Doubt Definition and 591 Threads

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. B

    Doubt regarding the Ethernet cable

    Today I am seeing quiet a number of home appliances or entertainment devices (Eg. NEST Module) plugged-in to the Ethernet cable. Since I don't have much knowledge on this topic I have a little doubt. Just consider the example of NEST. In case, I have a NEST device installed in every room of...
  2. D

    A doubt about inductors and capacitors

    [/itex]Hi I am new here :smile: I know (correct me if wrong please :smile:) that inductors store current in its magnetic field, and capacitors store voltage in its electric field But, why when disconnecting a inductor charged from a DC circuit, a spark is produced at the disconnected...
  3. H

    Doubt with proof of integral of odd function

    1. The proof 2. The doubt What I don't understand is when he switch the variable back to x. He says that: \displaystyle \int_{-a}^{0}{f(x)dx=-\int_{0}^{a}{f(x)dx}} But if we have: \displaystyle \int_{0}^{a}{f(-t)dt=-\int_{0}^{a}{f(t)dt}} Then if we switch back to x we should have...
  4. H

    Theoretical doubt with rolling without slipping

    Hi. I'm taking a look at this problem: And my doubt is with step 2 when he calculates the torque. He just says it is Fd. But...why? F only has a component which effectivly does torque. Thanks
  5. A

    Total Internal Reflection a doubt?

    I was reading about a case of total internal reflection in mirrors and something got me curious... Is there anything such as 'weak refractions'?? In the diagram of the mirror I saw, as a ray of light from an object entered a mirror, it was reflected by the silver coating, and then by the...
  6. E

    What Causes Stellar Expansion During Hydrogen Fusion?

    To a close time, i settled my interpretation of expansion of the SUn... When the H=fuel in the core is over, the helium atoms is now having more density. Hence, the pressure increases on the outer H-fuel which ultimately will fuse faster and faster making a great deal of energy casuing...
  7. A

    Doubt in Wheeler's delayed choice experiment

    Sir, I've gone through wheeler's delayed choice experiment recently...i've got few couple of doubts in it..Please clarify them...Actually Wheeler wanted an answer for his questionthat "what happens when a single photon, presumably already determined to get detected as part of a two-slit...
  8. A

    Basic doubt in thermodynamics 2nd law

    I ve read that according to 2nd law,in a closed system where there's no inflow and outflow of energy,the potential energy of such system continuously decreases... So where does/ what is this energy converted to.?
  9. I

    Solve Math Doubt: Why Did This Happen?

    can you explain why this happen? i can't understand thks in advance
  10. A

    Basic doubt in SR regarding speed of light in different frames.

    suppose we have a moving frame and a rest frame..we know time dilution and length contraction had occurred in moving frame wrt rest frame,this is to make sure that speed of light is same in any frame..but this is not the case..consider measurement of speed of light in moving frame wrt rest frame...
  11. G

    Doubt about magnetic permeabilty

    i made core out of Mu metal strips (μ=0.01) to make a transformer, but surprisingly instead of giving higher emf due to its higher permeability it gave poorer results than a laminated iron core...what might be the reason..please help.
  12. S

    Exploring the Meaning Behind the Phrase "Have a Doubt"

    "have a doubt" I notice many posts in the mathematics sections use phrases like "I have a doubt about" instead of "I have a question about" or "I don't understand...". Is "have a doubt about" a phrase that has become popular with young people in the US/UK? Is it a phrase that non-English...
  13. zoobyshoe

    Medical Is HDL-C Really Protective Against Heart Disease?

    "Good" Cholesterol in Doubt http://www.nytimes.com/2012/05/17/health/research/hdl-good-cholesterol-found-not-to-cut-heart-risk.html?_r=1
  14. J

    Probability doubt - where am i wrong?

    There is a dice where probability of obtaining a number is proportional to the number itself. I have done these problems and the probabilties are 1/21, 2/21,/3/21,/4/21,/5/21 and 6/21 In a normal dice when you have to find probabilities of say, 2 and 4 we do it by favourable cases / total...
  15. H

    Semiconductors + p-n junction doubt

    When electrons from N region diffuse to P region, the electrons combine with holes to form a -ve negative ion leaving behind a +ve ion in P region.So, my doubt is how the holes accept the electrons and get a negative charge because as the holes are positively charged, when they accept the...
  16. H

    Understanding Equivalence Relations: Simplifying Vectors with Linear Algebra

    Hi. I've starting working with vectors in linear algebra but I need to have previous knowledge of equivalence relations so I started studying that but I have a simple doubt with the following relation: $$R = \{ (a,b)/a,b \in A,{\text{ a - b is an integer multiple of 2}}\} $$ In this case could...
  17. J

    Is the Common Base Theorem Applicable to All Cases Involving Triangles?

