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. V

    Doubt about Implicit differentiation

    Hi all, I was reading a paper in which implicit differentiation was used as follows x \in R, \lambda \in R Given G(x,\lambda) = 0 \frac{\partial G(x,\lambda)}{\partial x} \frac{\partial x}{\partial \lambda} + \frac{\partial G(x,\lambda)}{\partial \lambda} = 0 My doubt is...
  2. P

    Doubt in chemical equilibrium question.

    Homework Statement For the chemical equilibrium N_{2(g)} + O_{2(g)} \rightleftharpoons 2NO_{(g)} , the following values were found for the constant Kc (chemical equilibrium constant), at the indicated temperatures: (The table is attached as an image) Table in text format: Temperature (K)...
  3. K

    Pentavalent Elements & Doping Semiconductors: Why Not 6 Valence Electrons?

    Doping doubt... Why pentavalent elements are used in doping semiconductors why not an element with 6 valence electrons?
  4. D

    Why Does the Same Current Flow Through Every Segment of a Wire?

    Curent Electricity Doubt! PLEASE HELP! Homework Statement I did not understand one thing.. If it is given that a wire has a current 'i', then why do we say (in applications of laws such as biot savart law) that the current in a small element of the wire is also 'i', that is the same current...
  5. I

    What do Rcm and Rcmob represent in this fluid mechanics problem?

    Q2. An incompressible fluid with density ρ is in a horizontal test tube of inner cross-sectional area A. The test tube spins in a horizontal circle in an ultracentrifuge at an angular speed ω. Gravitational forces are negligible. Consider a volume element of the fluid of area A and thickness dr'...
  6. A

    A doubt on self inductance and mutual inductance

    i am having a doubt that when we find a expression for mutual inductance we say that flux change in primary coil induces emf in secondary coil. but why change in flux doesn't induce any current in primary coil also.
  7. Y

    A thought experiment doubt on General Relativity.

    I was reading a chapter on "General Relativity" a few days ago. (I was reading Arthur Beiser: Modern Physics)I found it very hard to digest the relation between the "Equivalence Priciple" and "The General Theory of relativity".The equivalence relation states that "An observer in a uniformly...
  8. V

    Accumulator Battery Internal Resistance & Charger Potential: A Doubt

    This is in continuation to https://www.physicsforums.com/showthread.php?t=330495 The question that initiated my doubt reads this -- " the internal resistance of an accumulator battery of emf 6V is 10 Ohm when fully discharged . as battery gets charged up , its internal resistance drops to 1...
  9. V

    Mechanics doubt in Newton's Law of Motion.

    Question-1. An engine of mass 105 tonnes is coupled to and pulls a carriage of mass 30 tonnes.The resistance to the motion of the engine is 1/100th of its weight.The resistance to the motion of the carriage is 1/150th of its weight.If the tractive force exerted by the engine is 25750 Newton.The...
  10. H

    Density Matrix Doubt: Can Coherance Be Zero?

    In a density matrix, can some coherances (off diagonal terms) be zero while the diagonal terms(populations) aren't? I am confused because rhoij=Ci*Cj'. How can coherance be zero if Ci and Cj aren't?
  11. Y

    Max232 IC Function, TXD & RXD, & Capacitors Explained

    Can anyone please tell me the function of the IC Max232 in a microcontroller board. Is it only necessary for serial programming. If I'm programming my board via parallel port, then do I require this IC? Why? What is TXD and RXD and what are their functions. Also why so many capacitors?
  12. A

    Doubt About D0 Branes: Point Particle & String Theory

    As far as I know a D0 brane is same as a point particle. If that is true then its presence in string theory would go against the very philosophy on which string theory is based (due to presence of 0-dimensional objects). Is my understanding correct? Also it seems to me that D0-D0 brane...
  13. W

    Can a Force of Gravitation Be Considered Conservative?

    I was watching 18.02 now and Denis Aurox, the prof. who is lecturing, mentioned that for a force to be conservative, not only was it necessary for its curl = 0 but also that F is defined and differentiable everywhere. He then went on to give the example y<i> + x<j>/x^2 + y ^2 will not be a...
  14. A

    Fortran Fortran Program Doubt: Plotting DST Index Values

    i have written a program to plot dst index values using fortran + pgplot, read the input as formatted input when I'm trying to plot the data points are not plotted correctly. k = 0 do i = isdt, iedt --------------start date to end date do j = 1,24...
  15. I

    Solving 82C55 Doubt: Usage & Examples

    I have a basic doubt about the usage pf 82C55. Wanted to know when exactly it is used. Eg: For a keyboard you have to use a 82C55 but for a LCD it is not necessary. So when exactly do we use it??
  16. A

    Doubt regarding Force exerted by a magnetic field on a moving charge

    a charged particle ( say 'q' ) moving with velocity 'V' in a region containing a magnetic field 'B' experiences a force 'F' given by: F = q(VxB) when V = 0, then force = 0 my doubt is, is this velocity relative to the magnetic field ? ( i.e. when the velocity relative to the...
  17. J

