Doubt — 399 discussions

The npn transistor is said to function as an amplifier only in its active state (emitter base is forward biased and collector base is reverse biased). It is considered that majority of the electrons reaching the base layer is dragged into the collector layer. So the emitter current (ec) is...

Hello everyone, A few weeks ago I got a test about physics. One of the questions on the test was about a satelite that would go to an other planet, it was doing system tests in orbit, we had to tell if the satelite had weight. I understand it doesn't, because it is falling and so doesn't apply...

Assume a piston cylinder arrangement. External pressure always equals internal pressure ( reversible conditions ). Now consider these two scenarios: Scenario one: q heat is suddenly added to the arrangement causing a temperature rise and consequently pressure rise, but the volume is yet...

Homework Statement Purely a conceptual/ terminology question, a simple yes or no will suffice :) In circular motion, will a point on its circumference will have a LINEAR acceleration which can be broken into two components- the RADIAL component which is v2/r and the TANGENTIAL component which...

Homework Statement Homework Equations None... Newton's laws The Attempt at a Solution Not the attempt, the entire solution is: String length is constant...hence if on the right side of the pulley, the string goes up by x distance then on the right side also the string goes down by x...

So, recently I started learning about electronic components and then I started learning about semiconductors. The one which I've been having some real trouble to understand its function is the transistor. So I bought an electronics textbook called El ABC de La Electrónica (The ABC of Electronics...

I am confused with the electron configuration of central atoms in complex salts eg. ##[Fe(CN)_6]^{2-}## configuration just Fe atom is Now the complex is low spin so the configuration becomes, Now we have 6CN. where will they donate their electrons? Will the donate electrons in the remaining...

Homework Statement if a disk is rotating on another stationary disk and someone standing on the stationary disk stops it what will the final angular velocity of both the disks be? the catch is that both the disks are not co axial. assume ω angular velocity, M mass of big disk.m mass of small...

Homework Statement A rectangular slab of length l=20cm and thickness d=4cm is placed in left of a converging lens of focal length f=20cm. A screen is placed in the focal plane plane of lens (right side of lens).Refractive index of the material of slab increases linearly from u0 at the bottom by...

I was thinking about the situation given my text about a plano convex lens which was produced with a manufacturing defect. It's plane surface is tilted outwards by a small angle 'z'. In the text its written that when a parallel light beam enters the lens parallel to x-axis , it will still be...

Dear All, Please help me clear some doubts about Theorem 3.3.1 in the 1st attachment. The condition ## |a| = |b| ## has only 8 cases right? ## { x+iy. x - iy, -x + iy, -x - iy, y + ix, y - ix, -y + ix, -y - ix } ## so for the condition ## |a| = |b| ## and ## b \bar c = \bar a c...

If I have an object of mass m tied to the lower surface of a vessel having a liquid and the vessel accelerates upwards... From FBD of object, Buoyant force acts upwards, mg down, pseudo force downwards (frame of reference is vessel) T down. Here's the doubt. Why is F(buoyant force) = Vp(g+a)...

If I have a U-shape wire frame and it contains a straight sliding wire and I dip this in soap, a film forms between the sliding wire and the boundary of U shape frame. Why is the force due to surface tension F = 2Tl where l is length of sliding wire? They say there are 2 layers in contact...

Hey there... As far as I know, electric flux is a scalar quantity which means that negative values are smaller than zero. This concept really confuses me since most of the exercises I dealt with suggest that negative flux somehow is larger than zero flux Example 1 the uniform field is directed...

Why must time slow down when a body moves with respect to a reference frame at rest ? Why should its mass and length increase and decrease respectively when a body travels faster and faster ?

Is there any state of matter for fire or electricity ? If yes, then what is the state of matter ?

I understand that if for an instance one object pushes another with a determinate force, the other object acelerates with that force, and the pushing object acelerates in oposite direction with the oposite force as well. However if I punch a piece of paper I don't feel the same oposite force...