    Consider the case of a rectangle ABCD, with diagonals AC and BD drawn. Now, it's easy to see that triangles ADC and BCD are congruent. So, the ratio of their areas would be 1. But when I try to obtain the same result via the common base theorem, the line passing through A and B never meets...
  18. A

    A doubt regarding the proof of kirchoff's law of thermal radiation

    In the proof that I have studied, there is a Isothermal cavity that behaves as a black body. there is another small opaque body inside the cavity at the same temperature with emissivity e, absorptivity a and area s. now the irradiation on the small body is Eb = σ times T raised to 4. now the...
  19. H

    Doubt with a theorem that if f is cont. at interval it has max

    I THINK this theorem in short words states that if a function is continuous in an interval [a,b] then it has a maximum. But I have a doubt with the demonstration when it supposes an absurd: $$\begin{align} & \text{THEOREM:} \\ & \text{ }f:[a,b]\to \mathbb{R}\text{ continuous} \\ &...
  20. H

    Understanding $\mathbb{K}$ and $\mathbb{R}^n$ - Get Your Answers Here

    Hi. What does that mean when we see: $$\mathbb{K}$$ what set is that? definitely not the reals, integers, etc. and $$\mathbb{R}^n$$ Is that the reals or what? Thanks!
  21. A

    Doubt about the dimension of a 2nd order homogeneous equation

    My doubt is that is dimension of a 2nd order homogeneous equation of form y''+p(x)y'+q(x)=0 always 2 ? or dimension is 2 only when p(x),q(x) are contionuos on a given interval I..??
  22. S

    Understanding the Differences between Fourier Series and Fourier Transforms

    Hi Do Fourier Transforms give us actual amplitude/phase of the particular frequency (ejωt) just like Fourier series? Thanks Salil
  23. D

    What Provides the Centripetal Force for Circular Motion?

    If a body is rotating in a circular orbit then what is the moment of net force acting on it about the axis of rotation?
  24. A

    One doubt about string theory.

    I read somewhere that one power of string theory is that there is no adjustable dimensionless parameter in the theory. Why is this considered a strong point in favour of string theory? Second, how does the theory help in solving cosmological constant problem? Again there is no adjustable...
  25. C

    The doubt of Seperation of Variables

    The method of separation of variables is used to solve the problem of partial diffrential equation. For example, when the partial differential equation is: \frac{\partial u}{\partial t}-\alpha\frac{\partial^{2}u}{\partial x^{2}}=0 We could suppose that u(x,t) is a solution concerning...
  26. K

    Why I doubt the generality of Gauss' law: A Gaussian sphere 1 light year across

    Let's say I have a Gaussian sphere 1 light year across with synchronized clocks and sensors all over its surface. All clocks are co-moving, not accelerating, and the spatial curvature is negligible. If I have only one charge inside the Gaussian sphere, 1 centimeter from its surface for an entire...
  27. R

    Is It Possible to Extend Flame Duration Beyond 100% Duty Cycle?

    Hello, I am making some modifications in my programm that had written by someone. it is about a flame machine and AC mains frequency is 50Hz. Now, the program is working for outputting a 20ms continuous flame that means it is quiet clear that it was working at 100% duty cyle(not...
  28. Z

    Doubt as to application of Wien's displacement law

    Do Wien's displacement law hold true even for bodies with emissivity not equal to 1, that is, non-black bodies?
  29. R

    PID Control Doubt: Tuning Proportional, Integral & Derivative Gains

    Hello, I have been obsessed with PID control concept and i want to notice you my doubt here. PID controllers are very useful in industrial applications to make the error free process(learned from the web). Basic PID controller mechanism is to tune the values P(Proportional gain)...
  30. dexterdev

    A doubt regarding saturation mode of BJT

    Hi all, I have a doubt regarding saturation mode of BJT. Saturation occurs when both emitter-base junction and base-collector junction gets forward biased. For forward biasing a silicon p-n junction only 0.7V is needed. So is for emitter-base junction. But not for base-collector junction...
  31. R

    Vierd doubt about object collisions

    I just got a doubt regarding object collisions and could not find any relevant information on web. I suppose to put on my question here for help. when the two objects that are independent or dependent together are colliding each other, an other third object want to pass through these objects...
  32. Telemachus

    Silly doubt: ideal gas eq. of state entropic representation

    Hi there. I have a silly doubt about the entropy of mixing for ideal gases The entropy of mixing is this (Eq. [1]): S_{mix}=\sum_j N_j s_{j0}+\left (\sum_j N_j c_j \right) R \ln{\frac{T}{T_0}}+\sum_j N_j R \ln {\frac{V}{N_jv_0}} Now I don't know what identity the book uses to rewrite this on...
  33. Telemachus

    Silly doubt about thermodynamics: molar representation

    Well, I have a doubt about something that I've found in the book. It's really silly, but it's been bothering me for a while, so perhaps you can help me to understand this. As you should know, the fundamental equation of a system can be represented in the entropic representation as a function...
  34. T

    Circular Motion Edexcel A level Doubt

    Circular Motion Edexcel A level Doubt ! Homework Statement In Formula One racing, cars often take corners at speeds in excess of 50 m s-1, and so there is a very real danger of skidding. (a)At a corner of radius 260m the track is banked at 20°. Calculate the maximum speed if no frictional...
  35. J

    What Happens if Coefficients of Kronecker Delta are Zero?

