TBR CBT question

[nickelbackfan]

Visible waves of light with a wavelength of 600 nm travel at 3.0 × 108 m/s in a vacuum and 2.0 × 108 m/s in a denser, transparent medium. Based on information provided in the following table, what is the color and wavelength of the light as it passes through the denser medium?

http://www.e-tbrmcat.com/images/tests/test4/physci/exam_4_physci_iq19.gif

Answer is



A


I thought when wavelength changes, the color can change? The explanation says this

"When electromagnetic waves pass from a vacuum or a less dense medium into a denser medium, the speed (v) and wavelength (&#955 of the waves are reduced, but the frequency (ƒ) remains the same. Because of this change in speed and wavelength, the wave front is bent at the media boundary if it does not strike the surface in a perpendicular manner. This is called refraction, which explains changes in the propagation axis. The color we perceive is due the frequency of the light, and not the wavelength. This is why objects appear the same color to us in air as they do in water. Therefore, the color remains orange, eliminating choices C and D. Because the wave speed has decreased, the wavelength must also decrease, so the wavelength cannot be 600 nm."

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[stevenz]

No, colour is an intrinsic property of the wave and is determined by its frequency, not wavelength. The light receptors which perceive colour in our eyes are frequency dependent, not wavelength dependent, since they act on the principle of electron excitation, which is energy dependent. With this in mind, it makes no sense to define colour as being dependent on wavelength (although it is common written in wavelength form for convenience).

 

[nickelbackfan]

ok...so using E=Hf, the color changes based on the frequency since its energy is changing? And in this case, even though the wavelength is changing, the frequency is constant because its from the same source?

 

[stevenz]

No. The energy of light is dependent only on the source of light (in a particular frame of reference). Since E = hf, this means that the frequency of light depends only on the source, which is why its an intrinsic property.

As light enters a medium with refractive index greater than one, light slows down and as a result its wavelength decreases. This has no bearing on the colour, since the energy of light is the same and it will therefore excite the cones in your eyes the same way, leading to you perceiving the same colour. This is why we define colour as frequency dependent. (Incidentally, for our own colour perception, the external medium is irrelevant since all light must past through the vitreous humour before reaching the retina).

 

[nickelbackfan]

ok thanks