###### Why is cell phone radiation so feared, and is it really as dangerous as we think? It uses microwaves, which has less energy than even visible light.

INTRO: Today's cellular and Wi-Fi networks rely on microwaves – a type of electromagnetic radiation utilizing frequencies up to 6 gigahertz (GHz) in order to wireless transmit voice or data.5 G applications will require a new spectrum bands in higher frequency ranges above

###### Why in astronomy is distance measured in light 'years'?

The distances which we measure in the outer space are huge. The distance on the earth are relatively small so we measure all the distance in Km, miles or meters.  To give you a simple idea the distance from earth to moon is roughly: 384,400

###### Why the speed of light changes when it goes from one medium to another medium?

We know, magnetic field=permeability/4π)Idlsin(theta)/r^2=>B changes according to permeabilityElectric field=1/permitivity*4π)*q/r^2E changes according to permitivitySince different medium have different permitivity and permeability v=E/B velocity of light changes in various mediums.

###### What's the property of light that doesn't change when it travels from one medium to another medium?

Hmmm... I might get balled out for this, but.....The 4 ‘properties' of ‘light' (photons), are . . . .Velocity, Amplitude, Frequency and Wavelength . SO....‘Velocity' can/does change, through different ‘mediums', whichdepends on the ‘mediums' refractive index.‘Amplitude' can change, relative to attenuation due to the degreeof transparency of the ‘medium'.During ‘transmission'

###### Does sound reflect like light?

Yes it does, and it's a phenomenon you have experienced many times: we call a reflected sound an echo.As with light, for a surface to reflect sound it needs to be smooth enough in relation to the wavelength of the sound which in practice means the

###### Why does light bend around heavy objects?

GRAVITY!Every thing attracts other things in universe. Even it is mass or energy. Light is made up of subatomic particles called photons. Check my post for reason of your answer.Post by Moksha Kumar on The mysterious universe

###### What does light look like if you could travel almost as fast as light?

The theory of special relativity teaches us that no matter how fast you think you are going, you will always measure the speed of light to be roughly 3 /times 10^8 m/s. In other words, you can never gain speed on a photon. This weirdness is part and parcel of special relativity. The difficulties in conceptualizing

###### If we are looking at light from something 13 billion light years away, how near to us was it when the light set out?

If we are looking at light that is coming from 13 billion light years away, then the source of that light has since moved out to about 46 billion light years away.The light from a source that is currently 13 billion light-years out, will come from a place much closer to us... you have to use

###### Does light have momentum because an individual photon of light has mass?

Yes, per MC Physics theory. A real photon, not a mathematical version, has real static and dynamic mass that gives it momentum and kinetic energy. That puts real photons on the same basis, following the same Universal rules and laws as all other matter in the Universe.More on real

###### If air is moving fast enough, could it bend light?

Not in the way you're thinking. But, if air moves faster it will heat up. When it heats up it will change density. A lower density will have a different refractive index. So it will change how the light passes through it.

###### Which is correct, "When passing through air, green light travels faster than violet light" or "When passing through glass, red light travels slower than violet light"?

Neither.Light travels at the same speed - approx. 3 x (10 to the power of 8) meters per second, irrespective of the frequency. In fact, the Speed of Light ‘C' is the constant of proportion in the relation between Frequency and Wavelength - which are inversely proportional to each other.[math]Wavelength =

###### What would happen if the Sun stopped emitting visible light?

Photosynthesis becomes impossible, because all the remaining eligible wavelengths are caught by the ozone layer (somebody correct me if I'm wrong)That leads to total death, even if the Earth doesn't actually cool down. Though I suspect it will: visible light gives quite a bit of the thermal energy input.I mean, microbial life could survive (and stuff

###### If light did not travel in a straight line, how would it affect our vision?

Light is dual in nature, a wave or/and particle. So this affects the way light travels. To keep my answer short, here are few examples where light rays donot travel straight:Scattering phenomenon: Light rays from the sun are scattered before it enters the eye because of which the ray

###### If a light source is travelling at the speed of light, does it emit light?

The answer to your question is a simple yes it does. An observer will observe the emitted light and would MEASURE its speed as

