Tag Info

Hot answers tagged

37

You're right that as the temperature increases, shorter wavelengths receive a higher proportion of thermally radiated power, and longer wavelengths a smaller proportion, because of the shifting Boltzmann distribution of your molecules' kinetic energy, and therefore the shifting power spectrum of the light they emit. However, most of the objects you see ...


13

Planck's Law gives us the intensity of black body radiation as a function of temperature: $$B(\lambda,T)=\frac{2hc^2}{\lambda^5}\cdot \frac{1}{e^{\frac{h c}{\lambda k_B T}}-1}$$ If we plot a normalized plot of this curve for different temperatures, you see the following: As you can see, it does look like the higher temperatures make the relative ...


5

For many materials the change in refractive index over the range of visible wavelengths isn't huge, so it's not a bad approximation to take a single value. The range of visible wavelengths is from about 400nm to 700nm, so the middle wavelength is 550nm. As it happens, the sodium D lines are not far from this, at 589nm, and since they are bright and easy to ...


4

The atoms in the lattice can be thought of as coherent re-radiators of the incident photons. This is not unlike the scenario we have in a double slit experiment, where a Huygens construction of the wave front considers each point in the slit as a radiation source. So it might be "opinion" but I think that diffraction is an appropriate word to use.


3

You need to keep well in mind that the sensation of color is a semantic meaning that the human mind's processing attaches to the spectral content of light. The mixing of "primary colors" was experimentally found (first by artists for red, yellow and blue with natural pigments, then later for, usually, red, green and blue by photography and color projection ...


3

Time is a continous flux that goes from the past to the future; you can't stop it, you can only accelerate or decellerate it. From relative theories and from quantum mechanics we know that, in the most of case, the max speed of informations is the speed of light. So we can see events from the past: we can observe the light of a star that, now, is died. Only ...


2

Yes and no. Fusion inside the sun produces light - but the atom are moving so fast that their electrons are not attached - it is a plasma. As such, you would be hard pushed to find emission lines in the sunlight. You will see some absorption lines - the colder hydrogen and helium further out will absorb little bits of the radiation. What you are left with ...


2

I think the answer is very simple if you ask another question, you are implying that both black holes generate the same gravity and that the light passes exactly through the middle between them, so the question is If the light deviates, where will it deviate to? Since given the conditions it's not possible to give an answer to this question, it means ...


2

I don't know how hot campfires get, but let's take 1000K as a nice round number. The Planck distribution for 1000K looks like: (Calculated, as the logo suggests, using this web site.) In my answer to Can a glass window protect from heat radiation? I post this graph showing the transmission of glass in the IR region: And this shows the transmission ...


2

Infrared lasers are much more dangerous to the human eye compared to a visible laser of the same power, because infrared lasers do not trigger a blink reflex, which means the laser has much more time to damage your retina. Your other questions can be answered by reading about the many differing ways that visible and infrared light interact with matter via ...


2

Individual photons are not considered rays. Because of the wave and particle nature of photons, they are much more complicated than what they are generally thought of: a projectile of light. In fact, they do not have an exact measurable position, but do travel in straight line trajectories. What we consider rays are lines perpendicular to the wave front of ...


2

When a wave travels through a rope, the rope goes up and down, the position of all the 'rope-particles' changes, they oscillate and this makes up the wave. With light, it is indeed the electromagnetic field oscillating, but you shouldn't think of the arrows that represent that field in your first picture of light as 'extending into the rest of the space'. ...


2

The accepted airglow answer might be technically true, but it does not answer the question! The existence of an additional and very faint source of green light in the atmosphere does not explain the absence of the green light in the sunset sky gradient. I wasn't satisfied with other answers either. The only satisfactory answer I could find is this one. ...


2

The ray theory of light is equivalent to the Eikonal Equation, which in turn is essentially a slowly varying envelope approximation to Maxwell's equations. If we write the electric and magnetic field vectors as $\mathbf{E}\left(\mathbf{r}\right) = \mathbf{e}\left(\mathbf{r}\right) e^{i\,\varphi\left(\mathbf{r}\right)}$, $\mathbf{H}\left(\mathbf{r}\right) = ...


