Questions related to the perception and measurement of light (primarily in the visible range), its mathematical description, the reproduction of colors by different means, color combinations, etc. Please use the tag [electromagnetic-radiation] if you want to refer to the general form of light.

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2answers
928 views

Does diffraction occur before interference?

In the double slit experiment, light passes through two slits and the waves interfere and form an interference pattern. A single slit is required for diffraction. So, I was thinking about whether ...
4
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2answers
100 views

Could you view yourself in high gravity situations?

I'm trying to understand what effects gravity can have on light. First of all, I don't understand how gravity can even affect it, since it doesn't have mass, right? That is probably a separate ...
4
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1answer
49 views

Shadow of a ripple?

Suppose a stone is thrown into a pool of crystal clear water and its a bright sunshiny morning. You can observe a shadow of the wave in the bottom of the pool. Why does this happen? Is it due to ...
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4answers
577 views

Why do the passing objects' shadows run in the direction of the moving train?

While travelling in the train on the sunset, I have noticed the strange phenomenon. The shadows of the lonely trees and lampposts, that stay along the railroad, are moving on the wall in the same ...
4
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1answer
707 views

Why same formula describing Doppler effect in the case of light in different situations?

I made comparison between Doppler effect in light and sound and one interesting thing that I saw was that in the case of sound there are different formulas to find the apparent frequency in different ...
4
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2answers
204 views

Is light's path a wave?

In a lot of textbooks I see a schematic of light drawn as a squiggly line. I have even heard that some things are too small to be seen because they are smaller than the wavelength of light (and ...
4
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1answer
391 views

Photons arriving from the Sun

Given that the Sun is a bit less than 10 light minutes away from Earth, is it correct to assume in principle (I understand actual processes in the core of the Sun make the situation at a photon's ...
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4answers
242 views

Why does it require such little energy to create the fastest thing in the universe?

I have noticed when I turn on the light switch in my house light comes from the bulb. How is this light created?(process occurring in the bulb) and why is this small amount of electricity enough to ...
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2answers
224 views

What are the lines visible between two cards held edge-to-edge?

Hold two cards (say credit cards) edge to edge, anything from a very slight touch to about 1/3 mm separation, in front of any ordinary light source. When I do this I see several fine dark parallel ...
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1answer
220 views

Why is the shadow of earth red?

Reading this article about the forthcoming eclipse on December 10th, I noticed mention that the moon passes through the red shadow of Earth; I'd always held the impression that a shadow is universally ...
4
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1answer
367 views

Lunar twilight and sixth magnitude stars

Summary: when the Moon is x degrees below the horizon, it interferes with stargazing the same as astronomical twilight would. What is x (as a function of the Moon's phase)? We define civil, ...
4
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1answer
59 views

What, if anything, makes primary colours distinct?

I've recently become interested in the primary colours; red, green and blue. In my capacity as a computer programmer I'm well aware of how these colours are used practically, and of how varying ...
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1answer
117 views

What causes these rainbow effects using a polarizing filter on an airplane?

I know that light reflected from a surface at 45° is polarized and that for a similar reason skylight arriving from a direction orthogonal to the sun is polarized too. Photographers make use of this ...
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1answer
104 views

Why “colours” of light are given in wavelength not frequency?

If I understand correctly, when a beam of (monochromatic) light passes through media of different refractive indices, its wavelength changes but frequency remains constant. Why, then, are colours of ...
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2answers
120 views

Is there something equivalent to a diode for light?

In electronics a diode is a component allowing current passing in only one direction, and blocking the other side. I'm wondering if something similar exists for visible light or other EM waves, like ...
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1answer
122 views

If I'm running away from chasing gamma photons, I can see them, right?

Suppose Bruce Banner goes back in time, convinced that the Hulk is a stupid menace. Let's say he also borrows Quicksilver's speed abilities (maybe the Flash is more appropriate, but based on the ...
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1answer
875 views

Does light induce an electric current in a conductor?

I know that electromagnetic waves induce electric currents in conductors and that's the basis for radio, wi-fi etc. I also know that light is also an electromagnetic wave. So, can light induce a ...
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3answers
12k views

Why can't light pass through walls but sound can?

When I sit in a room I can hear voices coming from the adjacent room but the light in adjacent room does not enter my room i.e. sound waves travels through the wall but light waves can't. Why?
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1answer
47 views

Interference and windows

The other day i was learning about interference patterns with the effect of a bubble making a rainbow on the surface. I learned that the reflections from both sides of the soap can interfere ...
4
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1answer
307 views

If atoms have specific energy levels, why do opaque solids absorb all visible light, not just some? [duplicate]

Here's my question: if atoms have well defined energy levels and those differences correspond to the frequencies of light that can be absorbed, how is it that opaque objects absorb all or most visible ...
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2answers
897 views

Difference between Scattering and Fluorescence

It is often said that substances, objects have color because they selectively absorb all color of sunlight except one. The wavelength that is not absorbed reaches our eyes and we perceive it as ...
4
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3answers
908 views

Real image with converging lens?

I read in a AQA GCSE book that: A real image is formed by the converging lens if the object is further away from the principal focus/focal point. I did this experiment in class: Here is my ...
4
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2answers
669 views

Does thin film interference (anti-reflective coating) let more light through?

The theory of an anti-reflective coating is that the reflected light off the coating and the reflected light off the substrate is 180 degrees out of phase, causing destructive interference and ...
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3answers
2k views

Seeing colors: photons vs waves

As an atmospheric physics major I am familiar with electromagnetic radiation in the atmosphere and what dictates what wavelength objects will emit at. When observing radiation in the atmosphere it is ...
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2answers
2k views

Can 2 beams of ultraviolet light intersect and be visible where they intersect?

