Light Question

[davcro]

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Chapter 10, Passage 2, Question 13 on pg 269

Q. What is true of different colors of light in a medium?

A. As frequency increases, the energy decreases
B. As wavelength increases, the energy increases
C. As speed decreases, the wavelength decreases
D. As frequency increases, the wavelength decreases

Answer: http://fromoldbooks.org/Montanus-America/00130000-decorative-initial-d-q75-494x500.jpg

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I picked C. Because when light goes from one medium to another, its speed and wavelength decrease, but the frequency remains constant.

Choice D only makes sense if we are in a vacuum.

 

[chiddler]

The question says "in a medium" so I assumed the medium does not change. If medium is not changing, speed is not changing so that eliminates C. A and B have incorrect correlations.

 

[davcro]

im an idiot. I was thinking in terms of refraction. I didn't think there was a way to change the frequency of light, but there is a way to change its velocity.

 

[MedPR]

B almost got me because I always confuse myself with large/long/small/short in wavelength.

A. As frequency increases, the energy decreases -- Frequency up, energy up. wrong.
B. As wavelength increases, the energy increases -- wavelength up, frequency & energy down, wrong.
C. As speed decreases, the wavelength decreases -- this could be true, but as chiddler said I guess you should assume that speed isn't changing since it says "in a medium" and not "in changing media" This is tricky because you immediately think of v=freq*wavelength, and frequency is dependent on the source, so it is constant. So you would think speed down = wavelength down, which is true if the speed was changing.
D. As frequency increases, the wavelength decreases -- freq up, wavelength down. right.

 

[SaintJude]

Speed of light is a constant. It's always c = 3 x 10^8 m/s.

When it comes to light, there is always a choice trying to make you consider how speed could change. But the speed of light is constant.

 

[milski]

Maximum speed of light (same as speed of light in vacuum) is constant. Light does move slower in different media but the speed stays pretty much constant for a single media.

 

[Whiteshoes]

The question says "in a medium" so I assumed the medium does not change. If medium is not changing, speed is not changing so that eliminates C. A and B have incorrect correlations.

So we should assume that speed can not change unless you change mediums correct? and if you do change mediums then the speed does change but the frequency stays the same therefore the wavelength must changes.

 

[MedPR]

So we should assume that speed can not change unless you change mediums correct? and if you do change mediums then the speed does change but the frequency stays the same therefore the wavelength must changes.

Yea, the speed won't change if the medium doesn't change (at least not for the mcat). Frequency doesn't change unless the source changes, so if velocity changes, wavelength must be changing.

 

[SaintJude]

Maximum speed of light (same as speed of light in vacuum) is constant. Light does move slower in different media but the speed stays pretty much constant for a single media.

Ah, thanks milski for the correction.