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 in electromagnetic induction

    Homework Statement suppose a coil is placed in a changing magnetic field and the circuit is not closed will the current induce in the coil Homework EquationsThe Attempt at a Solution What I thought was that the current flows only in a closed circuit because it needs a potential difference...
  2. ubergewehr273

    Is Ampere's Law Affected by External Currents?

    When we try to find magnetic field due to a set of current carrying wires in a region we draw an imaginary amperian loop and using ampere's law find the magnitude of the magnetic field. ##\oint \vec B \cdot d\vec l = \mu_{0}i_{enclosed}## The RHS involves only the enclosed current inside the...
  3. S

    Understanding Malus Law and Polaroid Intensity: Conceptual Doubts

    Homework Statement It is just a conceptual doubt Homework Equations According to malus law intensity of light through polaroid is I=(Io)cos^2(theta) where theta is the angle between axis of polaroid and incident light. The Attempt at a Solution But when Theta=0 then I=Io but in my book it is...
  4. Iliody

    I Doubt about partition functions in QFT and in stat Mechanics

    Hi, I was studying for my final exam on statistical physics and a doubt raised on my head that was truly strong and disturbing (at least, for me), and that I couldn't answer to myself by now. The doubt is: Given that we have in d dimensions a fermion non interacting gas, the statistical...
  5. Rodrigo Schmidt

    I Doubt about proof on self-adjoint operators.

    So the statement which the proof's about is: For every linear transformation ##A##(between finite dimension spaces), the product ##A^*A## is self-adjoint. So, the proof is: ##(A^*A)^*=A^*A^{**}=A^*A## What i don't understand is why ##(A^*A)^*=A^*A^{**}##. Isn't that true only if ##A## and...
  6. ubergewehr273

    Doubt on conservation of angular momentum

    Homework Statement A uniform thin rod of length ##2l## and mass ##m## lies on a horizontal table. A horizontal impulse ##J## is given to the rod at one end. There is no friction. The total kinetic energy of the rod after impulse will be ? Homework Equations ##Jl=I\omega## ##J=mv_{cm}##...
  7. B

    What is the tension along wire 1 after wire 2 is cut?

    Considering the figure, (a) what is the tension along the wire 1? (b) What is the tension along wire 1 immediately after the wire 2 is cut? Now, if I put myself in a reference frame with y-axis along ##\vec{g}## (with inverse direction) the part (a) is $$\begin{cases} T_1\cdot cos\theta -mg=0...
  8. F

    Please clear my electromagnetism doubt about units

    It is a well known fact that, in electromagnetic units, strength of a shell and strength of current flowing through its boundary are same. See here. \begin{equation} \begin{matrix} \text{i.e.}\: i \text{(biot)} = \phi \text{(biot) } \end{matrix} \tag{1} \end{equation} (a) While converting to...
  9. A

    Idea / doubt about the movement of electrons

    Hi. First, let me introduce myself: I m from Brazil, I studied physics a few years ago and I ended up leaving the course, today I work with software development. I would like to know if you can help me to take a doubt: I came up with an idea that an electron could move so fast that it would...
  10. V

    B Simple doubt in nuclear fission

    Hi all , I have a very simple doubt in the basics of radioactivity . Nuclear fission is the splitting of the nucleus of a heavy atom such as U23592 by bombarding with slow neutrons into two lighter nuclei with a simultaneous release of huge amount of energy . Now my doubt is that - Can a...
  11. B

    Doubt about approximation and limiting case

    Homework Statement A ball is dropped from rest at height ##h##. We can assume that the drag force from the air is in the form ##F_d=-m \alpha v##. I know then the position in function of the height $$y(t)=h-\frac{g}{\alpha} (t-\frac{1}{\alpha} (1 - e^{-\alpha t}))$$ If I take ##\alpha t<<1##...
  12. C

    I Huygens principle from Kirchoff Integral (sign doubt)