    Well I don't understand this equality: A^{j}_{i}*A_{j}^{k}=\delta_{i}^{k} It is true because it is the result of a calculation. But assuming it is true ¿What happens if one of the A_{i}^{j} is zero?. Then it does not matter which is the value of the A_{j}^{k} the equality will be false...
  36. P

    Doubt about quicksort algorithm

    Good evening, I have a doubt concerning the worst case scenario of the quicksort algorithm, based on the number of comparisons made by the algorithm. Every source about this subject seems to agree that the worst case scenario is when the list to be sorted is already sorted and the pivot is...
  37. P

    Is f(x) = ax + b Truly a Linear Function?

    Hello, I was going through the same problem. From what I can see on the net, one of the relations a linear function has to express is: f(u + v) = f(u) + f(v) Now if f(x) = ax + b is linear then f(u + v) = a(u+v) + 2b So f(u + v) is not equal to f(u ) + f(v). So why is f(x) = ax...
  38. V

    Thermal condution? little confusing can u to remove my doubt.

    thermal condution? little confusing can u please help to remove my doubt. According to law of thermal conduction dQ/dt=-kAdθ/x. variable have their usual meaning. first of all i want to know what is meaning of dQ/dt in this law?? If we see it in a cylindrical object with it's curved part...
  39. N

    Does Electronegativity Vary in Different Bonded Atoms?

    i wanted to ask this…. 1. if an atom forms a bond with some atom of different element,say C-O ,then since O attracts elec more ,can we say tht it now it has less electronegativity compared to only O? 2. in a tertiary carbon why do electrons get pushed towards the central C,is it because of...
  40. L

    Why you can't prove a single mathematical thing beyond a shadow of a doubt

    Oyez! I'm an amateur philosopher and I'd like to start up an interesting debate. The topic will be mathematics (and, in general, everything) and how it is not logically possible to prove such a system. This is my informal argument: 1. Humans live in a "reality" governed by laws, axioms...
  41. J

    Finding (p-1)(q-1) with Good Precision - Number Theory Doubt

    Given a number pq that is the product of two positive integers p and q, is there any way of finding with good precision, (p-1)(q-1)? Or any approximation at the least? Thanks in advance! :D
  42. J

    How to react when students doubt the validity of scientific theories

    I encourage my students to participate in class and think for themselves. I often get questions or remarks about concepts that I teach that stem either from a misunderstanding of an idea, or lack of clarity as to the evidence in support of a theory. I usually find these to be helpful in...
  43. H

    Understanding Markov Processes and the Impact of Varying Variables

    Hi all, This is not a homework question, but I think it's reasonable to post it here. Say, for a Markov process, Pr(Z_{i+1}|Z_{i},...,Z_0) = Pr(Z_{i+1}|Z_{i},Z_{i-1}), people prove that if we consider V_{i} = (Z_{i+1},Z_{i},Z_{i-1}), it would be a 1st-order Markov process, i.e...
  44. L

    Electric potential - doubt in sign convention

    Electric potential --- doubt in sign convention Homework Statement Revered members, I know dV = -E.dx so E = -dV/dx So E should be E = -V/x . But while deriving capacitance of a parallel plate capacitor when dielectric medium is introduced we use E = V/x. But how E = V/x? Homework...
  45. K

    A doubt regarding work and energy

    I was just confused now. Is there work being done if I lift a bucket of water straight up? I know there is something about "work being done BY the bucket" and "work being done ON the bucket". Since I'm not moving horizontally does it mean that no work is done on the bucket? But I'm still...
  46. M

    How to Find Δh for Gravitational Potential Energy Using Trigonometry?

    In this question 3 bi http://www.xtremepapers.com/CIE/International%20A%20And%20AS%20Level/9702%20-%20Physics/9702_w07_qp_2.pdf to find gravitaional poteintial enrgy we need to find Δh. which is the vertical difference between the two spheres shown in the diagram. How do i find that? Answer...
  47. H

    Doubt regarding definition of magnetic susceptibility

    Intensity of magnetisation(I) is defined as the magnetic moment per unit volume of the material. It represents the extent to which a specimen is magnetised. I=M/V Magnetising force or magnetising intensity(H) is defined as the number of ampere turns flowing round unit length of toroidal...
  48. A

    Twin Paradox: Accelerating, Turning Back & Decelerating

    hi... In the twin paradox, we consider that one of the twins went out of the surface of Earth ACCELERATING , then suddenly TURNED BACK and then DECELERATED back towards the Earth with some relativistic velocity………. Why is it so? What if the twin goes on a round trip around the Earth and...
  49. G

    Melting Points: Solids in Tube - Will Temp Remain Same?

    I have 2 solids in a tube. If i start heating the recipient, will the temperature remain the same at the melting point temperature of the substance with the highest melting point?
  50. B

    How to Integrate exp(x)*erfc(x) in MATLAB?

    I have doubt in MATLAB How to integrate exp(x)*erfc(x) ? in MATLAB The warning msg it is displaying is : EXPLICIT integral could not be found
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