A mirror in an operating room
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- A mirror in an operating room
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A mirror in an operating room
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[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.
Operating rooms use bright overhead lights to increase visibility during surgical procedures. The operating room light shown below uses a high power light bulb surrounded by a curved parabolic concave mirror. The light bulb is placed at the focal point of the curved parabolic mirror. The dashed line represents the principal axis of the curved mirror. The point C represents the center of curvature of the curved mirror. The back of the mirror is also metallic, shiny, and reflective.
Figure 1. A diagram of an operating room, including the presence of a light bulb and a mirror.
During one surgery, the following scenarios occur:
Scenario 1: While waiting for her procedure to start, a patient whose face is located near point D is looking up at the mirror along the principal axis. The operating light is not turned on, but the room is bright enough for her to see a reflection of her face in the mirror.
Scenario 2: the patient starts to sit up, causing her face to move along the principal axis from point D to point C.
Scenario 3: Before the operation, the surgeon is looking at his reflection in the back of the curved mirror. The surgeon’s face is located near point A.
Scenario 4: The light bulb was moved from its initial location and placed very, very far away from the mirror along the principal axis, so that the light rays are essentially parallel when they reach the curved mirror.
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[question] => Why is it important to place the light bulb at the focal point?
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[answer] => 1
[description] => Reason for the Correct Answer:
The operating room light should not burn the patient
Light parallel to the principal axis gets reflected through the focal point, and light rays passing through the focal point get reflected parallel to the principal axis
The light bulb should be at the focal point so that light rays emanating from it will be reflected parallel to the principal axis similar to a car headlight
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[answers] => Array
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[each_answer] => A. So that the reflected light from the mirror will be composed of light rays traveling parallel to the principal axis
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[1] => Array
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[each_answer] => B. So that the reflected light from the mirror gets focused into a single point on the principal axis
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[each_answer] => C. So that the curved parabolic mirror reflects all the light and doesn’t absorb any
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[each_answer] => D. So that the curved parabolic mirror does not allow any light to reach point A
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[1] => Array
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[quiz_unique_key] => 3873426850
[question] => What kind of image does the patient see in Scenario 1?
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[answer] => 4
[description] => Reason for the Correct Answer:
The patient’s face is located beyond the focal point of the parabolic mirror
The light from the patient’s face will converge at a specific point upon reflecting off the mirror
Since the light rays will converge at a specific point, the image is real, and all real images are inverted so her face would be upside down
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[answers] => Array
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[0] => Array
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[each_answer] => A. A virtual image that is upside down
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[each_answer] => B. A real image that is right side up
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[each_answer] => C. A virtual image that is right side up
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[each_answer] => D. A real image that is upside down
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[quiz_unique_key] => 83407773
[question] => During Scenario 2, what would the patient see happen to the image of her face?
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[answer] => 3
[description] => Reason for the Correct Answer:
Draw some ray tracings for objects getting closer to the mirror
The face never moves past the focal point
As you approach the focal point, from outside the focal point, the image gets consistently larger
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[each_answer] => A. The image would get smaller then bigger
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[each_answer] => B. The image would get bigger then smaller
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[each_answer] => C. The image would consistently get bigger
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[each_answer] => D. The image would consistently get smaller
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[quiz_unique_key] => 2261298308
[question] => What kind of image will the surgeon see of his face in Scenario 3?
[value] => Array
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[answer] => 3
[description] => Reason for the Correct Answer:
The back of the mirror acts as a convex mirror
Convex mirrors always create images that are virtual
Virtual images are not inverted so the surgeon would see a virtual right side up image
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[answers] => Array
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[0] => Array
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[each_answer] => A. A real image that is upside down
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[1] => Array
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[each_answer] => B. A virtual image that is upside down
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[each_answer] => C. A virtual image that is right side up
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[each_answer] => D. A real image that is right side up
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[question] => In Scenario 4, what would happen to those light rays after they reflect off the curved mirror?
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[answer] => 4
[description] => Reason for the Correct Answer:
Concave parabolic mirrors focus parallel light rays
Light rays parallel to the principal axis are focused towards the focal point of the mirror
Since the light rays will be focused toward the focal point, the light rays will converge at the previous location of the light bulb
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[each_answer] => A. They would be focused at point B
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[each_answer] => B. They would be reflected back our parallel to the principal axis since they were parallel to begin with
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[each_answer] => C. They would be focused at point C
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[each_answer] => D. They would be focused at the original location of the light bulb
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[559836|5] => D
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