    Dealing with Doubt: How to Motivate Yourself Despite Insecurity

    This is kind of an odd post. To be honest, I don't really expect to see many responses, but I'm going to post it anyway. Back when I first started getting my degree, I wanted to prove something to myself. I had some self-esteem issues, a bit of an inferiority complex. I just needed to prove...
  18. S

    Solving Steering Related Doubt - Physics Problem

    Consider this situation. A non-rotating wheel is cruising through space such that its velocity vector is at some angle to the wheel plane. (Like when a car slides through ice when the driver turns the steering wheel). When its base touches a surface with friction, it takes a turn and its new...
  19. P

    Fundamental doubt in Thermodynamics

    in Thermodynamics, in a book i have read that during expansion of a gas(system), W(on system by surroundings)=-ve..They have proved it using W=-force(external)*displacement. They are saying as displacement is positive and force is always considered as positive, W=-ve. But, how did they determine...
  20. N

    Why is there a doubt in Coulomb's formula?

    Coulomb's formula states that the force of attraction between two electrically charged bodies is k(q1*q2/d^2), where k is 9*10^9 Nm^2/C^2. However, I have a doubt regarding this. We know that like charges repel and unlike charges attract. Let us take the case of like charges first. If both q1...
  21. K

    Why are some Maxwell relations written in reverse order?

    In thermodynamics, we always need to use exact differential relations to find the so called Maxwell relations. For a function of x and y, z=z(x,y) if dz = M(x,y)dx + N(x, y)dy the complete conditon for above equation to be hold is \frac{\partial M}{\partial y} = \frac{\partial...
  22. S

    Doubt regarding Length Contraction's derivation

    I have a doubt regarding the proof of Length Contraction. The proof of length contraction formula goes as follows: You choose a frame S (as shown in figure 1), suppose w.r.t. S, AB is moving with velocity v. Length of AB is L in AB frame and L1 in S frame. At t=0, a light pulse (shown with...
  23. V

    [Thermodynamics] Doubt about the relation between internal and external work

    Hello, while studying thermodynamics I was wondering why, in a system where the pression is not univocally determined (for example in irreversible trasformations), to measure the total work of the trasformation, we use to consider only the external forces. I mean, this sounds conceptually right...
  24. S

    Path Integral Doubt: How Did Shankar Deduce S/h>pi?

    I just read the chapter in Shankar regarding path integrals (the 8th) I didnt quite get how he deduced that destructive interference in the summation sets in after S/h>pi.(This is the first section itself) I couldn't find reference to such a thing elsewhere.
  25. P

    What Does Normal to the Reference Surface Mean in Love's Hypothesis?

    Doubt in Love's hypothesis... Please help... "Normal to the reference surface of the beam remain normal to it and undergo no change in length during deformation" What does this mean? please help...
  26. I

    Rotational doubt (also momentum)

    If a ball collides elastically with a stick at a point other than its centre of mass, then can we use coefficient of restitution is one or do we have to use initial kinetic energy = final kinetic energy?? If we can't use "coefficient of restitution is one" then why?
  27. T

    Any doubt to Emergent properties?

    Is there any doubt in the scientific community to the theory of emergent properties? I am of the opinion that they surely exist. In fact even today's fundamental particles might be an emergent property of something more fundamental. All of stat mech is a study of emergent properties, not to...
  28. S

    Will a Ball Stop in a Frictionless, Airless Tube?

    Hey i have a doubt . i have not tried this experiment but i wanted to know what would happen. If we take a tube bending at the end and joining to a 5 km long pipe which is frictionless (assume) and there is no air to offer air resistance . So when i start rolling the ball will it stop or not ...
  29. S

    Regarding signed dihedral angle doubt

    Hi to all.. I am doing Phd in bioinformatics, having little knowledge abt maths.. I have calculated Phi Psi angles(dihedral angle)between two planes... But the thing is i didnt get proper sign for my result(may be + or -). I used following formulae for calculate the dihedral angle between...
  30. I

    A strange fact as well as big doubt

    We know x^2 = x*x*x*x... x times If we differentiate both sides with respect to x, we have 2x=1+1+1+... x times i.e. 2x=x i.e 1=2 How is it possible or am i making a mistake? Please helpp!
  31. C

    Ionisation chamber - doubt about current nature and residue

    Homework Statement This is from Advanced Physics by Adams and Allday, section 8, practice exam questions, question 25. An α-source with an activity of 150 kBq is placed in a metal can. A 100 V d.c. source and a 109 Ώ resistor are connected in series to the can and the source. This...
  32. M

    Quick doubt on organic nomeclature

    Hi When naming organic compounds, hydrocarbons for example, it's very common to have several radicals of the same group attached to the 'main' carbon line. So for example, pentane, with 5 carbons in a row. Suppose we add 2 methyl to it, one on carbon 2 and one or carbon 3. We'd then have to...
  33. S

    Why Did the Michelson-Morley Experiment Assume Aether Has a Constant Velocity?

