1
vote
0answers
39 views

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 ...
1
vote
0answers
31 views

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 ...
0
votes
2answers
49 views

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 ...
0
votes
0answers
35 views

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 ...
1
vote
1answer
29 views

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 ?
2
votes
2answers
218 views

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 ...
0
votes
0answers
96 views

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 ...
1
vote
2answers
61 views

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 ...
0
votes
0answers
35 views

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 ...
1
vote
0answers
36 views

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?
1
vote
0answers
17 views

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?
0
votes
1answer
63 views

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 ...
0
votes
1answer
67 views

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 ...
1
vote
2answers
81 views

Why can the divergence of vector potential be anything?

Purcell in his book was deriving the vector potential $\bf A$ using $\text{curl}\;(\text{curl}\; \mathbf A)= \mu_0 \mathbf J\; .$ After some algebra, he came to this: $$-\frac{\partial^2 ...
1
vote
1answer
78 views

Why phase velocity of light is slower in a dielectric than vacuum?

Why does light speed suffer a reduction when it passes through a homogeneous dielectric medium? I know my math says so, i.e.- a highly polarizable ($\chi$) medium is associated with high $\epsilon$ ...
3
votes
0answers
41 views

Sources for black hole geodesic orbits

I am looking for good sources that discuss both Kerr and Schwarzschild particle orbits (geodesics). Most sources write down the geodesic equations, constants of motion and the Hamiltonian, but do not ...
1
vote
1answer
50 views

The point of charge neutrality in the Hydrogen Atom

If we treat the Hydrogen Atom like the Bohr model then we have a proton in the center with an electron orbiting at some radius (the Bohr radius). In this picture you can imagine the electric field ...
1
vote
1answer
183 views

Understanding Noether's theorem rigorously

I've known about Noether's theorem for some time and reading some things about it recently I've realised I haven't completely understood it. In that case I've been trying to understand a more rigorous ...
1
vote
1answer
57 views

Energy paradox in fluid mechanics

In a fluid, the specific mechanical energy $$e_{mech}= \frac{P}{\rho} + \frac{v^2}{2} + gz$$. Where $P$ is the static pressure, $\rho$ is the density, $v$ is the velocity, $g$ is the gravitational ...
0
votes
2answers
101 views

Why does the critical angle for refraction exist?

When light moves from a medium with a high refraction index to a medium with a low refractory index (water to vacuum), that there exists a "critical angle" at which no more refraction occurs. What is ...
0
votes
1answer
44 views

Planets falling through wormholes

I am writing a story which will use a wormhole of one sort or another as a plot device to put an aliens' planet in our solar system. I'd like to know: How big a wormhole would have to be for tidal ...
-1
votes
2answers
129 views

Most stationary object in the universe

There is an object in the universe for which the Sun appears to be more stationary as it travels through the universe than a star on some other system. There is probably another object for which both ...
1
vote
1answer
134 views

Is max speed of causality (light) proven experimentally?

Is it possible to have an alternative theory which is consistent with experiments supporting GR, but which doesn't mandate a speed limit on causality? In other words, I understand there is ...
7
votes
0answers
103 views

Real world applications of post-1950s High Energy Physics [closed]

Imagine a world where people knew everything we know today except for high energy physics, where their knowledge ends at our ~1950s level. Is there any real world application, any particular piece of ...
0
votes
1answer
59 views

Is there any way to create a globe with gravitational or similar attractive force - earth simulator?

This may sound like a dumb question. Is there anyway to create a miniature version of earth or its gravitational force. A globe or sphere which have force inside it which can attract the things ...
3
votes
0answers
21 views

How does flow rate affect plume dynamics and film properties in PLD?

So I use a home-built Pulsed Laser Deposition(PLD) system to deposit metal oxide thin films. I use a $ 248\ \mathrm{nm KrF}$ laser. I recently deposited two films under slightly different conditions. ...
0
votes
0answers
27 views

Are only measurements registered as events?

When we measure an electron or some other system behaving quantum mechanically, we observe something. Now, this can be called as an event in relativity terms meaning if we live in 1-D spacetime, only ...
2
votes
0answers
77 views

how to analyze the collision of two photons with four-momentum vector? [closed]

Q: If two photons with energies $E_1$ and $E_2$ collide, with their trajectories making an angle $\theta$. Is the following right about individual initial 4-momentums and total initial 4-momentum? and ...
1
vote
2answers
25 views

Using Thermoelectric generator to power another Peltier cooler

i have a feeling that this isnt possible but wanted to double check. Could you use a Peltier plate on a heat source to generate electricity and then use that electricity to power a Peltier plate as ...
1
vote
1answer
62 views

Is there a way to write the Lorentz force in terms of one field, $L$, and one charge, $X$?

