# All Questions

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### Do Black Holes emit Hawking radiation while engulfing normal mass?

As I read on various sites ,all of them say that Black Holes emit Hawking radiation as one of the instantly created virtual particles near Event Horizon escapes from it.One goes inside it and other ...
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### Linear motion in a constant acceleration

a car start to move from rest and travels along a straight horizontal road with a constant acceleration. Velocity of the car after t seconds is vms-1. Find the displacement of the car during the ...
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### Where I can find quantum entanglement, real experimental raw data

For analysis purpose, I am looking for raw data from real entanglement experiment with spin measured at two detectors, at various combinations of angles, but preferably at a single combination of ...
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### Universe spawned from the death of a hyper black hole?

Some Cosmologists have speculated that the Universe formed from the debris ejected when a four-dimensional star collapsed into a black hole a scenario that would help to explain why the cosmos seems ...
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### Find the Expectation value of harmonic oscillator

What is the expectation value of any two states of harmonic oscillator(let say $|n>$ and $|m>$) given below, $$<n|e^{{\alpha}a^{\dagger}}e^{-\alpha^*{a}}|m>$$ The actual problem is ...
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### Green dot on photos when taking photo facing the sun

When taking a photo towards the sun, I found there is a green dot on the photo. I'm pretty sure this is caused by the sun, the camera has no problem. Question: what is the cause of this green dot? why ...
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### Explanation of a match between shadows and wet floor at Niagara Falls

The question is about the cause of a wet-floor phenomenon. My vacation trip started at Niagara Falls (Canadian side, horseshoe fall on the upper left corner). It was around 10-11 AM, not too sunny yet....
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### Do all smoothly curved pieces of transparent material have a focal point?

I understand that a lens by definition has a focal point but do all pieces of glass with smoothly curved surfaces have a single point at which all parallel rays of light passing through it in a ...
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### Applying Ampere's Law for Two Parallel Wires

This seems a simple question but I'm not able to understand it properly. Say we have two parallel wires carrying same current I in different directions. We need to calculate the magnetic field at any ...
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### Find velocity of ambulance from the observed frequencies?

I have a problem where an ambulance with a siren is traveling past me (a stationary observer) at a constant velocity. When the ambulance is approaching, I measured the frequency at 1000 Hz and as it ...
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### Skeptical of the “Cannon Shot Rule”

What I consider a highly suspect figure was imparted to me today in a lecture and it very immediately did not sit well with me. To wit, this cannon shot rule (see here for a reproduction of the ...
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### Can the Copenhagen interpretation and the many-worlds theory be somehow reconciled?

Is it possible that, at the moment of observation, a timeline is created where an object is in a state which contrasts its state in the current timeline? Using Schrodinger's cat as an example, let's ...
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### Experimental tests of electric and magnetic fields in a gravity field

Has anyone experimentally verified that the measured values of the electric and magnetic fields do not change due to gravity, that there is no post-Newtonian effect on the strength of either $E$ or $B$...
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### Do III-V based photovoltaics “glow” (photo-luminesce) when illuminated but not loaded?

In this nice answer I learned that when the silicon photovoltaics cells on the International Space Station are exposed to the sun, they tend to be cooler when electrically loaded than when no current ...
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### Lightning, Electrical breakdown, and Current

Recently a discussion came up about this gif: http://i.imgur.com/r9Q8M4G.gifv This lead to a few questions about electrical breakdown of insulators. The disagreement we're having is whether or not a ...
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### Can I use an electromagnet as a shark repellent?

I scuba dive, and also spearfish. Doing these sports in the ocean presents obvious challenges since Sharks exist in the ocean. I know about a product called shark shield which uses magnetism to ...
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### Are black holes causing expansion?

If the universe is sufficiently large enough, there should be a black hole in every direction of the sky. So, could there be a game of tug-of-war going on between all of the black holes in the ...
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### Are elements of statistical ensemble fixed or dynamic?

I will use the simplest example I can think of to explain what I am trying to understand. Consider a system with ~10^23 particles in an equilibrium with fixed values of pressure, volume and ...
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### What is wrong with my formulas for a mathematical model of a double pendulum?

I tried mathematics but I've had no response in a month. I wanted to create a computer simulation on Matlab, using a model for a pendulum from this study (A double pendulum model of tennis strokes. ...