What is Doubt: Definition and 591 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. Gh0stS3C

    Doubt regarding conversion of eV to V

    So I know exactly how to solve this question with the relevant equations. However problem I ran into was how I substitute for K.E (Kinetic Energy). I asked one of my teachers for help. She said that since the voltage applied stops the experiment, it is equivalent to the energy of the electron...
  2. C

    Can I simplify this RLC circuit problem using a different method?

    Hello, I have been thinking about this problem for a few hours, and I do not understand how I should proceed to solve it correctly. Section a is very simple, just substitute in the expression that gives us the values of L and C that the statement gives us. However, when I get to section b, I...
  3. LCSphysicist

    A doubt about force directions

    Exercise like this: I think that the friction force can assume two direction, up and down, but how can i know the direction of the force? I want to say, i don't even know which mass is greater to say i the block will upward or downward. that is the doubt. That is the correct forces directions...
  4. ANSAN

    Geartrain Doubt.... How to select the number of teeth given other specifications

    Hai all, I need to get to know how a Gear pair teeth numbers are selected. Details : Power = 300KW, N1=2950, N2=816.5 , i=3.62, Helix angle = 35deg, Pressure angle = 20deg. I need to know how to select a Gear pair teeth for this input? Knowing a gear set should have common Module to transmit...
  5. R

    A doubt on total differentials

    Please refer to the images and my handwritten note(i tried my best handwriting) for the question
  6. R

    B Another doubt I had while reading Feynman Lectures

    "The “stage” on which the universe goes is the three-dimensional space of geometry, as described by Euclid, and things change in a medium called time." -Feynman Lectures Do the 1st two lines mean that the thing in which everything moves around is the 3 dimensional space...am i interpreting it...
  7. R

    B Can someone answer this doubt I have on Set theory?

    "The fact that the above eleven properties are satisfied is often expressed by saying that the real numbers form a field with respect to the usual addition and multiplication operations." -what do these lines mean? in particular the line "form a field with respect to"? is it something like...
  8. R

    B A doubt on the fundamental unit of charge

    "a charge smaller than e has not been found. if one determines the amount of charge on any charged body like a charged sphere or charged drop) or any charged particle (like positron, a-particle) or any ion, then its charge is always found to be an integral multiple of e, i.e., e,3e; 4e,... No...
  9. R

    A doubt on Electrostatics -- An electrified rod attracting light objects

    "When electrified rods are brought near light objects, a similar effect takes place. The rods induce opposite charges on the near surfaces of the objects and similar charges move to the farther side of the object." -from a high school physics book. NCERT Class 12th part 1 to be precise. can...
  10. R

    B A doubt on Rutherford's Scattering experiment

    Please refer to the image attached for the question.thanks.
  11. R

    B A doubt on Thomson's Experiments to determine the value of e / m_e

    By carrying out accurate measurements on the amount of deflections observed by the electrons on the electric field strength or magnetic field strength, Thomson was able to determine the value of e/me as... e/me = 1.75 10^11 C kg^-1 would this be a correct understanding of this para- "This para...
  12. R

    B A simple doubt on functions.

    Why do we define functions as only as only those graphs which have only one y value for each x value. for eg. we don't say that a circle is a graph of a function,because its graph would have two y values for same x values. what i mean to ask is why not call anything that takes a input and gives...
  13. J

    I Why does mass matter in Rutherford's experiment?

    Here it goes. I'm reading some notes on the Rutherford (gold foil) experiment and they first state what one should expect if the atom model was like the one described by Thomson (plumb pudding model). In order to somehow predict what the deviation should be when throwing alpha particles towards...
  14. G

    A S-matrix expansion and Wick's theorem

    My question arises when we expand the S-matrix using Wick's theorem, there we need to compute time-ordered products, but is not the same to compute $$T\{\bar{\psi}(x_1)\gamma^\mu \psi(x_1) A_\mu(x_1)\}$$ or $$T\{:\bar{\psi}(x_1)\gamma^\mu \psi(x_1) A_\mu(x_1):\}$$ While the second one is simply...
  15. I

