Speed of Light

Assuming the speed of light in air is already known (it is close to the speed of light in a vacuum), you might check how the light refracts when it changes from air to water (at what angle), and then use Snell's Law.

Galileo used two distantly-separated lanterns in his experiment.

Galileo knew that light traveled very quickly, but did not appreciate how fast it really is. Standing on a peak at night with a shuttered lantern, he sent a colleague with another lantern to a peak some miles away, where the lights would still be visible to each other when opened.

At a prearranged time, Galileo would uncover his lantern. The colleague, when he saw the light from Galileo's lantern, would uncover his own lantern, so that Galileo could then see it. The time between Galileo's uncovering and the time he saw the other lantern would be the time it took light for a round trip equal to twice the distance they were apart.

The result, as would be expected today, was that the colleague saw the light practically as soon as Galileo uncovered it, and uncovered his own, which was then visible practically instantaneously to Galileo. No matter how far apart they were, the brief time lag was identical.

Considering the reaction time by the assistant, and the time taken to open the lantern, Galileo reasoned that light traveled far too quickly to be measured.

Light travels fastest in a vacuum. Other than that, it would travel fastest in a very dilute (low-pressure, and therefore low-density) gas.

n= sin i/sin r

n = refractive index

i = angle of incidence

r = angle of refraction

or

refractive index =velocity of light /phase velocity

phase velocity =lambda/time

For the refractive index of a certain substance:

n=velocity of light in a vacuum/velocity of light in the substance

Refraction comes into play only when the light travels from one medium into another medium. The speed of light is different in different media, so the wavelength changes due to refraction. The formula for wavelength is the ratio of the speed of light to its frequency. The most important point is that the frequency character of light remains constant eventhough it travels in different media. Hence the wavelength is directly proportional to the speed of light. So as speed changes, the wavelength also changes accordingly.

Technically, this question is flawed, since one of the most important rules in physics is that no matter that has mass can travel at or above the speed of light (this is why scientists argue that traveling back in time is impossible) you would need extreme force and very special circumstances.

However, for hypothetical purposes, lets say that you are able to reach the speed of light. When you turn on your headlights, nothing out of the ordinary will happen. You will merely see the light speed away from you at the speed of light. It would be the same as if you were standing still in your car and turned on the headlights.

This is one of the must incredible things about the speed of light (c) - it is constant for everybody. Even if you were an onlooker and you somehow saw the car go by, it wouldn't happen at twice the speed of light, it would still happen at regular (c). Going further, since the speed of the light viewed doesn't change, then what does? The time. If you are able to go near the speed of light (like .9999 times), time would go more slowly for you (compared to normal, but you wouldn't notice anything. If you look at the outside world, time would appear to be traveling faster. For example, going .9999 times the speed of light, traveling for one year would actually be 70 years for anyone else. If you were able to reach the speed of light, you will have esentially stopped time, and if you were able to go faster than the speed of light, there would be an inertial frame of reference in which you would be travelling back in time. This is actually a very touchy subject, i highly recommend reading more about it. There are some very interesting videos and books by Stephen Hawking on youtube that you can watch, both about light, relativity, time travel, all of that.

Because the speed of light is the only constant in the universe, its speed is independent of the reference frame of the observer. It's also because time is not a constant. It takes a bit of thought and openmindedness to get this to stick. Let's take a trip. We'll jump around a bit, so buckle up. Atomic clocks keep time by monitoring the radioactive decay of an unstable nuclide (or radioisotope, if you prefer). If we wind up a pair of them and stick them in a room by themselves for a while to get acquainted and sync up, we can begin an experiment. We take one clock (selected by a coin toss) and put in on an airplane, fly it around for a while, then bring it back. We then stick it back in the room with its twin and compare the times. The clock that went on the trip slowed down and now runs behind the clock that stayed home. The clock that went on the trip had time slow down in its inertial frame. That's because time is not a constant. By any way you try to measure time, it moves more slowly in an accelerated frame. It really does. If you guessed that astronauts who have gone into orbit have had their aging processes slowed down a bit, you'd be right. Not much, but we're all just a bit older (relatively speaking) than those space cadets who return compared to them. This almost sounds like the application circular logic to explain why the speed of light is a constant. But the speed of light really is a constant, and since speed is distance per unit time, and time is not constant, that "allows" light's speed to be constant.

Darkness is not an entity, so it does not travel and has no speed. In principle, a shadow or nonentity could "travel" faster than the speed of light. For example, if you pivoted a powerful laser a few degrees the point of light would travel across a screen very far away at a "speed" greater than light. Note that this is not at all faster than light motion. You could achieve a similar effect by casting shadows on things very far away. But none of this is actually a "speed."

v=fλ (velocity (m/s)=frequency (s^-1) * wavelength (m)


When dealing with light v=hf is also useful (same derivation as for above), where h is the Planck constant.

