Tagged Questions

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.

172 views

Propulsion force on a laser pointer?

How to calculate propulsion force on a laser pointer in reaction to the emitted light power in watts? Should I just divide power by speed of light? Since power is energy per unit of time, hence ...
57 views

Laser beam sensed by scattering

Can a laser beam, whether it is a IR laser or of the visible to human eye spectrum, be seen/sensed by an electronic eye like a photosensor/photodetector, not human eye, if the beam is just in air? For ...
232 views

Carrying light through bleached water: how does it work?

Disclaimer: first time on Physics stack-exchange, I hope I'll be asking the question as per policy of this site, please help me edit if my wording seems off topic. I've seen a project to light up ...
567 views

Sun in front of horizon after sunset; mirage or reflection?

The day before yesterday, I observed sunset while flying over the eastern Mediterranean. After the sun set, it seemed to 'continue' in front of the horizon. I managed to snatch a picture (sorry for ...
88 views

light falling on a completely reflecting friction less mirror

If you had a perfectly reflective mirror whose face was perpendicular to the ground and was kept on a friction less track on the ground, and you shined a flashlight on it, what would happen? Would ...
437 views

Effect of gravity upon light and bagels

According to this question and this web site, photons undergo twice the deflection from gravitational fields as do physical objects. However, the weak equivalence principle states that locally, ...
181 views

Can someone reconcile the Boltzmann transport equation with the Maxwell equations for photons/light?

Having taking courses in both physics and nuclear engineering, I've noticed that the two fields tend to describe photons/light in two different settings. In nuclear engineering, the radiative ...
2k views

Why is the bottom part of a candle flame blue?

What’s the explanation behind the bottom part of a candle flame being blue? I googled hard in vain. I read this. I don’t understand how it’s explained by the emission of excited molecular radicals in ...
987 views

Do Photons Move in a Wave Like Pattern? [duplicate]

In many pieces of literature, light is said to travel like a "wave". Does this mean the light literally propagates through space like a wave as in up and down and so on or does light move linearly ...
135 views

Experiments to the question : why wet is dark?

How can we prove the explanations for: why clothes get dark when they are wet, by experiments?
853 views

How to transform infrared beam into visible range?

I am looking for an easy method of turning an infrared beam into a visible beam. There are some well-known ways to do it, for example a camera objective, but it that is very big and uncomfortable to ...
156 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 ...
1k views

Is there anything that could attract and trap a photon?

Is there any particle or anything that could attract and trap light or photon particle? Can anti photon particle attract photons and trap them ?
240 views

When I turn on white lights, these chairs cast a shadow. However, when blue LED lights are turned on the shadow turns yellow. Why is this? Is this due to interference of light or is it just an ...
299 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 ...
147 views

How does light actually behave?

Senario: I am walking 5 meters/second and have a laser pointer that I shoot a burst of light from perpendicular to to the path I am walking on. Would the light travel perpendicular to the path from ...
94 views

How does gas pressure increase the lifespan of Halogen tungsten lamps in the Halogen Cycle?

I am curious about this passage "Since quartz is very strong, the gas pressure can be higher,[5] which reduces the rate of evaporation of the filament, permitting it to run a higher temperature (and ...
6k views

Will we ever be able to view the past?

By analogy with the sun, whose light is apparently reaching us in 8 minutes, it means that we are only viewing the sun 8 minutes ago when we look up at it. However, what if we were eventually able to ...
397 views

How to arrange mirrors so I can't see myself?

If I wanted to surround myself with mirrors how would I need to arrange them so that if I stood in the middle of them I couldn't see myself in any reflection? For simplicity let's just say we only ...
4k views

Infrared Vs Visible Light

Infrared waves are widely used for quick heating objects, but a quick look at electromagnetic spectrum astonished me and raised a question that how come an infrared wave with lower energy compared to ...
15k views

Why don't fluorescent lights produce shadows?

I have watched light sources such as incandescent lamps and other lamp sources; they have always made shadows. But a fluorescent lamp doesn't make any shadow. What is the reason behind the non-...
775 views

At what rate does light 'bend' around the surface of the earth?

Since the g force of earth is 9.8 m/s*2 does that mean light 'drops' at that rate as it travels past earth? Or is general relativity a lot more complex than that?
456 views

What is the physical significance of the negative amplitude of a light wave?

I want to understand what is the physical significance of negative amplitude of a light wave? In an ac electrical circuit, I understand that negative amplitude signifies the amplitude measured when ...
65 views

How long will a light bulb work isf the glass shell removed?

How long will a light bulb work if it gets its glass shell removed?
1k views

How do we know the wavelength of colours?