2

The colour you see in the sky on cloudy nights is due to the reflection of city lights off the clouds. In rural areas, a cloudy night is, as you expected, significantly darker. However, the massive amount of light given off in urban areas reflects back to Earth when there is cloud cover. And so, you see a red-orange hue, similar to the overall colour ...


1

Short answer: use your technique, but use scale factors of 0.690 for L, and 0.348 for M (instead of 0.542 and 0.575), and you will reproduce the luminosity function. Long answer: You're on the right track. I tried to find 'official' scale values for the LMS curves online to combine into the luminosity function, but couldn't quickly get them. You are ...


1

This question is too broad. It involves ALL the objects in the universe which have a surface, i.e., everything. I'm going to avoid giving a lecture here. In some liquids and most gases the electronic structure of each individual atom or molecule is enough to describe their spectra. The "property" you are looking for in the case of solids is the band ...


1

Parallel rays reflecting on a concave mirror do intersect at one point, the focus, if the mirror is a parabola (in 2d plane geometry) or paraboloid (in 3d space geometry).


1

Although glass is an amorphous material, it behaves surprisingly similar to crystalline materials in some respects. In this case, you can imagine glass to be a semiconductor with a large bandgap, at least large enough to be beyond the visible wavelengths. Therefore, all visible light passes through, which makes glass transparent. Obviously, there will be ...


1

Although the shortfalls of focusing more light on the array have been described, a similar question is why you would not mount mirrors to reflect sunlight toward the array only when the incident angle is well off normal. This might provide some of the advantage of tracking the angle of the sun during the day. I think in this case the placement and size of ...


1

1) A stationary charge that has always been stationary is associated with an electric field and only an electric field. The electric field points towards the charge and every point that us equally far away has an equally strong field and the fields gets four times as weak if you go twice as far away. 2) A uniformly moving charge that has always been ...


1

What if I say that the mirror doesn't flip left and right? You've heard it right the mirror doesn't do the flipping. As the above answers say the mirror shows what is right infront of it. It's you(we humans) who think it is flipping. Let me get this in detail Before we begin tell me , 'What makes you think that the mirror flips your left and right?' Or ...


1

I'm going to assume you mean that the light travels on the precise center line between the holes, as iharob did. This sort of symmetry question is very common in physics. Here's a similar question in classical electrodynamics. "If I place a positive charge at the center of a perfect equilateral triangle of equal negative charges, will it move?" Let's say it ...


1

What would happen to light passing through a narrow space between the event horizons of two equal-mass black holes? Would it deviate or follow a straight path? Like iharob and JohnnyMo1 said, the light goes straight. But something else happens to it. See this screenshot of Irwin Shapiro's seminal paper: See where he said the speed of light depends on ...


1

"It is known" that each atom has a characteristic atomic emission spectrum, as long as the atoms are isolated from one another. Emission spectra are usually observed in gases at low pressure. But when the atoms are compressed into solids or liquids, the close proximity of the atoms distorts the environment in which the emission takes place, and shifts the ...


1

White light is a mixture of all wavelengths in visible spectrum. The blue glass has a property to absorb all colors except blue.Hence only blue is transmitted and thus the light seems to be blue.Similarly that yellow light might not be pure ad must be containing some amount of red light,which gets transmitted singlehandedly.I hope this helps!


1

What you learned is correct. More simply, it's a consequence of the "time reversal symmetry" of most of fundamental physics. This symmetry is still present in general relativity. But, it's obscured by the standard system of coordinates. When you transform these coordinates into the Kruskal coordinate system, you not only have a black hole, you also have ...


1

I imagine this effect has to do with the fact that velocity is relative. When you're on the shore, you gauge the velocity of the waves with respect to the shore. When you're in a plane, you're likely gauging the velocity with respect to the other wave crests, which are moving at the same velocity and so there is no apparent movement.



Only top voted, non community-wiki answers of a minimum length are eligible