    Doubt about solving a simple quadratic equation

    I was thinking of this simple equation here, ## x^2 = 4##. Many students present the solution as follows. $$ x^2 = 4 $$ $$ \therefore x = \sqrt{4} = \pm 2 $$ Now, even though the final answer is correct, there is a mistake in arriving at the solution. Square root symbol means that we have to...
  16. C

    Doubt about the 1st Law of Maxwell

    Good afternoon, My question concerns Maxwell's first law. Knowing the formula of the electric field created by a uniformly charged disk, we calculate its divergence and evaluate it at one point, it does not give us zero, as it should be because the volumetric density of charge is zero, why does...
  17. W

    A Doubt about Energy Condition in Wormhole: Integral Along Null Geodesic

    I am now reading this paperhttps://arxiv.org/pdf/gr-qc/0405103.pdf, which is related to the energy condition in wormhole. Nevertheless, I got a problem in Eq.(6), which derives from so-called ANEC in Eq.(2): $$\int^{\lambda2}_{\lambda1}T_{ij}k^{i}k^{j}d\lambda$$ And I apply the worm hole space...
  18. W

    A Time Measurement in MT Traversable Wormholes - Help Needed

    I am reading this article now :http://www.cmp.caltech.edu/refael/league/thorne-morris.pdf. And i am a little bit confused about the Eq.(38a)and Eq.(38b), which means the time measured by traverller and people in the sataion, and I just think the time measured by traveller should be his proper...
  19. C

    Doubt about Jacobi's diagonalization method

    Good Morning, I am using the Jacobi diagonalization method for symmetric matrices and I have realized that as the number of iterations progresses, the speed with which the larger element (in absolute value) outside the diagonal of the diagonal becomes smaller Matrices are increasing (graphical...
  20. Like Tony Stark

    Understanding Pseudo-Forces in Non-Inertial Frames

    I know that, if my ##X## axis is aligned with the arm, there is friction pointing to ##O## and the ##x## component of the weight. Then, on the ##Y## axis, there is the normal force and the ##y## component of the weight. Supposing that I am situated on the arm (non inertial frame), where is the...
  21. warhammer

    A Conceptual doubt in a problem on Wien's Law

    Given λ=700nm, we use the equation mentioned above and find the Temperature to be 4140K. However, my doubt is that the wavelength specified to be used above is a maximum and I'm not sure if the answer is (a) or (d) considering that the latter is a range of the temperature.
  22. Manasan3010

    Is an answer possible - Conditional Probability

    I am a noob to this topic so correct me If I made any silly mistake. By plugging in the values I managed to get p(abc)=0.75*0.9*p(c|ab) Here How can I find p(c|ab)? Is this question unsolvable or can I derive it? I also want to know what is meant by p(abc) in literary terms. I also created a...
  23. Benjamin_harsh

    Please explain this doubt about a block sliding question

    Sol: ##Mg.sinθ - μMg.cosθ = ma## ##a = g.sinθ - μg.cosθ## Now ##S = ut + \large\frac{1}{2}\normalsize at^{2}## but ##u = 0## ##t = \large\sqrt\frac{2s}{a} = \sqrt\frac {2s}{gcosθ(tanθ- μ)}## My questions: What is the meaning of " PQ = s" in the question? How ##t = \large\sqrt\frac{2s}{a}...
  24. G

    Where is the Error in My Derivation of the Magnetic Field Equation?

    As I said my goal is to derive the equation ##\tilde{B}^k(\vec{q})=-i\varepsilon^{ijk}q^i\tilde{A}^j_{cl}(\vec{q})## As far as I know, the magnetic field is defined using the potential as ##\vec{B}=\vec{\nabla}\times\vec{A}## Then in equation 6.6 they define ##A^\mu(x)=\int...
  25. K

    Doubt about calculating the solubility of lamivudine (3TC)

    Hi, I have a doubt about calculating the solubility of lamivudine (3TC). Suppose you have an excess of free base lamivudine (B) in solution. An equilibrium is generated between B in the aqueous phase and B in the solid phase, i.e. in solution and the base body. As we acidify the pH by...
  26. C