    can sm1 tell me why in the michelson morley experiment aeteher is assumed to have a unidorectional constant velocity ?? thankyou so much
  34. N

    Understanding Simultaneity in Special Relativity

    Hi everyone! I am new here. I like physics and so I am trying to understand a few things. I think I understood the Newton physics. Now I am reading about relativity. I began wiht special relativity. I just learn the two postulates. I think I can accept them without problems. I also read...
  35. G

    Fraunhofer Diffraction Doubt

    The relation between the angles for which the minima occurs for a Fraunhofer diffraction(parallel rays, large separation between screen and slit) is derived by using the destructive interference criterion. Why isn't there any mention of the criterion for maxima? The results obtained from the...
  36. H

    What is the largest angle for sin and tan to agree within 2 significant figures?

    For small angles theta, the numerical value of sin theta is approximately the same as the numerical value of tan theta.Find the largest angle for which sine and tangent agree to within two significant figures.
  37. P

    Is \(\frac{\partial T}{\partial q} = 0\) Always True in Classical Mechanics?

    is it necessarily true that we have \frac{\partial T}{\partial q}=0?
  38. N

    Understanding Simultaneity in Relativity: Common Doubts Addressed

    Hi everyone, I got interested in physics recently and started reading a book called "relativity simply explained " by martin gardener. when i was going through the book i got some doubts in relativity of simultaneity. my problem is described below o>>> ---------------------------<< 0...
  39. P

    Classical Mech doubt 4m Goldstein

    Can someone Prove the thing in bold letters?
  40. V

    Doubt about NMOS Transistor in Microcap: Varunag

    I was making a model of a NMOS transistor in Microcap. It was part of an assignment. I was supposed to make graph with changing value of V_{BS}. But after a certain value of V_{BS}, I got negative current. It came to my mind it is not possible. But, I couldn't think of a reason instantly, as to...
  41. P

    Understanding Constraint Forces in Mechanics

    in the "derivation" of 'principle of vitual work' Goldstein started with this he wrote the force F acting on each particle as the sum of F_{a} (Force applied) and F_{i}(Constraint force) ok i have some three queries 1)What are constraint forces? 2)Are all internal forces constraint forces 3)He...
  42. A

    Francis Turbine And Kaplan Turbine Doubt

    While doing experiments on a francis turbine, i noted that the discharge decreases when the load on shaft was increased, =>the speed was decreased. I was(in fact, I am) kind of confused about why it dropped, I did consult some text but didnt get any right reason. I thought that since the blade...
  43. R

    MATLAB MATLAB numerical evaluation doubt

    Hi! I need help from someone that knows something about numerical methods in MATLAB. Specifically, fsolve. So, I have an equation L = K(x) - F(x,y). Given the values of L and y, I need to determine the value of x numerically. So, here's what I've done: G(x) = L- K(x) + F(x,y) in the...
  44. P

    Is every strictly increasing function onto?

    If I want to prove that a non specified function f(x) that maps x -->x' is onto could I show that f(x) is one to one and that f(x')^-1 (the inverse function) is also one to one?? Would that be a valid justification to say that thus f(x) must be onto? More specifically I am looking to prove...
  45. rohanprabhu

    Does intensity determine the occurrence of the photoelectric effect?

    For the photoelectric effec to take place for a certain metal, there is a minimum frequency that the incident radiation must have, also called the threshold frequency. Let us call it f_o. The electron is emmitted only when a minimum amount of energy is provided to it so that it can repulse...
  46. A

    Doubt about Bhabha scattering.

    I have one doubt about Bhabha scattering which is scattering between one electron and one positron, two oppositely charged particles. Why should they scatter each other away rather than attract and eventually annihilate themselves, giving rise to the pair annihilation process? (This process is...
  47. R

    What Is IPS in Geiger Counter Measurements?

    Hallo friends, I have some Geiger counter for detecting Gamma rays...By this meter one can measure in IPS (Intensity per second) or Siever/hour...Now i need to know What is this new unit IPS...Does anyone heard about it...or does it directly corresponds to the disintegrations per second...
  48. S

    Doubt from a beginner

    I am just a student of class 11.I got a small doubt ,dont mistake my doubt, i am just a beginner . My doubt is "What is the variation in Ionization enthalpy , electronegativity ,electron gain enthalpy between the isotopes of a element" waiting for my doubt to get cleared .
  49. R

    How Does the Twin Paradox Challenge Our Understanding of Time Dilation?

    Doubt on FRAME of REF(Its killing me!Help) Hello Guys I am really fascinated by Theory of Relativity and although its not in my educational syllabus(not a phy scholar) , I really study a lot about it. Now coming to the point , I have a doubt on FoR and it may be basic, so I hope you...
  50. N

    Help with Optics Doubt: Sign Conventions in Problems

    .Please provide me with some help in optics. This doubt is in relation to the use of sign conventions in optics. Whenever we prove anything in optics, say for example, when we prove the mirror formula or the lens formula or the lens-maker's formula, we apply the sign conventions in the...
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