    Consider the Kirkoff integral theorem and the Huygens -Fresnel principle/formula (both from Wikipedia): KIT The Kirchoff integral for monochromatic wave is: $$U({\mathbf {r}})={\frac {1}{4\pi }}\int _{S'}\left[U{\frac {\partial }{\partial {\hat {{\mathbf {n}}}}}}\left({\frac...
  13. S

    Work energy theorem and forces at equilibrium -- Conceptual doubt

    A pendulum of mass m and length l is suspended from the ceiling of a trolley which has a constant acceleration a. Find the maximum deflection θ of the pendulum from the vertical. When I used work energy theorem, I got θ = 2 arctan(a/g). But when I took the equilibrium position and equated the...
  14. Telemachus

    Doubt about a discrete Fourier Transform

    Hi. I was checking the library for the discrete Fourier transform, fftw. So, I was using a functition ##f(x)=sin(kx)##, which when transformed must give a delta function in k. When I transform, and then transform back, I effectively recover the function, so I think I am doing something right...
  15. C

    Finding the Ratio of Uncomplexed Zn2+ to Zn(NH3)2+ Using Stability Constant

    < Mentor Note -- New user has been reminded to use the Homework Help Template when posting schoolwork questions > What is the ratio of the uncomplexed Zn+2 ion in a solution that is 10M in NH3, if the stability constant of [Zn(Nh3)4]+2 is 3x10^9. I am not able to understand why they have given...
  16. Pushoam

    Work Energy Theorem: particle, system of particles, rigid body

    Question: A) Derive the work - energy theorem for one particle. B) Check whether it is applicable for a system of particles and a rigid bodyWork - energy theorem for one particle system, total sum of work done by individual forces = work done by total force To show the above equality, let's...
  17. Pushoam

    Angular velocities of drums

    Homework Statement Homework EquationsThe Attempt at a Solution [/B] Since there is no net torque or net force acting on the system( which consists of the system given in the picture), I applied conservation of angular momentum and energy. I took on the L.H.S. the angular momentum or energy...
  18. Rodrigo Schmidt

    Doubt about irrotational flows

    So, i just started an elementar study on hidrodynamics and I'm stuck with something. We have that the circulation in a closed path Γ is given by: ##C_Γ=\oint_Γ \vec v⋅\vec {dl}## And that, in a irrotational flow, ##C_Γ = 0## for any given Γ. But if we have an irrotational vortex wouldn't...
  19. Pushoam

    Uniform polarization and linear dielectrics

    Can a sphere with a frozen - in uniform polarization ## \vec P ## be considered a linear dielectrics? Following the definition of dielectrics given in Griffiths: The electric field inside the sphere, ## \vec E = \frac {-P}{3 \epsilon_0} ## So, ## \vec P ≠ ε_0 χ_e \vec E ## as ## ε_0 χ_e##...
  20. R

    Carnot Cycle: Doubt in Reversible Isothermal Heat Addition

    In Carnot cycle during the process - "Reversible isothermal heat addition" Q (supplied) = ∫pdV This means that the supplied heat is utilized for pdV work. My doubt is if the Q supplied is converted to work in this process then how Carnot cycle can reject heat during the upcoming isothermal...
  21. C

    Doubt with rotating body and force

    Hello. Let's image a bar. In one side is attached to a body so the bar can rotate over this axis. There is no friction between the two bodies. The system is at rest in t=0. A force acts forming a 90° angle with the bar. The bar moves and begin to rotates. The force dissapear. There is no force...
  22. M

    Naive Doubt About Thermodynamic Equilibrium

    This is more of a recurring conceptual doubt that I keep on running into when solving thermodynamics problems. We are taught that variations between extensive state variables in equilibrium are given by the following 'fundamental formula': dE = TdS + \mathbf{J}\cdot{d}\mathbf{x} +...
  23. G

    Doubt regarding voltage balance on capacitors

    The text in the paper says that C1 has Vout/N-1 = Vout/6, C2 has 2*Vout/6 and so on... Can someone please explain how? Source : Liao, Zitao, Yutian Lei, and Robert CN Pilawa-Podgurski. "A GaN-based flying-capacitor multilevel boost converter for high step-up conversion." Energy Conversion...
  24. rbsann

