Propagating solutions to Maxwell’s equations in classical electromagnetism and real photons in quantum electrodynamics. A superset of thermal-radiation.
14
votes
3answers
550 views
Distorted colors of Google StreetView photographs near electric power lines
This is a followup to my question:
Cyclist's electrical tingling under power lines
Some users presented a convincing picture that the electric shocks under power lines are primarily from the ...
1
vote
1answer
612 views
Does infrared rays pass through polarized glass?
Actually I had asked in another post that "Does infrared rays pass through active shutter glass" but someone just commented that infrared rays dont pass through polarized glass. If infrared rays ...
4
votes
2answers
827 views
Make a semi transparent mirror with copper
The question:
How would you make a semi transparent mirror (50% reflection, 50% transmission) with glass with a layer of copper. For light $\lambda$ = 500nm Try to be as realistic as possible
What ...
3
votes
5answers
362 views
Does Newtonian mechanics predict the bending of the course of light by objects with mass?
$F=Gm_1m_2/d^2$
$F=ma$
$a_g=Gm_{other}/d^2$
In Newtonian mechanics, the acceleration of object A toward object B is not dependent on the mass of object A but on the mass of object B and the ...
0
votes
0answers
59 views
MIT's 230% efficient LEDs. A reprise about cooling
This is a reprise of the question Can someone explain the science behind MIT's 230% efficient LEDs?
The PRL paper doesn't detail what the efficiency of heat-to-light energy conversion is, which in ...
2
votes
2answers
168 views
Understanding Dynamic light scattering
I'd like to understand the physics of dynamic light scattering experiment. In particular I want to understand the basic relation between relaxation time $\tau_q$ and the diffusion coefficient $D$:
...
1
vote
1answer
50 views
Weather Radar Interpretation - Radial Rays
I was browsing the NEXRAD radar feeds (I'm not an expert, just figuring them out) and I came across the following signature (visit the link to view the radar image)
http://cl.ly/3n0y0p0g2M0K2B313g3U
...
2
votes
2answers
400 views
Is all kind of light same speed?
Is there any speed different between blue or red color? Is there speed different? or there are same speed?
0
votes
0answers
190 views
Is Photosynthetic Photon Flux Density (PPFD) a synonym for Photosynthetically Active Radiation (PAR)?
Both have units of $\mu\text{mol m}^{-2}\text{s}^{-1}$ and refer to light in the 400-700 nm range - that activates photosynthesis. However, I just want to confirm that these are synonyms and don't ...
3
votes
1answer
378 views
Rabi oscillation
Let's consider simple two-level system with frequency gap of $\omega_0$ between ground and excited state. Now, when we turn on external electromagnetic field with frequency $\omega < \omega_0$, ...
0
votes
1answer
55 views
The Synchrotron at CalTech
In the Feynman Lectures Vol. 1, it says that the Synchrotron at the California Institute of Technology is capable of producing electromagnetic Radiations with a frequency of $10^{24}$ cycles per ...
3
votes
1answer
273 views
How does the grid on the microwave oven window prevent microwave radiation from coming out?
If I look through the microwave window I can see through, which means visible radiation can get out. We know also that there is a mesh on the microwave window which prevents microwave from coming out.
...
1
vote
1answer
742 views
Light interference maximum and minimum intensity points
This is a very basic question, but I just forgot how to solve this. It's classical physics question.
Suppose that there are two light sources. And some place away exists a screen. How do I find ...
1
vote
2answers
88 views
Gamma Ray Bursts
What is the maximum frequency of the Gamma Rays produced during supernovae? And how are these detected by telescopes without getting some serious damage done?
35
votes
7answers
1k views
Cyclist's electrical tingling under power lines
It's been happening to me for years. I finally decided to ask users who are better with "practical physics" when I was told that my experience – that I am going to describe momentarily – prove that I ...
20
votes
2answers
2k views
Why is the sky not purple?
I realise the question of why this sky is blue is considered reasonably often here, one way or another. You can take that knowledge as given. What I'm wondering is, given that the spectrum of ...
1
vote
1answer
320 views
Relationship between classical electromagnetic wave frequency and quantum wave function + de broglie frequency
As it is.