    Small doubt regarding electric charge

    Good morning I'm no expert in classical physics, so I have one doubt. If I have a body with mass M, and I charge it electrically with x C (Coulombs), will its mass remain the same, or will it change (in which amount)? Can you help me in the case of a ball, let's say, with 1.5 Kg charged with...
  27. B

    I Basic doubt on chain rule in DAlemberts soln to wave equation

    In D Alembert's soln to wave equation two new variables are defined ##\xi## = x - vt ##\eta## = x + vt x is therefore a function of ##\xi## , ##\eta## , v and t. For fixed phase speed, v and given instant of time, x is a function of ##\xi## and ##\eta##. Therefore partial derivative of x w.r.t...
  28. A

    A Doubt about a time convolution master equation

    I study of interaction between a system with a reservoir considering a weak coupling between them. I consider a bosonic bath, the initial state are separable and the operator of interaction between the system and bath is linear in the displacements of the oscillators. . In the book "Quantum...
  29. Kaguro

    I Doubt about a probability density

    I was trying a problem from Griffith's Introduction to QM. The problem was: The needle on a broken car speedometer is free to swing, and bounces perfectly off the pins at either end, so that if you give it a flick it is equally likely to come to rest at any angle between 0 to ##\pi##. a)Find...
  30. A

    B A little logical doubt on Hawking radiation

    Summary: As hawking radiation is based on quantum fluctuations, can they cancel out each other due to equal probabilities of a particle remaining in or drifting away? I recently learned how hawking radiation actually works. It is based on quantum fluctuations which happen randomly in space...
  31. A

    Doubt about a unit vector in toroidal coordinates

    The system considers a torus that has a wire wrapped around it, through which a current flows. In this way, a field originates in the phi direction. The direction of current is "theta" in the spherical coordinate system but in toroidal system, in several book shows that the electrical current...
  32. J

    B Proietti 2019 experiment: Doubt in measuring A1(B1)

    Hi everyone! Sorry for the bad english! Paper: https://arxiv.org/abs/1902.05080 I guess I understood the experiment until the moment Alice and Bob chooses to measure A0(B0) or A1(B1). I guess it's kind of straightforward that without a bell state measurement with photon alfa(beta) and photon...
  33. L

    I Doubt in the quantum harmonic oscillator

    I was reviewing the harmonic oscillator with Sakurai. Using the annihilation and the creation operators ##a## and ##a^{\dagger}##, and the number operator ##N = a^{\dagger}a##, with ##N |n \rangle = n | n \rangle##, he showed that ##a | n \rangle## is an eigenstate of ##N## with eigenvalue ##n -...
  34. Abhishek11235

    I Doubt in the Application of a Pseudo Force

    Here is the problem in Morin. In this problem he takes the person on carousel as origin. Accordingly,when he begins to apply Newton's Law of motion on himself,by the equation of pseudo force,since he is motionless in his own frame,his own acceleration is 0. Further in his own frame he has 0...
  35. ubergewehr273

    B Doubt on an EM problem regarding gauss law

    There's this problem 2.18 in the book "Introduction to electrodynamics" by Griffith. The problem says the following, "Two spheres, each of radius R and carrying uniform charge densities ##+\rho## and ##-\rho##, respectively, are placed so that they partially overlap (Image_01). Call the vector...
  36. jishnu

    Doubt regarding a basic Python operator

    Hi everyone, I am beginner in python programming. So many doubts are being generted in the learing process Can anyone please explain me how the bitwise NOT (~) operator actually works on values. I have attached a screen short of my textbook (unofficial) with this post and I am confused how...
  37. E

    Does work have the same impact on entropy change as heat?

    1. Homework Statement if a rigid adiabatic container has a fan inside that provides 15000 j of work to an ideal gas inside the container, does the change in entropy would be the same as if 15000 j of heat are provided to the same rigid container (removing the insulation)?2. Relevant equations...
  38. Logic hunter

    Why do gases occupy different volumes in eudiometry?

