# Speed of Light: Exploring Its Variations

• quantizedzeus
In summary: There is a great moment of discovery waiting for you.In summary, the speed of light is constant in a vacuum, but varies in different mediums due to the medium's refractive index. This is because light is constantly absorbed and re-emitted in a medium, causing it to slow down. However, in a vacuum, light is not absorbed or re-emitted, allowing it to maintain its constant speed. This phenomenon is known as refraction and is explained through the formula v = frequency x wavelength.
quantizedzeus
Speed of light...

It makes no sense to me that if the speed of light is always c...then in different mediums why this speed changes...?? I may have got it in a wrong way...But can anyone help me out in detail...(thanks)

The speed of light in a vacuum is always c.

Does it puzzle you that the speed of sound is different in air than in water?

quantizedzeus said:
It makes no sense to me that if the speed of light is always c...then in different mediums why this speed changes...?? I may have got it in a wrong way...But can anyone help me out in detail...(thanks)

Please start by reading the FAQ thread in the General Physics forum.

Zz.

The speed of light is constant in vacuum and it changes in different mediums.
when light enters a denser medium (like from air to glass) the speed and wavelength of the
light wave decrease while the frequency stays the same.
How much light slows down depends on the new medium's refractive index, n.

speed of light (c = 3 x 10^8) is an constant while on vacuum
but c vary in other medium depend on its density. => n = c/v while n = refractive index.
higher refractive index means less density.
CMIIW

quantizedzeus said:
It makes no sense to me that if the speed of light is always c...then in different mediums why this speed changes...?? I may have got it in a wrong way...But can anyone help me out in detail...(thanks)

Seems perfectly natural to me. But don't just say the speed changes. It only gets slower in a medium.

But the fact is that light is constantly absorbed and re-emitted in a medium. The light that goes out isn't the light that came in.

When a light-particle bangs into the electron cloud in an atom in a medium, it dies and is disappeared, and an impostor steals its clothes and runs out the same direction a bit later. Everyone is fooled. Even the cops.

danR said:
Seems perfectly natural to me. But don't just say the speed changes. It only gets slower in a medium.

But the fact is that light is constantly absorbed and re-emitted in a medium. The light that goes out isn't the light that came in.

When a light-particle bangs into the electron cloud in an atom in a medium, it dies and is disappeared, and an impostor steals its clothes and runs out the same direction a bit later. Everyone is fooled. Even the cops.

Speed of light is slower in all mediums except VACUUM.
v=frequency x wavelength

v changes but wavelength doesn't.

as v changes this causes refraction when light enters a different medium.

Keyur said:
Speed of light is slower in all mediums except VACUUM.
v=frequency x wavelength

v changes but wavelength doesn't.

as v changes this causes refraction when light enters a different medium.

I wouldn't include a vacuum as a medium, though. And strictly speaking, does c remain as a constant even with a medium, between re-emissions and re-absorptions?

After reading the FAQ on transmission through a medium, I have to abandon the simple adsorbtion, re-emission model, although the wording at a key point in that article is a bit confusing.

danR said:
Seems perfectly natural to me. But don't just say the speed changes. It only gets slower in a medium.

But the fact is that light is constantly absorbed and re-emitted in a medium. The light that goes out isn't the light that came in.

When a light-particle bangs into the electron cloud in an atom in a medium, it dies and is disappeared, and an impostor steals its clothes and runs out the same direction a bit later. Everyone is fooled. Even the cops.

so the light particle that come in will stay there ?? or what ?

If the light bulb is in the midle of the room and you turn it on the light reaches south wall same time as north wall. Does that mean you multiply the speed of light times 2?

No, it doesn't. Speed is measured from one object to another. Not from one object to two others at the same time. That's not speed.

piroman said:
If the light bulb is in the midle of the room and you turn it on the light reaches south wall same time as north wall. Does that mean you multiply the speed of light times 2?

You need to read up on what light is. Hit up wikipedia and the FAQ here on PF.

## 1. What is the speed of light?

The speed of light is a fundamental physical constant that represents the speed at which light travels in a vacuum. It is denoted by the letter "c" and has a value of approximately 299,792,458 meters per second (m/s).

## 2. How was the speed of light first measured?

The first successful measurement of the speed of light was conducted by Danish astronomer Ole Rømer in the late 17th century. He observed the moons of Jupiter and noticed that their orbital periods varied depending on their distance from Earth, which he attributed to the finite speed of light.

## 3. Can the speed of light vary?

According to Einstein's theory of relativity, the speed of light is a constant in a vacuum and cannot vary. However, there have been some experiments that suggest the speed of light may change in certain situations, such as in the presence of a strong gravitational field.

## 4. How do scientists study the variations in the speed of light?

Scientists use a variety of methods to study the potential variations in the speed of light. This includes measuring the speed of light in different mediums, such as air or water, and using high precision equipment to detect any changes in the speed of light.

## 5. What are the implications of variations in the speed of light?

If the speed of light were to vary, it would have significant implications for our understanding of the universe and the laws of physics. It could also potentially lead to new technologies and innovations. However, more research and evidence is needed before any conclusive statements can be made about variations in the speed of light.

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