Doubt — 399 discussions

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...

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...

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...

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.?

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

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...

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.

"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

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...

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...

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...

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...

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...

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} \\ &...

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!

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..??

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

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?

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...

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...

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...

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...

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

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)...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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...

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

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...

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...

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...

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 energy we need to find Δh. which is the vertical difference between the two spheres shown in the diagram. How do i find that? Answer...

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...

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...

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?

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

Hello , I have this question in my mind from long time. There are two travelers in two trains and one observer on ground(Stationary). One train is traveling at 99.99% speed of light and another train is traveling at speed of light . My question is that the person who is at light speed train...

I found on my notes that for an NMOS with increase in Vsb voltage Body Effect increases, Vt also increases. But it is mentioned that with Vgs constant id increases which I feel is wrong since id is proportional to (Vgs - Vt)2. Hence I think id should decrease. Please show me the light :-)...

Hi, I have a microphone sensor and when i am reading that datasheet, they have written it in as SENSITIVITY -12mV/Pa. I am not sure, what does it mean. Can someone clear me?

Canal rays experimental set up -- a doubt in this Homework Statement Please go through my attachment. It has been mentioned that luminous stream of particles were observed behind the cathode. Homework Equations Behind the cathode means , Whether right of the cathode or left of the...

Hi, I hope it is a very simple mistake and easy to spot. Suppose you start at rest so initial velocity is 0 and you accelerate constantly over a certain distance. An acceleration vs. distance graph (not time) would be like a rectangle. The area under the graph would be A=as=(s/t2)*s = v2...