###### Why isn't there light in space, but there is on Earth?

There is light in space. Putting aside the wavelengths humans cannot see and focusing only on the visible spectrum, remember that we only see things because light bounces off and reaches our eyes. Certain things absorb certain wavelengths of light and reflect the rest, which is why certain things are certain colors.If you're asking why space appears

###### If nothing is impossible, can we move faster than light?

We know that the statement "nothing is impossible" is false.It is impossible to know both the position and momentum of a particle within a certain limit. If you precisely know the momentum of a particle it is impossible to know the position of the particle within

###### Does lightning go as fast as light or sound?

Lightning is rather a sequence and a series of events rather than a single thing. It is light and sound. Each travels through a different medium and at different speeds. The lightning has a cause for creation, and another cause for the path of discharge, and yet another for the humongous discharge.The electric fields are first created

###### How does the earth surface absorb shorter wavelengths of sun's radiant energy and reflect back larger wavelengths as outradiation?

The energy radiated by any object is over all wavelengths/frequencies but peaks at a wavelength that depends on its temperature, Since the Sun is at a high temperature, the radiation peaks in the visible (but it also includes radio, IR, UV, etc. in small amounts). This energy

###### In deep intergalactic space, would an astronaut be able to see his own hand?

It depends what you mean by "deep space". If you were far from Earth but the same distance from the sun that Earth is, the sun would be rather brighter, since the atmosphere scatters some light. The further from the sun, the dimmer.

###### If interference between light waves of different frequencies is possible, one should observe light beats, like the sound beats. How can we experimentally look for this possibility?

Interference of light pf different frequencies is possible,

###### Why is there no bounce light on objects in space when it's filled with with bright stars?

Behold!Planets and their satellites in our solar system are not themselves luminous, but reflect light from the Sun. The Moon and Venus (each pictured below) are the two brightest objects in the sky after the Sun itself, and the light with which they shine is ‘bounced' starlight.

###### What makes it possible to see light?

You have eyes is the obvious answer. Eyes are special organs evolved to turn photons into nerve impluses, which your brain can then interpret as

###### Why do we see lightning as light?

When you walk across the carpet and touch a door know you generate a little spark. A lightning bolt is just a much bigger spark. The spark , or discharge of electrons emit frequencies through out the entire EM (electro magnetic) spectrum. That includes visible light, There

###### What is the light of light?

The light you are talking about is light only to us, this is different for different creatures. Some sense UV rays, some sense infrared rays-based on their habitat and evolution. What you are asking is what is light TO light, well I guess that doesn't make sense because LIGHT IS

###### Is light always moving or does it stop?

An alternative view: Light (or similar radiations) is continuous flow of corpuscles. Corpuscles of light (photons) are the most basic 3D matter-particles. Linear motion at the highest possible speed and spin motion at spin speed proportional to its 3D matter-content are fundamental natures

###### How does light travel as a wave?

The reason is the famous double slit experiment Double-slit experiment - WikipediaIf light is passed trough 2 thin slits, the expectation is to see only two horizontal light lines . But instead what you observe is a whole pattern of dark and light.

###### How does light exist if it has no mass (allowing it to travel at light speed)?

Your question is based on the assumption that everything that exists must have mass.Einstein's famous equation E=mc^2 tells us that energy and mass are equivalent - so your assumption has to be modified to

###### How does the moon reflect the sun's light at night, if the sun is not visible?

How does the moon reflect the sun's light at night, if the sun is not visible?The sun is a very long way away from the earth, 93 million miles. The Earth is only about 8 thousand miles in diameter. So,

###### What makes light move?

A disturbance in the electromagnetic fields of charged bodies causes light to move through space.Light is composed of particles called photons. Each photon is a discrete packet of electromagnetic energy which travels at, the speed of light. The packets carry no mass, but they do have an effective mass that is determined

###### How much gravity is necessary to bend light well?

The Schwarzschild radius (historically referred to as the gravitational radius) is the radius of a sphere such that, if all the mass of an object were to be compressed within that sphere, the escape speed from the surface of the sphere would equal the speed of light.R=2Gm/c^2 (formula)The bodies having a radii smaller than

