# All Questions

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### Luminous Efficacy problem for LED. Semiconductor Physics [closed]

You have a white light LED with 100 lumens/W luminous efficacy when biased at 100 mA  and 0.8V.  Assume the diode has ideal characteristics and that luminous flux is linear with  diode current (a ...
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### Doubt in a question about a body rolling up a ramp [closed]

I encountered a question in this year's paper of an exam, and I am in confusion. The question says: A body with mass $m$ and radius $R$ and rolling without slipping with speed $V$, moves up a ...
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### Is Buoyant force a reaction?

When we fall on water. The surface molecules are pushed down and as a consequence molecules below the surface molecules and molecules beneath them and so on are also pushed down. Some of them are ...
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### Sinusoidal variation of a generalised coordinate with its conjugate momentum

The hamiltonian of a system with 2 degrees of freedom is given by: H= 0.5(p12q14+p22q12-2aq1) where 'a' is a constant. I am to show that q1 varies sinusoidally with p1. My attempt was to write down ...
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### Working of electric-tester [closed]

How does the circuit gets completed when we put an electric-tester glow when we put it in the +ve terminal, when actually the electrons flow from the -ve terminal ?
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### On a molecular level, how does heat transfer take place?

When an ice molecule hits a water molecule, the water molecule adds kinetic energy to the ice molecule. Why do the water molecules lose kinetic energy? In other words, why does heat like to go where ...
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### Why doesn't saturation photocurrent depend on frequency of incident ray, keeping intensity constant?

We know that intensity I = nhf, where n is no. of photons striking metal surface per second per unit sq unit area, and f is frequency of incident ray. In the book it was said that if we change the ...
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### Light and Gravity

The gravitational force does not affect the speed of light rather affects the frequency of light (hence light changes colors, red to blue and vice-versa). I know this has been verified but I have ...
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### Bose-Einstein condensate in external field at finite temperature

Suppose at some finite temperature macroscopically large number of interacting bosons condense to form Bose-Einstein condensate (BEC) with some macroscopic wave function. There also exist excitations ...
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### Value of $\langle x | p \rangle$ [duplicate]

In a context of quantum mechanics, why does: $$\langle x | p \rangle = \left(\frac{1}{2\pi\hbar}\right)^{3/2} e^{ipx/\hbar}$$ Is there any proof for this?
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### Motion in Spaces [duplicate]

How does a shuttle move in the space as, the whole mechanism of a rocket is based on 3rd law of newton but, we can not apply 3rd law of newton in space because there is no reactive force in space?
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### Can blue light encounter slower clock time over red?

I am aware that matter with mass experiences dilation and photon is massless. there is no inertial frame where photon is at rest. However, wave form of light has momentum and energy. Blue light wave ...
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### Head on collision of two black holes

LHC was built to collide two atomic particles to study contents within them. There are millions and billions of black holes present throughout galaxies. As collision between the galaxies is common in ...
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### Existence of a solution for geodesic differential equations for a singular metric

In order to determine the geodesics, one must solve the following set of differential equations \begin{align} \frac{d^2 x^j}{ds^2} + {j\brace h\,\,k}\frac{dx^h}{ds}\frac{dx^k}{ds} = 0, \end{align} ...
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### How the infinite electric field of an electron goes through a slit? [closed]

An electron is an indivisible particle and its electric field has to be a constant too. Going through a slit how the electric field goes through the wall and how it will be regenerated behind the ...
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### Explain this contradiction of violation of “ energy conservation ” using classical mechanics

Consider a rocket moves upward with some acceleration for a very small time say '$dt$' then the kinetic energy increases (for acceleration). as well as as the potential energy increases (due to height ...