The characteristic wavelength of an electron = h / p, where

h = Planck's constant;

p = the electron linear momentum = electron mass * speed = g * electron rest mass * speed; and

g = the Lorentz factor to account for the electron-mass change with speed.

Known facts:

h = 6.63 × 10-34 [J s]

electron rest mass, me = 9.11×10-31 [kg]

electron speed, v = 1.5x108 [m/s]

c = speed of light in vacuum = 3x108 [m/s]

v/c = 0.5

g = 1/sqrt(1 - v2/c2) = 1/sqrt(0.75) = 1.1547

Therefore, p = 1.1547 * 9.11×10-31 [kg] * 1.5x108 [m/s] = 2.7e-29 [kg m s-1]

Hence, the electron wavelength

= 6.63 × 10-34 [J s] / 2.7e-29 [kg m s-1]

= 2.46e-5 [m] or 2.46x10-5 [m].

Q.E.D.

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Your question isn't really clear. Speed can't be expressed in just units of distance.

It must be a rate, distance per unit time. Such as, miles per hour, or miles per second,

miles per picosecond.

In an attempt to answer your question though, the speed of light is

-- 186,282 miles per second

-- 670,615,000 miles per hour

-- 16,094,764,800 miles per day

-- 5,878,612,800,000 miles per year

-- 0.000 000 186 3 mile per picosecond

It depends on the material. The speed of light in a vacuum is c = 299,792,458 m/s. Any other material will cause the light to slow down and can be calculated from the material's refractive index. So, for instance, quartz has an index of refraction, n = 1.45. The speed of light in a quartz optical fibres will be:

v = c/n = 206,753,419 m/s.

The propagation speed of a fibre is usually given in terms of a percentage:

V = 100 x c/n.

For the quartz fibre, the propagation speed in 69% of c.

Optical fibres use the property of refraction to keep the light 'inside' the fibre. Using an inner core fibre and an outer 'sheath' fibre with a lower refractive index, the light can be totally internally reflected within the fibre with no need for mirrored surfaces.

No, the speed of light is fastest in a vacuum, where it travels at approximately 299,792 kilometers per second. In other mediums, such as liquids, the speed of light is slower due to interactions between the light and the atoms in the medium.

The speed of light when traveling through transparent materials is slower than in a vacuum. This is due to interactions with the atoms within the material. The speed of light is determined by the refractive index of the material, which is a measure of how much the speed is reduced compared to a vacuum.

Nuclear fusion is the joining up of two smaller nuclei into one larger, in our sun it is the fusion of hydrogen which produces helium, and releases energy. Nuclear fission is the splitting of the nucleus of uranium which releases energy, as in a nuclear reactor.

We'll get consequences if the speed of light is not constant. GPS won't work, for just one off the top. GPS has clocks that are "tweaked" to account for the relative velocity of the satellites (which are called "birds") because they're moving around us. A consequence of c not being a constant might be that time is a constant. And GPS wouldn't work because the clocks of the birds are biased to account for their differential velocity. It's not much, but it's real and it's included in the system. And if c was not constant and time was, then the time base on which GPS functions would be "off" and the system would present gross inaccuracies with its readings. Which it doesn't, even with the clocks of the birds keeping different time than what we use here on earth. We always thought of time being a constant, and it took Einstein and his revelations to shake us out of that thinking. We now know that time is not constant, but light speed is. And that means that something else must be not constant. And it is time that is not constant. There is a bit more to this, but what is posted is a sufficient response to answer the question.

The biggest disadvantage is that as we understand physics today, we can't see how it would be possible.

A smaller disadvantage is that for longer journeys the traveller would experience relativistic time dilation, time on board the vehicle would appear to go slower when compared to outside time.

It'd happen for short journeys too, but then the difference would be too small to cause any trouble.

Also, as we understand physics today, there'd be no way of communicating with the vehicle while in transit.

The advantage would be the obvious, travel times would be hugely reduced.

Light changes speed when it passes through a transparent substance, based on the refractive index. For diamond, the dense crystal slows light to less than half of its velocity as measured in a vacuum.

The speed of light in a vacuum is constant everywhere. The speed of light in a particular medium depends on what the medium is. It moves slower in air than in a vacuum, and slower in water than in air.

matter waves as waves travel faster.. however you must know that we assume this condition to balance the Kinetic energy and energy of a photon according to plank's quantum theory and have no experimental proof about it :)