# Tag Info

### The speed of time

Are time and gravity the same thing? No, they are not. Could there be a speed of gravity (cause and effect)? Gravitational waves travel at the same speed as light. In quantum theory both as ...
• 6,831
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### How can light penetrate gold in an astronaut's visor?

Sufficiently thin gold films are not opaque but green: This is near the percolation threshold at which clumps or islands of atoms join to form a continuous opaque film. See also Norrman et al. (1978)....
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### Where/ how does light propagate?

Can you tell how is propagation of light explained now, and if QM altered the current view? The propagation of light is explained by Maxwell’s equations. They describe how the field behaves. In ...
• 64.2k
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### Failure of Newton's corpuscular theory and success of photon theory of light

The corpuscular theory was opposed to the wave theory, and was rejected when diffraction experiments confirmed the wave theory. The blackbody spectrum also confirmed the wave theory at low frequencies,...
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### Failure of Newton's corpuscular theory and success of photon theory of light

As an example, when using the corpuscular theory refraction of light and Snell’s Law is predicted using Newtonian Mechanics but a requirement of the theory is that the speed of light in glass is ...
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1 vote

### Do prescribed glasses transmit light?

Without light transmission, you will not be able to see anything since light is the way of transmitting the picture to your eye.

### What exactly does it mean when a light ray is incident on a surface?

Yes it does mean the angle with the normal.. in this case an incident angle of 30 degrees would mean the incident ray (the light ray flaling on the reflecting surface) makes as angle of 30 degrees ...

### Doubt on photoelectric effect

To say "wave nature of light" means to deal with it as EM wave. The EM energy is $\propto (E^2 + B^2)$. For sinusoidal wave $E = E_0sin(kx-\omega t)$, and $B = B_0sin(kx-\omega t)$, that ...
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### Doubt on photoelectric effect

For the most part the photoelectric effect happens one photon/electron interaction at a time. So the effect relies solely on the energy of each photon and the binding strength or energy required to ...
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### Doubt on photoelectric effect

You are confusing the energy of a single photon with the energy of the light beam. Increasing the intensity of light (while keeping the frequency $f$ constant) does not increase the energy per photon, ...
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### How does the combination of lens create a sharper image?

I'd like to try explain this in the context of information. Images that have the highest resolution contain the most accurate information per unit area. In optics, this image information is carried by ...
1 vote

### How does the combination of lens create a sharper image?

The distance between nerve endings in the retina of the eye places a limit on the sharpness of an image that you can observe. A good lens system can bring the image closer and larger. This can cause ...
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### How does the combination of lens create a sharper image?

It's hard to answer without knowing the context of the statement. But generally, multiple lenses can reduce aberrations. Real lenses aren't perfect, and images suffer because of that. Rays ...
• 21.3k
Accepted

### What happens to the time period when refraction occurs?

The frequency is the inverse of the period. So since the frequency is the same the period is also the same
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### Mutual gravitational acceleration (or deflection) of light beams as a function of the angle between them

Newton's formula $F=\frac{GMm}{r^2}$ is only an approximation, valid in non-relativistic contexts. Light is highly (!) relativistic, and so it's not surprising that the formula doesn't hold for it. To ...
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### Is it possible to visualise red shift?

If a picture of a star or galaxy hurtling away from Earth is taken, does it appear red despite it being a different colour? Would a blue coloured star moving away from us appear red to us or vice ...
• 37k

### Is it possible to visualise red shift?

In order to get a visible (to the human eye) color change because of the Dopler redshift, an object has to: be moving at speeds at least ~5000km/s in regard to the human observer have a distinct ...
• 5,638
1 vote

### How many oscillating fields exist in a light wave?

No one can measure directly that light from a thermal source or from a laser has wave properties. Only the intensity distribution behind an edge allows such conclusions. Everyone should also be able ...
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### Is it possible to visualise red shift?

The standard view of General Relativity is that the locations of galaxies are actually fixed: They don't change, except under the extremely long-term attraction of gravity (the weakest force, acting ...
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1 vote

### Is it possible to visualise red shift?

To detect the redshift of distant objects, we can use the fact that (to the best of our knowledge) the laws of physics are the same everywhere. This means the spectral lines of elements (both ...
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### Why is light not a longitudinal wave?

The confusion here is about a direction of a wave versus its polarization. Even sound waves can be longitudinal and transversal, depending on whether the particles in a wave oscillate along the ...
• 37k
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### How many oscillating fields exist in a light wave?