Every site and video I have been on doesn't address it directly.specifically I want to know what is are the experiments we derive these wavelengths from and how do we calculate the wavelengths inspite ...
2k views

Can spectacles converge sunlight to an extent that it burns the eyeball?

I need to know whether wearing spectacles can cause optical harm. I saw a movie where one pair of glasses was placed on table exposed to sunlight, then the sunlight converged and focused to a point ...
10k views

How do you measure wavelength/frequency of light

I'm sure this is a trivial question for someone who knows something about electromagnetic radiation, but: how do experimenters measure the wavelength/frequency of light? For example, how do we know ...
291 views

Basic rule for diffraction

I'm a high school student. I still don't understand the reflection, diffraction and refraction of light. It seems to me that in concept of quantum physics, reflection is just a process of object ...
732 views

Rainbow reflected on TV screen? (pic attached)

According to wikipedia, A rainbow is an optical and meteorological phenomenon that is caused by reflection, refraction and dispersion of light in water droplets... Given that we require ...
89 views

Possibility of a Dark Star

I think it was a very early notion, pre-black holes, that there may exist a star that was so massive, all of its outgoing light would return to its source. Is this actually possible? Is there an ...
1k views

How bright is a 150 W incandescent light bulb?

When I was a boy (I live in the UK) most light bulbs were incandescents and they were labelled with their wattage. The brightest bulb you could get was an 150 W incandescent light bulb. Today there ...
261 views

Is light amplitude spatial?

In diagrams I often see light waves depicted as little sine waves that travel through space. And often when describing polarizers, the explainer will angle their hand to show the angle of ...
65 views

Polarization modulation

To increase bandwidth, for EM free space communication, could you modulate the polarization, so that, e.g., for a one-meter wavelength radio wave, the polarization could be modulated between vertical ...
365 views

Why does black glass reflect better than white one?

Why does black glass reflect better than white glass? Both of them are glasses, so they reflect light. But why black glass reflects better? See below, shiny black glass.
66 views

Why are LCDs black? [duplicate]

I had a question on LCDs after noticing something interesting about its color. LCDs are black when they aren't used. But when we observe LCDs closely, we see they are made up of red, green, and blue ...
802 views

what is the whitest material?

I saw before a great question on what is the blackest material. Therefore I started wondering, there are many things that look white but in fact absorb light. So what material is truly white? Or, ...
309 views

How to improve the visibility of light without increasing the brightness?

I am not sure whether or not this is the right SE site to post this question on but I'm sure someone will inform me of my mistake soon enough if it is wrong. Basically I am an Electronic Engineer and ...
434 views

Moving electric charges

I just wanted to double-check these three statements, as I'm not entirely sure I understood them completely: 1) A stationary electric charge (let's say a proton) produces electric field. 2) A moving ...
149 views

I want to know why light even moves at all.

Never mind in a vacuum, why and how does light even move at all? What propels it?
29 views

Does illuminating a conductor with light energy less than its workfunction change the measured conductivity?

For example, does the light absorbed in an exposed metal wire increase the average velocity of the electrons, hence increasing mobility and conductance?
78 views

Intensity of light wave penetrating soft tissue

I'm studying for a medical physics exam and I'm struggling with the following question: Calculate the fraction of energy which penetrates to a depth of 3cm in soft tissue for a beam of light at a ...
38 views

Band of color around a light source [closed]

When a light source, like a phone flash light, is observed in the dark, why is there a band of seven colors observed as a ring around it ?
316 views

Possibility of a free-space hologram

Holograms are real. But they are not what sci-fi calls holograms. From a simple geometric optics standpoint we can see that in order to create the illusion of an object there must be some sort of ...
391 views

Convert normal white light to laser-like light?

Is there a probable device that can convert white light to laser-like light without the need of an electrical stage in-between? I'm thinking of something along this level. A very precise filter and ...
94 views

What are the common points between physical optics and geometric optics? [closed]

I am trying to write a paper about light, I want to discuss the two way of studying light, the physical/wave optics and the geometric/ray optics, but I want to write a general introduction about them, ...
31 views

What does the refractive index depend on? [duplicate]

I've always thought refractive index is dependent on the density of the material. The more denser, the more refraction. But kerosene whose density is higher than water has refractive index less than ...
71 views

What is the maximum light difference for one to be able to see into or out of a building and equally discern objects? [closed]

In this question I am referring to the physics behind not being able to discern objects outside when in a lit room, even though you would be able to discern them if you were outside, even though when ...
214 views

Why EM waves with long wave length traveles long distance cmpared to EM waves of smaller wave length? [closed]

Most of the times i was told with an example that police uses red light because they travel large distance than compared to blue or green or other wave lengths ? ...