Sound vs Color

[mejorization]

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True or False?

Pitch of sound is determined by the frequency, not the wavelength.
Color of light is determined by the wavelength, not the frequency.

I did a FL yesterday that asked if low pressure would change the pitch of sound. The answer was that it wouldn't, even though the speed of sound, and thus, the wavelength is different. But I know that the color of light does change in different media.

 

[NickNaylor]

Sound pitch is determined by frequency. Color is determined by wavelength, and its frequency doesn't change barring any energy changes.

 

[BurghStudent]

Do you mean color is simply classified by wavelength? Given that electromagnetic radiation has a fixed speed (in vacuum) of 3E8 m/s, couldn't color also be classified and determined by frequency?

 

[rockyDoctora]

True or False?
Color of light is determined by the wavelength, not the frequency.

If color is dependent on wavelength, doesn't that also mean that it's dependent on its frequency?

Since the speed of light is constant:

c / freq = wavelength

 

[NickNaylor]

If color is dependent on wavelength, doesn't that also mean that it's dependent on its frequency?

Since the speed of light is constant:

c / freq = wavelength

No. Frequency is ALWAYS constant barring no energy changes. The speed of light isn't constant and varies with the medium which causes the wavelength to shift in various media.

 

[NickNaylor]

Do you mean color is simply classified by wavelength? Given that electromagnetic radiation has a fixed speed (in vacuum) of 3E8 m/s, couldn't color also be classified and determined by frequency?

As long as you assume a constant value for the speed of light, yes. The problem is that this usually isn't applicable.

 

[mejorization]

Do you mean color is simply classified by wavelength? Given that electromagnetic radiation has a fixed speed (in vacuum) of 3E8 m/s, couldn't color also be classified and determined by frequency?

Light only has a speed of 3*10^8 in a vacuum. It is slower in denser media, resulting in a different wavelength of light (but the same frequency). This means that the color will be different in denser media than in a vacuum.

On the other hand, the pitch of sound is not affected by the medium, because sound depends on frequency (which is always the same no matter the medium).

Is that about right Dr. Cox? 🙄

 

[whiteshadodw]

color definitely depends on frequency or energy, both of which should be constant for a given source since E = hf. if it depended on wavelength, then something that was purple outside water would appear another color inside water. purple is purple inside or outside water, but the wavelength of purple isn't the same inside or outside of water. the frequency however, is constant no matter what.

alternatively, think about this way. you can have different wavelengths differing due to medium, but the source still emits at a certain frequency. lets say we took a blue ball (reflects 400 nm light), dispersed it in water, and went underwater to take a look at it. remarkably, its still blue. the speed of light is less in water, the frequency can't change, but the wavelength has decreased to under 400 nm. does this mean we can now see UV light all of a sudden (under 380 nm, or w/e you definition you want)?

the fact of the matter is that when we refer to wavelengths of light, we do it because of convention. not because its what makes the most sense. some physical chemists laugh that the unit used in IR spectroscopy is (cm^-1), its not ideal, its just convention.

 

[Grom]

To the best of my knowledge, whiteshadodw is correct. Consider that when the light reaches your retina, it not traveling in the surrounding medium anyway. It is within the vitreous humor, so when you look at things normally, the wavelength of the light that reaches your eye is actually not the same wavelength as the light traveling through the air towards your eye. Also consider that you detect light because the photons have a specific amount of energy that causes a conformational change of molecules in your eye. The energy of a photon depends on its frequency, not wavelength.

 

[BurghStudent]

Thanks whiteshadow and Grom that makes sense.