Disclaimer: It looks like we're talking in terms of classical electromagnetism, so that's what I'm going to do here. If you go all quantum mechanical or relativistic, the answers will be consistent, ...
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### Alternate sky colors?

Aside from scattering, an important contribution to sky color in a purely gaseous atmosphere is absorption. Already on the Earth we have stratospheric ozone which makes twilights blue (see Why is ...
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### Alternate sky colors?

Rayleigh scattering results in scattering inversely proportional to the fourth power of the wavelength. So, no matter what the composition of the scatterer is, the blue will be scattered more than the ...
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### Does light intensity affect transparency

I would like to expand a little on your reflections in the first paragraph. This is important for your second paragraph. ...
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### Convert $\rm Lux$ to $\rm W/m^2$

Unfortunately, you can't get what you want just from Lux ratings. Lux, and candela, and lumens, measure how strongly the human retina responds to the light source. If your sources were extremely ...
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### Light as a wavelength

We obviously have three phenomena that you should take into account in your consideration of light as a wave. The first concerns the generation of light. The second concerns the intensity distribution ...
• 8,479
Accepted

### Strange behaviour of ultra dark image in a CMOS camera?

This was happening due to non-standard ISO values as is clear from the results of my experiments below. The strange values vanish on increasing the ISO. A very peculiar implementation of low ISO ...
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### Light as a wavelength

The first thing I'd recommend is to get in the mindset of how waves move. Find a still pool of water, and toss a small rock into the middle of it. Observe the waves moving outwards in all directions....
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### Light as a wavelength

Let's take the case of an old-school light bulb containing a hot filament as an example. When hot enough to emit light (as in a car headlight) it produces a broad mix of wavelengths that is not ...
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### Light as a wavelength

What direction the light travels from the source, and what range of wavelengths the light contains are separate questions. The sun emits light in all directions, and (in principle) in all wavelengths ...
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### How does the flicker fusion threshold prove time perception?

I am also interested in this subject. Not only is the flicker fusion an indication of the relative speed of processes in differing species, but also the metabolic rate, life expectancy, heart beat ...
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### Two touching surfaces transmitting light: Name of effect

It sound like you are describing an evanescent wave.
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### Relation between impact parameter and distance of closest approach of a light ray in Schwarzschild Geodesics

The quantity $b$ in these equations is the impact parameter and is defined as $L/E$ (in units where $c=1$). It is called this because $L/E$ is the perpendicular distance between the trajectory of a ...
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### EMR and how it works?

Light is a part of electromagnetic radiation, which also includes, for example, infrared (colloquially called heat radiation) and X-rays. As you correctly pointed out, electron emits light, or more ...
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### Destructive interference of light and destroying energy?

I'm certainly no expert on the topic, but I believe that this forms a standing wave in the laser light paths where they cross over. So it seems the energy is stored in the space between the wall and ...

### Aren't all objects luminous in a sense?

As you say, all matter is radiating, even black holes! In principle, the phrase "nonluminous objects" should be qualified by what part of the spectrum they can be considered nonluminous and ...
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### Can Transverse electric and Transverse magnetic waves propagate in free space in general?

In free space you can have waves that are TE and TM, but the TE and TM components decay rapidly with distance to the source (as a power of $R/\lambda$). The TEM components of free space waves decay ...
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### Can Transverse electric and Transverse magnetic waves propagate in free space in general?

A waveguide terminating to free space is an aperture antenna. As with any antenna, the radiated waves in the far field (many wavelengths and aperture dimensions away from the aperture) propagate as ...
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### How do car sunshades work?

My guess is that the black shade is absorbing the heat rather than the air in the cabin. Also, if that shade is an adhesive type of sunshade that actually sticks to the glass then perhaps the heat is ...
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### Aren't all objects luminous in a sense?

Yes, all objects emit radiation. But without other considerations, I would interpret "nonluminous" to simply mean that it isn't emitting visible light. My cat is quite warm, but I would use ...
• 33.6k
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### Aren't all objects luminous in a sense?

Black bodies are in equilibrium with their surroundings - they absorb radiation from their surroundings and then re-emit it. Luminous bodies have internal energy sources, i.e., there is energy ...
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Yes, that's correct in principle. For visible light, the changes have to occur on time-scales of a femtosecond, $10^{-15}$ seconds, and on spatial scales of about a 100 nanometers, $10^{-7}$ meters, ...