###### Can the soul travel faster than light?

That depends on what exactly is a soul. It might be we having access to another dimension in space. If in that dimension time becomes constant we might be able to travel faster than light. Also if soul is something else like what we see in movies.. we can assume

###### Why can't sound travel as fast as light?

Simply because of the nature of waves we are comparing with are of two different types. Sound wave is a mechanical wave and it needs a medium to propagate or travel. On the other hand light wave is electromagnetic waves and it does not require any medium to propagate.When a sound wave is produced or generated, the

###### If light has no mass, then why is there a limit to how fast it can travel?

All fundamental particles must travel at c, unless the waves are slowed by virtual or real interactions.Particles with a rest mass are slowed by virtual interactions with the Higgs field. Light is slowed down by interactions with charged particles.It is like if you are driving down the highway. If you are a lawful driver driver you drive

###### What can stop light waves? Can they be stopped?

Yes.Sure we can.Not for a few milliseconds but for a whole minute.Back in 1999, scientists slowed light down to just 17 meters per second, and then two years later the same research group stopped light entirely - but only for a few fractions of

###### How can light wave travel in space, as there is no medium for the waves to propagate?

The answer lies in the wave-particle duality nature of light. It travels as a photon in vacuum space but exhibits both wavelike and particle properties when measured.

###### Why does a ray of light bend when it passes from one transparent medium to the other?

When a light ray passes through mediums ,it's velocity changes. Light while changing medium appears to bend due to this change in velocity . This usually occurs as light searches the shortest possible path to move through the medium. You may learn about refraction and it's laws in few other books. Hope it helps!!

###### Is it possible to see the dual nature of light?

To see the wave behaviour just do any diffraction or interference experiment.To see the particle behaviour, you can use a photomultiplier which is capable of detecting single photons.Also that the energy of photoelectrons depend only on the colour and not the intensity.

###### How can light or electromagnetic waves travel through empty space?

So first of all let us not get too much complex. So, what is an electromagnetic radiation?You would say it's a sort of light wave which is formed by nuclear force of by interaction of atoms in form of photons. So you know that the

###### If our sun suddenly stopped emitting light to us, how much light would we receive from the nearest bright sun?

None.The closest sun to us, apart from our own, is Alpha Centauri. Despite being the closest it is still really far away. 93 million miles away. Thus being just a star among thousands you see at night.But the thing that would, somewhat, give us a little bit of light would be Milky Way.

###### Why does the Sun emit mostly infrared waves and visible light, and Earth emits infrared waves?

The peak thermal radiation from a black body is given by Wien's displacement law, which says that the temperature is inversely proportional to the peak wavelength. Real materials have less than perfect emissivity, which varies for different materials and which is strongly wavelength dependent, but the black body value is a good starting point. Thermal radiation has

###### How fast does light from a light bulb travel?

The speed of light doesn't depend on the source. It only depends on the medium through which it's travelling. 3*10^8 m/s is correct for both vacuum and air so long as you stick to one significant figure.

###### What can stop light waves? Can they be stopped?

Yes.Sure we can.Not for a few milliseconds but for a whole minute.Back in 1999, scientists slowed light down to just 17 meters per second, and then two years later the same research group stopped light entirely - but only for a few fractions of

###### Does the moon have its own light?

Nope. No celestial body has its own light besides a star. Now, before anyone tries jumping in & bringing up volcanoes, auroras, and any other source of

###### Why does light travel so fast?

I see there are forty excellent answers, however, I am tempted to add my own view to the lot.At first I thought you wanted to know "why" light travelled as fast as it did. But when I attempted to answer that, I realized I had misunderstood your question. You want to

###### If a light source is travelling at the speed of light, does it emit light?

The answer to your question is a simple yes it does. An observer will observe the emitted light and would MEASURE its speed as

###### Why does light bend when the medium changes?

Whenever light goes from one medium to another its speed changes.And if light hits the medium with an angle,it bends.Let me explain. Lets go with the car analogy.You are driving a car.And on the either side of the road is