Is it possible that if you have 2 ultraviolet lasers, that are invisible to the human eye, and if you aim their beams to intersect at some point, that the place of intersection will show a lower ...
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3answers
207 views

Why most of physics is somehow related to light? [closed]

It seems that for the past 200 years, every physicist is concerned about light. For example : Newton's particle model, Young experiment, Photo-Electrict effect and Einstein's formula, Special ...
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3answers
110 views

Why does the light reflecting off of ocean water sometimes appear 'smoother'?

Looking out the window at some water in the Harbour - I noticed that some parts of the water appear 'smoother' than others. My question is: Why does the light reflecting off of ocean water ...
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1answer
73 views

Experimental determination of speed of light

How is the speed of light measured by the most current method i.e. using lasers and atomic clocks? Alternatively, is there a better method?
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1answer
130 views

How do mirrors look & behave atomically?

I was observing mirrors recently and I was thinking about how an mirror would look atomically. I was always used to looking at atoms as being colored that said, I was always concerned at how they ...
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2answers
135 views

What is the physical structure of light?

Conceptually, I understand what light is, but I don't know what a photon would "look like" if it could be frozen in space/time. For instance, the notion of amplitude seems to be absent when discussing ...
4
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1answer
106 views

Sunrise/Sunset on a planet with an A-Class or B-Class Star

I'm a sci-fi writer, and I have a question regarding a hypothetical planet that orbits an A-class or B-class Star. Assuming Rayleigh Scattering occurs roughly the same way on this planet as it does ...
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3answers
138 views

Possibility for contact lenses that enhance the vibrancy of color

Would it be possible to develop oculars that would enhance the vibrancy of color? I know there are many digital filters to improve vibrancy, but are there physical devices able to produce the same ...
4
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1answer
117 views

What is the intensity of this light?

I am struggling with a derivation that calculates the cross sections for Mie scattering and since the incident light is considered to be a x-polarized plane wave I thought that we would have $$I_i = ...
4
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1answer
558 views

Young's double slit experiment viva question

My professor asked me (in my viva exam), "If, in the Fraunhofer single slit diffraction experiment, if we have 2 slits instead of one (at very short distances), What would happen?" I answered with ...
4
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1answer
2k views

Gravitational Redshift around a Schwarzschild Black Hole

Let's say that I'm hovering in a rocket at constant spatial coordinates outside a Schwarzschild black hole. I drop a bulb into the black hole, and it emits some light at a distance of $r_e$ from the ...
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5answers
215 views

What about a surface determines its color?

Light falls on a surface. Some wavelengths get absorbed. The other are reflected. The reflected ones are the colors that we perceive to be of the surface. What is the property that determines, what ...
4
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3answers
167 views

How is it possible for the wavelength of light to change in a medium?

So my physics class has just finished a long unit on optics while at the same time I've been trying to teach myself relativity. I admit my understanding is probably rudimentary, but I figured all the ...
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2answers
147 views

Do black holes cause gravitational redshift? [duplicate]

Suppose a light ray is emitted by a light source very close to the black hole's singularity away from the black hole's gravitational center. Why won't the light escape? Shouldn't the massive gravity ...
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6answers
311 views

Bending of light from a moving light source

First I will have to explain my question. Look at the image below. This shows doppler shift when an object is moving horizontally to the direction of the wave. Keep the word 'horizontally' in mind. ...
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4answers
467 views

What will be the relative speed of a photon in a light ray to another photon of opposite direction light ray?

If two light rays start simultaneously in the space from exactly opposite ends in opposite direction that is separated by a distance of 600000 km in a way they meet at the mid point (300000 km from ...
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0answers
100 views

Optical Bloch Oscillation

I have a doubt about how the optical Bloch oscillations happen in a 1D photonic crystal. I try to explain: in a photonic crystal with discrete translational symmetry in one direction I superimpose a ...
4
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1answer
793 views

Was the choice of red/green colors for traffic lights a happy coincidence?

All of us have learned since secondary school that the reason we use red in the traffic lights for "Stop" is because it travels the furthest without dispersion. According to wikipedia which cites ...
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2answers
181 views

Explain the notion of light/electromagnetic waves/photons to a non-physicist

A non-physicist asked me about special relativity. My explanations naturally were based on gedankenexperiments involving light. This forced the question: "What is light? It is particles, isn't? Or is ...
4
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3answers
234 views

Light wave crossing media and the relationship between speed, wavelength, and frequency

There are many threads on this topic (like this one) but one aspect about the equation $ v = \lambda\nu $ still confuses me. I have read that frequency does not change when light crosses into ...
3
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4answers
41k views

Why do diamonds shine?

I have always wondered why diamonds shine. Can anyone tell me why?
3
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5answers
4k views

Eye sensitivity & Danger signal [duplicate]

Why are danger signal in red, when the eye is most sensitive to yellow-green? You can check luminosity function for more details...
3
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5answers
272 views

Isn't all light polarised?

I apologize if my question does not make sense.(I'm teaching myself microscopy.) So reading Fundamentals of Light Microscopy and electronic imaging by Douglas&Murphy, at one point the author ...
3
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2answers
15k views

Is black a color or absence of color? [closed]

Is black a color or absence of color? When there is no light, everything is black, so how can we say that black is a color?
3
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4answers
361 views

How are we able to view an object in a room with bulb..?

This is a very basic question on optics. How are we able to view an object kept in a room with a bulb? From what I understand, light rays from bulb will hit the object and some colour will be ...
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4answers
1k views

What is difference between white objects and transparent objects as far as photons are concerned?

Transparent materials let photons through because the energy gap of electron is so large that the photons cannot be absorbed. If the material absorbs a photon, the photon disappears; does this mean ...