Eye disease and contact lenses
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Eye disease and contact lenses
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[ID] => 559900
[post_author] => 12815
[post_date] => 2025-01-09 21:30:41
[post_date_gmt] => 2025-01-10 02:30:41
[post_content] => Practice Passage (Question 1-5)
*This passage is the property of Khan Academy and has been reformatted into an AAMC-style interface in their entirety by MedLife Mastery. MedLife Mastery does not endorse and is not an affiliate of Khan Academy.
Punctate keratitis is an eye disease that results in abrasions on the epithelial cornea. One of the leading causes of the disease is the overuse of contact lenses. The cornea requires exposure to oxygen in order to maintain a healthy exterior. Although it typically gets this oxygen from the air surrounding the eye, contact lenses may prevent this interaction from occurring to its desired potential.
A research team is investigating the optical properties of four new types of clear plastic to be used in prescription “soft” contact lenses. It is hypothesized that increasing the breathability of the lenses will allow oxygen to interact with the cornea through the lenses, circumnavigating one of the major issues associated with contacts. To investigate the refractive capabilities of the different types of plastic the team conducted an experiment by firing a red ray of light toward each type of plastic. The incoming angle θ was measured from the surface of the plastic and the outgoing angle φ was measured with respect to the dotted line shown below.
The data found in the experiment is shown in the following chart.
[post_title] => Eye disease and contact lenses
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[question] => What is the index of refraction of the red light in plastic 1?
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[answer] => 3
[description] => Reason for the Correct Answer:
Try using Snell’s Law
Remember that when using Snell’s Law, all angles must be measured with respect to the normal line)
The incoming angle when measured with respect to normal for plastic 1 is 60°, and the index of refraction of air is 1
n1sinθ1 = n2sinθ2 which after substituting gives 1sin(60)=nsin(43). And solving for n gives n=sin60/sin43
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[answers] => Array
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[0] => Array
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[each_answer] => A.sin-1(60/43)
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[1] => Array
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[each_answer] => B.sin43/sin60
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[2] => Array
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[each_answer] => C.sin60/sin43
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[3] => Array
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[each_answer] => D.sin-1(43/60)
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[1] => Array
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[quiz_unique_key] => 3873426850
[question] => Which of the four plastics has the largest index of refraction?
[value] => Array
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[answer] => 3
[description] => Reason for the Correct Answer:
The material with the largest index of refraction will bend the light the most in this case since it is surrounded by air
Remember to measure all angles from the normal line! That means you must first take 90° – θ
Take the difference between the incoming angles and the outgoing angles when measured from normal to find out which one material bent the light most
For material 3 the incoming angle from normal was 56° and the outgoing angle from normal was 37°. The difference of 56°-37° =19° is the largest angle of deviation, and so material 3 has the largest index of refraction
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[answers] => Array
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[0] => Array
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[each_answer] => A.Plastic 1
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[1] => Array
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[each_answer] => B.Plastic 2
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[2] => Array
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[each_answer] => C.Plastic 3
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[3] => Array
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[each_answer] => D.Plastic 4
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[2] => Array
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[quiz_unique_key] => 83407773
[question] => When the refracted ray of light makes it to the bottom of the plastic, it is possible for it to be totally internally reflected. What is the critical angle for plastic 2 given that the index of refraction of material 2 is n2?
[value] => Array
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[answer] => 2
[description] => Reason for the Correct Answer:
The critical angle occurs when the outgoing angle is 90°
Use Snell’s law, n1sinθ1 = n2sinθ2
Snell’s Law gives n2sinθc = 1sin(90) which gives sinθc = 1/n2
If sinθc = 1/n2 then solving for θc gives θc = sin-1(1/n2)
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[answers] => Array
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[0] => Array
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[each_answer] => A.sin-1(n2/1)
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[1] => Array
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[each_answer] => B.sin-1(1/n2)
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[2] => Array
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[each_answer] => C.sin(1/n2)
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[3] => Array
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[each_answer] => D.sin(n2/1)
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[3] => Array
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[quiz_unique_key] => 2377279144
[question] => A problem that the research team is running into is that the light rays are bending too much when entering the plastics. This is causing the light to miss the detectors they are using to measure the refracted angle. What change to the experiment could the research team make that would decrease the amount that the light bends when hitting the plastics?
[value] => Array
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[answer] => 3
[description] => Reason for the Correct Answer:
Smaller wavelength light bends more than large wavelength light
The smaller the difference of index of refraction between the two media the less the light will bend
Since surrounding the air with a fluid reduces the difference between index of refraction between the two media, it will cause the light ray to bend less
)
[answers] => Array
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[0] => Array
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[each_answer] => A.Use yellow light instead of red light
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[1] => Array
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[each_answer] => B.Use blue light instead of red light
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[2] => Array
(
[each_answer] => C.Submerge the plastic in a fluid of index of refraction larger than air, but less than the plastics
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[3] => Array
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[each_answer] => D.Create a vacuum around the plastic instead of letting it be surrounded by air
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[4] => Array
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[quiz_unique_key] => 2261298308
[question] => If the materials were submerged in a fluid that had an index of refraction larger than the plastics, what would be seen to happen?
[value] => Array
(
[answer] => 2
[description] => Reason for the Correct Answer:
Now the plastic will be a faster material than the incoming material
When light encounters a fast medium it bends away from the normal line, when light encounters a slow medium it bends towards the normal line
Since the light would now bend away from normal line, the light rays would be bending the other direction
)
[answers] => Array
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[0] => Array
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[each_answer] => A.The angles would all get smaller
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[1] => Array
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[each_answer] => B.The light rays would bend in the other direction compared to how they bent when entering from the air
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[2] => Array
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[each_answer] => C.The light ray would not enter the material at all and would completely bounce off of the plastic
)
[3] => Array
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[each_answer] => D.The light rays would no longer bend when entering the plastic
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[559900|1] => C
[559900|2] => C
[559900|3] => B
[559900|4] => C
[559900|5] => B
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