I have heard that physicists like to write electromagnetism as one force (the Lorentz force) and define it as $\vec{F_L}\left(q, \vec{v}, \vec{E}, \vec{B}\right) = q\left(\vec{E} + \vec{v} \times ...
2
votes
0answers
24 views

Why are only some materials ferromagnetic? [duplicate]

I've been told in my solid state class, that ferromagnetism occurs when electron spins are alligned. This happens, as I understand it, when it is "energitically favorable" and when the wavefunction is ...
0
votes
1answer
87 views

treat Physical pendulum as point particle

Suppose you have a physical pendulum. When is it possible to approximate the physical pendulum system as a point particle?
1
vote
0answers
49 views

Maxwell Relations - Isentropic Compressibility to Isothermal Compressibility [closed]

I am trying to derive an expression for the isentropic compressibility in terms of thermal expansion coefficient $\alpha_P$, the isothermal compressibility $\kappa _T$ and the constant pressure heat ...
0
votes
0answers
45 views

Chemical Thermodynamics - Maxwell Relations

I am trying to derive an expression for the isentropic compressibility in terms of thermal expansion coefficient $\alpha_P$, the isothermal compressibility $\kappa_T$ and the constant pressure heat ...
0
votes
2answers
49 views

What can be the probable escape speed from the event horizon of a black hole?

Is there any approximate escape speed value from the event horizon of a black hole or is it infinite ?
0
votes
0answers
54 views

Beta decay - Relative probability of electronic conversion for different disexcitations energies

I'm studying, experimentally, beta decay phenomena. Internal conversion of electrons happens when we have a sobreposition between a excited nucleus with it's electronic cloud. The colision between the ...
1
vote
3answers
140 views

Can a particle have no instantaneous velocity at all points of the path taken but a finite average velocity?

I have a question on kinematics. Say the path traced by a particle is given by a Koch curve or Koch snowflake. Now consider the particle starts from some arbitrary point $A$ on the curve and ...
1
vote
2answers
112 views

Does the International Space Station always travels in the same path?

From the 3d visualization http://www.satflare.com/track.asp?q=25544#TOP (the right image with the red line indication the path of the ISS) it looks like always the ISS takes the same path. Is it the ...
-2
votes
2answers
169 views

What stands behind the quantum nonlocality appearing in entanglements, and why Bell's inequalities are violated?

I noticed the question whether Bell's inequalities are based on a false premise, (Could Bell's Theorem be based on a false premise?) but I bring another argumentation of the question. Also I ...
1
vote
0answers
26 views

Escape speed or Escape Velocity? [duplicate]

Which one should be the correct term escape speed or escape velocity? In one book it is given Speed whereas in another its velocity.
0
votes
0answers
141 views

Perturbation Theory Question

How can you work out the average perturbation, from a normal hamiltonian, of all states that rely on the quantum numbers of s = __ and l = __, with the perturbation being proportional to the product ...
1
vote
1answer
85 views

Is there a proof that adiabatic processes only occur in thermally isolated systems?

This question arose when I read somewhere that adiabatic processes can only be done in thermally isolated systems and isothermal processes can only be done in thermally non-isolated system. Now, ...
1
vote
1answer
89 views

Would an object falling on the surface of the Sun look like this? [closed]

I've been playing around with some rustic animation and then I came to simulating gravity over squishy objects, I simulated a squishy ball of unknown "squishiness" (I'm sorry I don't know a lot of ...
1
vote
2answers
143 views

Why polymeric solids are said to be intermediate between crystalline solids and amorphous solids?

Crystalline solids have ordered arrangement and amorphous solids do not. Polymeric solids are simply formed by the joining of some monomeric units. It has nothing to do with ordered or not ordered ...
0
votes
1answer
46 views

Doesn't for a steady-state current, current-density $\bf{J}$ needs to be same everywhere?

For a steady-state current, the relation must hold $\text{div} \mathbf{J}= 0 .$ This implies $$\frac{\partial}{\partial t} \; \rho_\text{charge-density inside the volume}= 0. $$ This further implies ...
1
vote
0answers
48 views

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} ...
-2
votes
1answer
68 views

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 ...
-2
votes
1answer
121 views

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 ...
0
votes
4answers
122 views

Why does the frequency of a Transformer not change?

I was reading about the transformer, when I came across a note by the author that stated that the Frequency is not changed as the flux linked to the secondary coil in a transformer changes. Is there ...
0
votes
0answers
18 views

ECG depolarization potential

On page 12 of 'ECG Interpretation: From Pathophysiology to Clinical Application' there is a diagram showing the potential difference between the terminals of different leads of an ECG machine when a ...

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