    Electric field calculation doubt (dipole)

    Hello all, i am having a hard time with EM, specially with the most simple concepts that i don't seem to grasp at all and the simple exercises that should be quite simple to solve. So the question is. ( i will omit the constant (1/4pieo) for practice sake When i calculate the eletric field...
  25. cheapstrike

    Doubt related to formation of a differential equation

    Homework Statement Find the order of the differential equation of y=C1sin2x+C2cos2x+C3. Homework Equations - The Attempt at a Solution [/B] I read in my book that the order of the differential equation is equal to the number of arbitrary constants but the answer given is 2. Btw I have...
  26. farolero

    B A doubt about tangential and normal aceleration, pilot g forces

    so a pilot is spining in a circle at a constant speed, the g forces he will feel will be the same than normal acceleration dependant on wr but now you put him inside a tube where he can move along varying the radius of the circle now the normal acceleration will be zero because he is in the...
  27. Thiru07

    Doubt in an inequality problem

    Homework Statement Given : (y+2)(y-3) <= 0Homework EquationsThe Attempt at a Solution Now, I have y-3 <= 0 or y+2 <= 0 Hence, y <= 3 or y <= -2 But how is correct? I think is wrong because y <= -2. Can someone please clarify?
  28. Bloopy

    B Doubt regarding Rutherford's Alpha Scattering Experiment and Impact Parameter

    It is mentioned in my Textbook that if alpha-particle has large impact parameter, it gets scattered through small angles and vice versa. I understand that impact parameter is defined as the perpendicular distance between the path of a projectile and the center of the nucleus. I am unsure how...
  29. V

    A doubt from Kinetic Theory of Gases

    I have read Average translation kinetic energy is 1/2RT per degree of freedom and Average translation kinetic energy for an ideal gases is 3/2RT.How? Does it imply f=3 for all ideal gases?
  30. F

    A doubt about Mechanical Engineering problems and exercises

    Is it true that some mechanical systems( or machines or mechanisms) of problems and exercises of Mechanical Engineering books(engineering dynamics, mechanics of materials, fluid dynamics...) are invented ? That is, they don't exist in real life, they are created only for a particular problem or...
  31. V

    Understanding Heat Transfer in a Closed System with a Moving Piston

    Homework Statement As shown in figure. Homework Equations dq=msdt[/B]The Attempt at a Solution I am unable to understand the question,what is the significance of the moving piston if the ends of the conducting rod is maintained at constant temperature.It is enough if someone could explain...
  32. M

    MHB Order of operations doubt on this expression

    Let's say that we have this expression, $\frac{1}{2}*2x*x-2$ So now solving this in one method we can $\frac{1}{\cancel 2}*\cancel2x*x-2=x^2-2$ In another way $\frac{1}{2}*2x*x-2=\frac{2x^2-2}{2}=x^2-1$ What is the reason that I get two different answers ? I hope that both ways are valid...
  33. NickTesla

    B Indefinite Integral, doubt....

    doubt in this fraction in here Because he, simplify 12 with 4 ?? do not understand! someone could make another example ,with fraction ! Thank you!
  34. A

    What Axis is Used When Calculating Torque?

    When we say torque about a point what axis do we mean,how can rotational motion happen without an axis?
  35. A

    Is the Proof Behind Choosing Any Point on an Axis to Calculate Torque?

    I know that to calculate the torque about an axis, we can choose any point on that axis and find the torque about that point and take the component along the direction of the axis.Buy what is the proof behind this theorem?
  36. M

    Theoretic doubt about the definition of derivatives.

    Homework Statement Hi, this is a question that has been bothering me for a while. (Im in calculus II at the moment) Why do i need to derivate some functions by definition and other times i dont? for example if somebody asks me to calculate the partial derivatives of a branch function in a a...
  37. M

    MHB How do I plot a distance-time graph using TikZ?