As I study through classical mechanics and quantum mechanics, I began to wonder whether there is a relationship between classical electromagnetic wave frequency and quantum wave function ...
7
votes
3answers
3k views
Phase shift of 180 degrees on reflection from optically 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 ...
2
votes
1answer
210 views
How is it possible that we see light from shortly after the big bang?
How can astronomers see light from shortly after the big bang? How did we get "here" before the light that emanated from our "creation"?
1
vote
2answers
589 views
Producing photons with same frequency, different amplitude wave
I don't understand how two photons of the same frequency can have different amplitudes, neither how to produce them.
I know that classically the square of the amplitude is proportional to the energy, ...
3
votes
2answers
949 views
The energy of an electromagnetic wave
The intensity of an electromagnetic wave is only related to its amplitude $E^2$ and not its frequency. A photon has the same wavelength as the wave that's carrying it, and its energy is $h f$.
So ...
0
votes
1answer
87 views
$\mu$T in to $\frac{W}{m^2}$ (for interpreting EMF readings)
I am considering purchasing an EMF reader, to collect data about what is being thrown off of power lines and various other sources in the house to reach some conclusions.
An issue is, the meter can ...
-1
votes
2answers
184 views
Why do you get electric field of a light wave?
Why do you get electric field of a light wave in following form: $E(x,t)=A cos(kx-\omega t- \theta)$?( look at: https://public.me.com/ricktrebino -> OpticsI-02-Waves-Fields.ppt, p. 18)
1
vote
1answer
149 views
Do ~1THz oscillators output “light”?
Upon looking at some radiation levels higher than Microwaves, I have come across "Terahertz radiation". According to the article, there are numerous ways to generate such radiation, and that brings ...
1
vote
0answers
244 views
Equations governing mutual inductance and transformers
What are equations for voltage ratio (primary/secondary) of...
the action of a transformer with a turn ratio (turns primary/turns secondary) of X/Y and a toroidal core of cross-sectional radius R ...
1
vote
1answer
46 views
Can extraterrestials detect our messages?
We transmitted several messages to the space and listening to space for signs of intelligent life for years (SETI).
Assuming they have at least the same technology we have, could they detect these ...
9
votes
5answers
508 views
Superposition of electromagnetic waves
The superposition of two waves is given by
$$\sin(\omega_1 t)+\sin(\omega_2 t)=2\cos\left(\frac{\omega_1-\omega_2}{2}t\right)\sin\left(\frac{\omega_1+\omega_2}{2}t\right).$$
For sound waves, this ...
2
votes
2answers
97 views
Luminescence when ripping (answered) and when pouring (not answered)
As a father to a small child, I have often observed this phenomenon but have until i posted this question not found the vocabulary to Google for it.
Can you explain what I am seeing?
In a darkened ...
0
votes
1answer
69 views
What is the new distance for resolution of the images? [closed]
The taillights of an automobile are $1.25\:\rm{m}$ apart. Assume the pupil of a person's eye has a diameter of $5\:\rm{mm}$ and the light has an average wavelength of $604\:\rm{mm}$. At night, on a ...
2
votes
2answers
1k views
How does Newton's 2-prism experiment help to explain why light does not get dispersed into 7-colors in a parallel glass slab?
In a real parallel glass slide(with two prisms imagined to be touching each other to form a parallel glass slide),
The ray of light should pass through the Z in between without any dispersion or ...
1
vote
2answers
475 views
Why did the microwave oven only heat my coffe half as much as expected?
A sticker on my microwave oven states its output effect to be 750W, which is 180 calories per second. This means that heating 250g of water by one degree celsius would take 250/180 = 1.4s.
Now, my ...
5
votes
3answers
1k views
Can anyone explain to me why light is not dispersed into a spectrum through a parallel glass slide, but only through a prism?
The question pretty much sums up what I need to know. Why is it that light only gets dispersed into a spectrum when travelling through two non-parallel sides(like a prism) and not through something ...
1
vote
1answer
183 views
Why doesn't anomalous dispersion allow faster-than-light propagation?
