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5 answers
If photon energies are continuous and atomic energy levels are discrete, how can atoms absorb photons?
If photon energies are continuous and atomic energy levels are discrete, how can atoms absorb photons? The probability of a photon having just the right amount of energy for an atomic transition is $0$.
Pricklebush Tickletush
- 3,668
60
votes
16 answers
Intuitively, why does putting capacitors in series decrease the equivalent capacitance?
Can someone please explain, intuitively (without any formula, I understand the formulas), why the equivalent capacitance of capacitors in series is less than the any individual capacitor's capacitance?
Let's take a simple case. Say we have 2…
60
votes
4 answers
Why is the shape of a hanging chain not a "V"?
From Wikipedia:
To answer this question: "What is the shape of a chain suspended at both ends?" we can use the variational principle that the shape must minimize the gravitational potential energy.
The gravitational potential energy is highest at…
Jossie Calderon
- 631
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votes
10 answers
Quantum made easy: so what *is* quantum mechanics all about?
Being a physics grad student, I got used to the weird concepts behind quantum mechanics (used to doesn't mean I fully understand it though). What I mean is that I'm not surprised anymore by the fact that a quantum system might be in a superposition…
Jasmeru
- 1,138
60
votes
6 answers
Why is it so inefficient to generate electricity by absorbing heat?
When I turn on a heater, it's supposed to be roughly 100% efficient. So it converts electricity to heat with great efficiency, but why can't we do the reverse: generate electricity by absorbing heat? I have been searching the internet and from what…
Random Name
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60
votes
5 answers
Why can't the light from a candle light the whole of a dark room?
If you light a candle it starts emitting photons, right? And photons travel at the speed of light. But how come they can't light the whole of a dark room? It means that the photons are not reaching the dark corners of the room, but that is…
ansergeyg
- 681
60
votes
6 answers
If water is not a good conductor, why are we advised to avoid water near electricity (no wet hands near circuits etc.)?
How can water be a medium to conduct current while its ionisation is so negligible that, in principle, no current should flow?
Muhammad Hashim
- 737
60
votes
6 answers
Phase shift of 180 degrees of transversal wave on reflection from denser medium
Can anyone please provide an intuitive explanation of why phase shift of 180 degrees occurs in the Electric Field of a EM wave, when reflected from an optically denser medium?
I tried searching for it but everywhere the result is just used.The…
WhizKid
60
votes
10 answers
Why does a body always rotate about its center of mass?
I found after searching that this question has been asked before. But all the answers were not convincing.
Suppose I have a body which is free, not constrained always rotate about its center of mass (COM). Why is that so?
A convincing answer that I…
Shashaank
- 2,767
60
votes
2 answers
Why aren't the lengths of the bars on a toy glockenspiel proportional to the wavelengths?
As you might already know, frequency of musical notes is arranged in a such a way that if, for example, an A note has frequency of $x$, another A note which is placed one octave higher would produce frequency of $2x$.
So here's my childhood toy…
Moctava Farzán
- 1,904
60
votes
6 answers
Why would a spinning space station create a centrifugal force on an astronaut rather than simply spinning around him/her?
We often see films with spinning space station that create artificial gravity by having the astronauts pulled outwards by centrifugal force.
I'd like to know if this would really happen, and if so, why is the following scenario not true:
Take an…
tarmes
- 623
60
votes
7 answers
How did my candle wax crawl up the sides of the jar?
I have an Ikea candle which has sat on my bookshelf in the sun for >5 years. Aside from an hour or two shortly after I bought the candle, I have not burned the candle regularly (in fact, the wick is broken off at the moment).
After sitting in the…
hifkanotiks
- 675
60
votes
4 answers
Does the universe have a center?
If the big bang was the birth of everything, and the big bang was an event in the sense that it had a location and a time (time 0), wouldn't that mean that our universe has a center?
Where was the big bang? What is there now? Are we moving away from…
nopcorn
- 1,269
60
votes
5 answers
Can radioactivity be slowed through time dilation?
Can radioactivity be slowed using the effect of time dilation?
If you put cesium, tritium or uranium in a cyclotron at relativisitic speeds, do their half lives become longer in our frame?
Could this be used as a means to store radioactive material?
Michael
- 974
60
votes
4 answers
Does a photon exert a gravitational pull?
I know a photon has zero rest mass, but it does have plenty of energy. Since energy and mass are equivalent does this mean that a photon (or more practically, a light beam) exerts a gravitational pull on other objects? If so, does it depend on the…
John
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