    Problem Plot the above given information in a Distance time graph. Where do I need help Hoping my graph is correct Show that the speed in the final 6 seconds is twice the speed in first 6 seconds But I'm having trouble here , I know $ distance=\frac{distance}{time} $ Many Thanks :)
  38. M

    MHB Doubt in factoring a trinomial

    Hey (Wave) (Party), Problem Factor $3x^2+11x+10$ Workings This expression can be separated into, $3x^2+10x+x+10$ Where have i done wrong ? (Thinking) Many Thanks :)
  39. Titan97

    I Is Kirchoff's Theorem Misunderstood in Relation to Power Absorption?

    According to Kirchoff $$e=J(T,f)A$$ ##e## is the power emitted and ##A## is the power absorbed If ##E## is the power supplied, can I say that $$e=E-A$$
  40. C

    MHB Chi-Square Test: Solving Doubt w/ Kepler

    Good afternoon, I'm glad I've joined this forum. Here's my doubt: I have a serie of values in a table like this: Case 1 34 55 Case 2 23 10 Case 3 55 40 etc... the 34 means the observed value, and the 55 the control group, and so on. It's easy to do the test of course if... The problem is: if...
  41. N

    B Why is probability defined in space rather than at a point in quantum mechanics?

    I have started quantum mechanics on my own using online lectures. So i have very basic doubts: 1) probability of electron is defined in space rather than a point. My question is why don't we comment about probability at a point. I thought two possible explanation that: 1.1)ψ2dx the dx term...
  42. Dr. Manoj

    Why Is the Photoelectric Effect Considered Proof of Light's Particle Nature?

    I've a doubt regarding photoelectric effect. It's said that photoelectric effect is proof for light to be a particle. But, when seen into the theory, relations between wavelength and kinetic energy, frequency and photoelectric current are explained. The means we have used wave characters like...
  43. S

    I Manometer reading doubt in the case of viscous fluid

    I wonder if it is correct to read an open air manometer in the case of viscous fluid in the following (usual) way. Consider the situation showed in the picture where a viscous fluid is flowing, in fact ##z_C <z_A##. The reading of the manometer would be ##p_a=\rho g z_a##, ##p_b=\rho g z_b##...
  44. Muthumanimaran

    I Solve Eigenstates Doubt: Prof. Leonard Susskind's Quantum Mechanics

    I am currently reading Prof.Leonard Susskind's Lecture on Quantum Mechanics. In the Chapter: Spin in the arbitrary directions, in the subdivision Eigenstates In case $$\lambda=1$$ Prof states that measuring spin in arbitrary +n state gives me +1 as eigenvalue, what I don't understand is the next...
  45. thegreengineer

    Mechanics of materials torsion doubt

    Good evening. I've got stuck in this question from my book of Mechanics of Materials by Beer and Johnston about torsion. The allowable shearing stress is 15 ksi in the 1.5-in.-diameter steel rod AB and 8 ksi in the 1.8-in.-diameter brass rod BC. Neglecting the effect of stress concentrations...
  46. Vivan Vatsa

    How can I easily understand the relations between different concentration terms?

    I want to ask that how to understand the relation of different concentration terms. Like the relation of Molality, Molarity & Density & related relations of concentration terms. So how to understand the relations easily?
  47. V

    Doubt from second law of thermodynamics

    qrev/T = ΔS here what does ΔS signify?does it mean change in entropy of system or surroundings? how is entropy of system,surrounding and universe related to each other and which entropy is used in gibbs free energy equation?
  48. Ray9927

    Doubt about trigonometry Identities from sin α

    Hi all! I'm Ray and I'm new to this community, it's a pleasure! I'm trying to resolve a trigonometry exercise where I have to calculate the trigonometry Identities of a right triangle but in the specifications they don't show me any common data (hypotenuse or cathethus values), they just leave...
  49. weezy

    I Doubt regarding proof of Clausius Inequality.

    I have attached two images from my textbook one of which is a diagram and the other a paragraph with which I am having problems. The last sentence mentions that due to violation of 2nd law we cannot convert all the heat to work in this thermodynamic cycle. However what is preventing the carnot...
  50. V

    Charged Capacitor: Opposing Emf Battery Series

    can a charged capacitor mathematically be represented as uncharged capacitor connected in series with battery of opposing emf ?
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