Homework Statement Hi, I have a problem related to some quantum concepts. One teacher of mine has tasked me with solving the next problem: Given a particle on its fundamental state in a potential pit of width a, V=0 between 0 and a and infinite at the rest of the space. Suddenly, the width...

I was going through the capacitor lesson in my textbook. In it its written "...both positive and negative plates will produce electric field in the same direction, hence the electric field adds up...outside the plates, electric field is zero since the field due to negative and positive charges...

I have a doubt since I see the next equation and the corresponding matrix: $$ ds^2 = \Bigg( \frac{1-\frac{r_s}{4\rho}}{1+\frac{r_s}{4\rho}}\Bigg)^2 dt^2 - \Big(1+\frac{r_s}{4\rho}\Big)^4 (d\rho^2 + p^2 d\Omega_2^2) $$$$ g_{\mu\nu} = \left( \begin{array}{ccc} \Bigg(...

Hi all I was trying to solve some numerical problems on venturimeter. I got stuck due to a formula, that I was not able to make sense of. It is a conversion of reading of differential manometer in mercury to corresponding reading in water. I've attached the question, please help me understand it.

Dear All, In the 2nd paragraph of the attachment can you please explain to me why we are trying to make ## r(z) = z ## and what does "As r is not the identity..." mean?? and how did the line ## L = 0.5*b + ρe^{θ/2} ## come about? Danke...

Homework Statement A monochromatic source of light 'S' is placed at the principal focus of a convex lens 'L1'. A parallel beam of light or a plane wave front is incident on the narrow slit represented by AB (its width - 'a') Homework Equations So, what my teacher did was, She showed...

Dear all, can you please help me show why the 2nd scenario below has no solution... Theorem 3.3.1 Suppose that a and b are not both zero. Then the equation ## aZ + b\bar Z + c = 0 ## has a, b and c are complex numbers. Z is the unknown complex number. (1) a unique solution if and only if ##...

Our sun rotates in counter clockwise direction and hence frame dragging will be also in that direction. Suppose if we put a satellite in sun's orbit (almost circular) to revolve in opposite direction to the sun's spin, what would happen to the orbit of the satellite? Would it fall into the sun?

Homework Statement A metal ring of mass m and radius R is placed on a smooth horizontal table and is set rotating about its own axis with a constant angular speed ω. What is the tension in the ring ?Homework EquationsThe Attempt at a Solution Consider a small element ds=rdθ .Tension T acts at...

Homework Statement In the XY plane there are two point charges +q at (0, -b, 0) and –q at (0, b, 0) and a ring of radius a centred in the centre of the plane: Find the electric field in all points of the z axis and study the field’s dominant behaviour at distances z >>a,b. Find the electric...

Hello people, In case if I am typing the question in the wrong forum please redirect me. OK, here it goes... I have this stupid question: Suppose we have a sequence 1, 1, 1, 1, 1, 1... It converges to '1'. Consider 1, 0, 1, 0, 1, 0... it diverges right? What about a sequence 1, 1, 0, 1, 1...

Hi , can anybody make me sense of these equation on which i am striking my head for last 2 months. I am trying to understand piezoelectric effect. And in process of which i came to see so called strain based form of equations related to direct(Equation no.2) and reverse(Equation no. 1)...

Hello, I have a doubtaboutthe use of Gauss theorem in the presence of a coductor. If I have a infinite cylindric long shell with a charge density ƍ of radius b and inside of it a cylindrical conductor of radius a, also of infinite lenght, what will be the electric field in a point located...

Sorry, I wasn't sure of the best way to phrase this. This is a common problem I keep having. Here's the definition of a norm: Let E be a vector space V defined over a field F. A norm on V is a function p: V \rightarrow \mathbb{R} such that: \forall a \in F and \forall u,b \in V: (i) p(av)...

