measure a resistance of a single resistor of 200 ohm by its V against I graph, where V is the voltage in the resistor's terminal given by and voltmeter and I the current of the circuit, given by and ammeter. The angular coefficient...
27. ### B Light Propagation: Doubts Answered Here

Hello There:woot:, I have basic doubt about light propagation .So I'm hoping to get some help here. The problem is ...Let us assume two frames, 'MOVING FRAME'[one moving with a certain velocity(constant)] and 'REST FRAME'[one wrt to which the first frame is moving]. If now moving frame emits a...
28. ### B Normal Force on Extended Block: Physics Explained

Suppose there is an extended block lying on a frictionless surface. The surface will exert a normal force on block. Will the normal force act at one particular point on the block, or will it act along the entire length of block?
29. Q

### Electrical displacement: doubts

Hi. Maybe you can help me. I am reading history of physics, especially the moment when Maxwell completes Ampere's law with the displacement current. My doubts are about propagation in a vacuum. 1. Can I say that in an electromagnetic wave there are several undulating fields, one of them the...
30. ### Forces on Dielectrics: Understanding Griffith's Equations

Forces on dielectrics I found difficulty in understanding this topic from Griffith. Here, while calculating F, in eqn. 4.61 , Griffith doesn't bother about energy stored in fringing field. So, even if I assume that there is no fringing field, then following the above procedure, I can say...
31. ### Doubts regarding basic chemistry concepts

Doubts regarding the law of reciprocal proportions: What i have understood by reading the definition is that the ratio of the masses in which two elements A and B combine with a fixed mass of a third element C, will be a whole number multiple of the ratio of the masses in which A and B combine...
32. ### Doubts Arising from Clausius' Inequality and the Second Law

I began reading Mehran Kardar's Statistical Physics of Particles and about halfway through the first chapter, there was a discussion on the second law of thermodynamics. He makes no mention of the old tenet that 'the total entropy in the universe must always increase' (I'll refer to this as the...
33. ### B Some doubts about functions.... (changing the independent variable from time to position)

Functions are pretty simple things , they just express a relationship between two different quantities How do i express this function in terms of y(x) = something ?
34. ### MHB Few beginner doubts about differential equations ?

I was trying to picture the third derivative of something Then i came across these ... What does displacement mean? The variable x is often used to represent the horizontal position. The variable y is often used to represent the vertical position Displacement=Delta x=xf-x0xf refers to the...
35. ### B Some doubts about these differentiation steps

First of all there is an equation Then there is the derivative Then there is a point slope formula to find the equation of the tangent line Point slope formula to obtain the tangent line . y=3a2(x-a)+a3 Then Plug in the x coordinate into the derivative to get the slope f'(1) = 3(1)2 f'(1) = 3...
36. ### MHB Calculus & Diff. Eqn: Beginner Qs on Function, Derivative & Gradient

I have some beginner doubts about Calculus and Differential equations . Is a function always a curve ? Doesn't a function already has a slope ? d/dx of a function gives the gradient of the curve between two points ? The derivative ,d/dx ,The gradient , is the rate of change of a...
37. ### Doubts regarding solubility product problem

As I am also attaching solution along with the problem there is no point in posting this thread in homework forums . In the following question (solution is also there) https://s29.postimg.org/omlnt73lz/IMG_20170407_090748.jpg https://s18.postimg.org/hsuxm5uvt/IMG_20170407_090805.jpg why are we...
38. ### Physics problem doubts - Circuits

Homework Statement [/B] 2. Homework Equations Req= R1 + R2...Rn for resistors in series. Req= (1/R1 + 1/R2 +... 1/Rn)^(-1) for resistors in paralel And Ohm's Rules for circuits The Attempt at a Solution I did manage to solve it by using R3= 0 and thus finding R1= 2000 by using Ohm's Rules...
39. ### I Photoelectric Effect: quantum energy doubts

Hey, I've being studying the Photoelectric effect, I think I understand it superficially. One thing that has been bugging me is this: "Given that it is possible to move electrons with light and given that the energy in a beam of light is related to its intensity, classical physics would predict...
40. ### I Yes, thank you for explaining it to me. I have a much better understanding now.

Hi, I am a physics student and i was asked to answer some questions about Hydrogen atom wavefunctions. I hope you can help me (sorry for my english, is not my motherlanguage, i will try to explain myself properly) 1. In order to find hamiltonian eigenfunctions of Hydrogen atom, we make then be...

Hello world. I am currently a junior at a very high powered physics school that u transferred to. I am majoring in physics and have been planning on going to grad school. However, lately I've been having doubts about my major. I came here from another school in the UT system. Everything was fine...
42. ### I want to clear my doubts (friction and work)

i read in a book-'work is done when a force moves its point of application.this involves movement of the object on which force acts and movement of the force itself.' when this is true ,then why is the work done by friction on pencil zero when pencil makes a circle on a page ? i assume that tip...
43. ### Other I wanna become a theoretical physicist(questions and doubts)

I want to become a theoretical physicist and work on string theory and quantum mechanics and stuff like that but I don't know how. Should I go to a high rated school or just the oridinary? I don't need to get paid a lot but I would like to get atleast the average(not sure what that is) but since...
44. ### Doubts regarding Electromagnetic fields

I read in a book that Electromagnetic fields propagate at speed of light and carry energy and momentum. Let's take electric field for example. Electric field is none other than a force per unit coulomb.So 1.How could a force(here field) move as force has no property of moving as force causes...
45. ### I Doubts on wavefunction conditions

I'm facing some difficulties in using "boundary conditions" in a simple wavefunction. The wavefunction I'm considering is $$\xi(x,t)=A sin (k x \pm \omega t +\psi)$$ The minus or plus are for progressive or regressive waves. The indipendent parameters are 4: ##A##, ##k##, ##\omega##, ##\psi##...
46. ### Solving Calculus Doubts: My Attempt

While studying energy conservation on Morin I found this explanation about the work-energy theorem for a system. Using Koenig theorem $$\Delta K_\textrm{system}=\Delta K +\Delta K_\textrm{internal}$$ so we have I've got two main question on that: Why are only external forces considered for...
The wave equation is $$y = A\sin (\omega t \pm kx \pm \phi_i)$$ What exactly is kx? Why it is needed? Why can't we directly represent wave as we represent SHM - $$y = A\sin (\omega t + \phi)$$ I even read that between the waves there is a phase difference of π - $$y = A\sin (\omega t - kx)$$ and...