It seems that the phase velocity of light could be greater than $c$, if $\sqrt{\epsilon \mu} < 1/c$, i.e. for anomalous dispersion.
Are there examples of such media? For diamagnetics it seems ...
2
votes
2answers
910 views
How to calculate gamma radiation shielding?
A device emits 0.2 μSv/h of gamma rays. How thick does an aluminum sheet need to be to completely stop radiation from coming out ? What equation is to be used to calculate this ?
3
votes
2answers
1k views
In electromagnetic radiation, how do electrons actually “move”?
I've always pictured EM radiation as a wave, in common drawings of radiation you would see it as a wave beam and that had clouded my understanding recently.
Illustration on the simplest level:
...
6
votes
1answer
331 views
Microwave oven + water: dielectric heating or ion drag?
When you place a water or food in a microwave oven, it heats.
Which process commits more energy to that: dielectric heating, or ion drag i.e. resistive heating?
AFAIK, in distilled water (which is a ...
4
votes
1answer
626 views
Why is light described by a null geodesic?
I'm trying to wrap my head around how geodesics describe trajectories at the moment.
I get that for events to be causally connected, they must be connected by a timelike curve, so free objects must ...
1
vote
2answers
51 views
Does the efficiency of radiation change in any way in the presence of a medium?
I've read that radiation doesn't really require a medium. But if you're taking, for example, the sun's light, then does its efficiency of transmission increase or decrease once it reaches the earth's ...
1
vote
2answers
453 views
Colour emitted at a specific temperature (color temperature?)
There are quite a few nagging questions I have been having over the years, I do not require a full explanation, just some guidance in my assumptions and pointers if I am very wrong.
My basic ...
1
vote
0answers
43 views
References for Radio Optics?
I'm really intrigued by a bunch of questions like 'what do radio waves look like?' 'how much RF radiation is there in the town I live in?' 'why does RF imaging work?'
But I think I need to do some ...
6
votes
3answers
157 views
Where does the light of the Big Bang come from?
I'm wondering whether the residual light of the Big Bang comes from one particular direction and what possibilities do we have to detect its position?
-2
votes
2answers
241 views
About change in velocity of a light wave as it enters a different medium [closed]
$\dfrac {sin\theta1}{sin\theta2}=\dfrac {v1}{v2}=\dfrac {n2}{n1}$
I understand this equation, but what is the velocity of a light wave going through air and what is the velocity/change in velocity as ...
4
votes
2answers
12k views
Why does wavelength change as light enters a different medium?
When light waves enter a medium of higher refractive index than the previous, why is it that:
Its wavelength decreases?
The frequency of it has to stay the same?
1
vote
3answers
379 views
Why does change in speed of a wave make it refract?
When a light wave enters a medium with a higher refractive index (e.g. from air to standard glass) and its speed decreases, why does that make it refract/bend?
I understand that wavelength decreases ...
2
votes
2answers
109 views
How Safe Are Heat Ray Guns?
Could a little meddling with the frequencies of the Heat Ray Gun beam result in frying crowds rather than dispersing them?
1
vote
1answer
149 views
How To Stop A Heat Ray Gun?
What material would be best suited to create a shield to protect from the new heat ray gun?
3
votes
2answers
668 views
Efficiencies of Coupling Light into a Fiber
I am in AMO Physics and work a lot with optics. I just wanted to get an idea of what coupling efficiencies one "should" get in a "reasonable time"* by coupling light into a fiber using different ...
5
votes
5answers
1k views
Why no longitudinal electromagnetic waves?
According to wikipedia and other sources, there are no longitudinal electromagnetic waves in free space. I'm wondering why not.
Consider an oscillating charged particle as a source of EM waves. Say ...
1
vote
2answers
1k views
Microwaves vs Gas or Electric Coil heating of a water boiler in a typical household
Wouldn't it be more energy efficient and or safe to use microwaves to heat our home's water boiler instead of using dangerous gas or hot electric coils that could catch other things on fire? I'm kinda ...
2
votes
2answers
2k views
Penetration versus Frequency
I would like to know the relation between penetrating ability and the frequency of a wave. For example, gamma waves have high frequency and high penetrating power: intuitively I imagined this as ...