    I know how to solve problems of eudiometery but i don't understand a really basic thing ie how come gases occupy different volumes in an eudiometery tube. (For eg: 15ml of hydrocarbons with 320ml other gases). Gases occupy entire volume of the container, right. So shouldn't all gases occupy the...
  39. C

    I A little doubt regarding specific angular momentum

    Good afternoon I just have this little doubt: imagine the osculating orbit of Mars changing slowly in its elements along the centuries. The semi major axis changes, the period, etc. Is the specific angular momentum allways equal in all the osculating orbits Mars has in those centuries? Or does...
  40. Celso

    Power waste (conceptual doubt)

    I'm currently in a undergrad level course of eletromagnetism and my professor found it useful to remember quickly of some relationships that we see in high scool, among them power waste. I got the formulas, since they're simple and are direct derivated from the definitions of electric current...
  41. Kaguro

    I Solving Lorentz Contraction Question: What went Wrong?

    Hello all. I am having some small trouble with applying the lorentz transformations to calculate lorentz contraction. Here's what I did: Let O be the rest system and O' be the system moving with velocity v w.r.t O along x axis. Consider a rod lying in the O' system with ends x1' and x2'...
  42. F

    Doubt on an exercise involving Torque

    Homework Statement In the following figure we have an homogeneous L-shaped bar that has weight 120N. It's articulated without friction at point A. It's vertical part has length 1m and its horizontal part has length 3m. Find the intensity of F that maintains the bar in equilibrium. 2 ...
  43. V

    Hybridisation Doubt: When Does it Take Place and When Not?

    There is an example given in my textbook showing the structure of BF3. In it, they have hybridised the orbitals of B to sp2, but not of F. It's written sp2-p overlapping. Why isn't flourine also hybridised, seeing it has 3 lone pairs and 1 bond pair, it could have sp3 hybridisation? Also, in...
  44. V

    Why is the normal reaction force zero in the absence of any external force?

    Homework Statement My question is not a homework problem. I am having difficulty in understanding the concept oof contact forces. Homework Equations What I don't understand is that when two bodies A and B are in contact and left on a frictionless surface, they apply normal reactions on each...
  45. david3305

    Finding x in Parallel Lines Geometry Problem

    Homework Statement Find x. L1 and L2 are parallel choices: a)2°40' b)2°30' c)2°45' d)2°15' e)2°20' Homework Equations Σleft∠ = Σright∠ The Attempt at a Solution 2x+1+4x-1+4x-1 = 2x-1+2x+4+3x+2 10x-1=7x+5 3x=6 x=2° Not sure how the answers include minutes ' Maybe I'm overlooking something?
  46. Kaguro

    Understanding Polar Vectors on a Circle

    Homework Statement What is the sum of position vectors of all points on a circle? Don't use Cartesian system. Homework Equations Sum vector $$\vec s = \int_{\theta=0}^{\theta=2{\pi}}\int_{r=0}^{r=R} \, \,\vec P \, dr d\theta$$ where $$\vec P$$ is the position vector. The Attempt at a...
  47. Kaguro

    I Doubt regarding derivation of Lorentz Transformations.

    I have just started learning the Special Theory of Relativity. While deriving, I am facing some problems. I obviously have made some kind of mistake while using the equations... What is wrong if I don't use the time transformation equation in Event #2?
  48. D

    Sedimentation Doubt: Correct Me if I'm Wrong

    Homework Statement I think the second notes is wrong . I think when the settling velocity is greater than overflow rate , then the particles should be removed easily ... However , in the second notes , the author stated that if vs > vo , the particle remained in the tank ... Homework...
  49. A

    A level physics doubt about a Diffraction grating

    Homework Statement Monochromatic light of wavelength 690nm passes through a diffraction grating with 300 lines per mm, producing a series of maxima on a screen. What is the greatest number of maximas that can be observed? A) 4 B) 5 C) 8 D) 9 Homework Equations n*wavelength = d*sin x The...
  50. Allen_Wolf

    B Can Entanglement be Used for Faster-than-Light Communication?

    Let us say we have an entangled pair of photons with opposite spin, which we want to use to transmit information at a speed greater than the speed of light. One of the spins could be assigned as YES (1) and the other as NO (0). We keep one photon and send the other to the receiver. In case out...
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