Hi to all. :) First of all I'm not cleary a physician, not even an amateur, only a writer and i hope that a so low level of knowledge don't offend anyone ^^' (my bad level and my broken english :look: ) So: I have a question about the MWI. According with the most serious interpretation: we...

hello i have got a 150A breakerMCCB and the cable connected is 95sqmm and load current is 135A is this correct or any changes is to be made? what will happen if the supply is given from 420v 3phase system

Homework Statement Suppose two stars are orbiting each other in circular orbits with angular speed ##\omega## .M1 is at distance r1 from CM wheras M2 is at distance r2 such that r1+r2=d where d is the distance between them . Now i have a little doubt whether the stars are orbiting around...

Homework Statement find limit ##\lim _{ x\rightarrow \infty }{ \frac { { 10 }^{ x } }{ x! } } ## Homework Equations l'hospital's rule The Attempt at a Solution on substitution we get ##\frac { \infty }{ \infty } ## on using l'hospital's rule,what is the result of differentiation of x...

Homework Statement In spherical coordinates (ρ,θ,ø); I understood the ranges of ρ, and θ. But ø, still eludes my understanding. Why is ø only from 0 to π, why not 0 to 2π??

Homework Statement In Taylor's series, the Lagrange form of remainder is given by R_n = \dfrac{f^{n+1}(t)(x-a)^{n+1}}{(n+1)!} \\ t \in [a,x] whereas my book states that it is given by \dfrac{h^n}{n!} f^n (a+ \theta h) \\ \theta(0,1) I don't see how these two are interrelated. Can...

Hello, From the figure how is it possible to say that this line shows amount of liquid while other is amount of solid. In the figure they showed MP is amount of liquid while OM is amount of solid. How?

a) We know that the smallest charge that can exist is 'e' . But in several instances (such as calculating potential energy of sphere of charge ) we consider 'dq' and then integrate it . How can we justify this ? b) We know that 1/2 or 1/3 of e (charge of electron) doesn't exist . But...

Electric potential energy of a charge q at a point in an electric field due to any charge configuration as the work done by the external force in bringing the charge q from infinity to that point without any acceleration.. In this definition, why charge is moved without any acceleration?

Homework Statement While analyzing superposition of waves from two coherent sources ,the displacement from the two sources are written as y1=A1cos(kx-ωt) and y2=A2cos(kx-ωt+∅) .The resultant displacement at any point is given by y=y1+y2 . I am having doubt that why does argument of sine in...

Homework Statement I understand this BCD sum circuit. The only thing that I'm not understanding is why last full adder carry out also triggers an 6-sum in the other part of the circuit. I mean, if the nibble is not an valid BCD number, we sum six to the number. Not valid BCD numbers are...

Doubt in a scene from the movie "Gravity" In the movie gravity, there is a scene where Dr. Ryan Stone (Sandra Bullock) detaches herself from the broken but moving arm of space shuttle (till 0:45 in the following link): https://www.youtube.com/watch?v= As soon as she does, she spins so...

Homework Statement Consider a non conducting ring of radius r and mass m which has a total charge q distributed uniformly on it.The ring is rotated about its axis with an angular speed ω. a)Find the equivalent electric current in the circuit. b)Find the magnetic moment μ of the ring...

I saw in a question related to Signals and systems that the limits were taken from 5- to 10+ where the signs were in the feet of the numbers..lol..i don't know what you call that. What does this mean?

Hello there! I am currently studying the equilibrium of rigid body and encountering a doubt. Now, in their explanation of reaction forces by a roller or a rocker or a smooth surface, they generalize it as in the preceding examples prevent the translation of a beam for example in ONE direction...

Can someone explain this sentence in MOSFET design.. The Since the drain will be at a positive voltage relative to the source the two pn junctions can be effectively cut off simply connecting the substrate terminal to source terminal.

Hi everyone. I was trying to reproduce the calculation needed to include the QCD correction to the low energy electroweak Lagrangian. In particular I am looking at Peskin section 18.2. In equation 18.35 an extra minus sign appears on the numerator of the second fermion propagator. Can anyone...

What does a first / second / nth order frequency mean physically?

Hello! In my studying of work I've always been told that work done (by what? ) = Force (component along its path) times the distance it moves. Mathematically, W=F.s ... My question here is what is the geometrical presentation of saying Force x Distance ... In other words, when we multiply...