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Example Lesson Scenario: Biomedical Engineering

 

Scenario: In her introductory Biomedical Engineering course, Jane is teaching her 40 students about refraction and how it applies to corrective lenses for vision. She wants students to learn how the design of corrective lenses are based on Snell’s Law of Refraction, which in turn is based on Fermat’s Principle.

By the end of her 90-minute lesson, Jane would like her students to be able to:

  1. Describe why myopia is a refractive disorder
  2. Differentiate between reflection and refraction
  3. State Fermat’s Principle
  4. Explain in their own words how Fermat’s Principle leads to the Law of Reflection
  5. Explain in their own words how Fermat’s Principle leads to Snell’s Law of Refraction
  6. Apply Snell’s Law of Refraction to determine the path of a given ray of light through a given lens
  7. Describe how lenses can correct for myopia.

 

This example contains 10 poll questions and uses the following poll types:

  • 3 x Multiple Choice
  • 1 x Word Cloud
  • 1 x Q&A
  • 1 x Rank Order
  • 3 x Clickable Image
  • 1 x Open-ended

Introduction to Refractive Disorders (20 minutes)

Jane begins her lesson with a case study of a young boy who has trouble viewing what his teacher writes on the blackboard, but is able to read a book that he is holding. Jane projects the anatomy of the eye and briefly describes the different parts of the eye and how incoming light rays are focused on the retina. She mentions light bending, but does not yet refer to it as refraction.

Jane then asks her class to diagnose the boy’s condition.

Question Type: Multiple Choice
Cognitive Process: Understand
Question: Which of the following is the most likely diagnosis of the young boy’s condition?

A. Astigmatism
B. Hyperopia
C. Myopia
D. Presbyopia

Rationale: While this question requires students to recall from their previous knowledge what these refractive disorders are, it additionally requires students to classify the boy’s condition based on the signs and symptoms described.

Many students select the correct answer, but not all students know what all the different terms mean. Jane asks for volunteers to define each term and explain why they think it is or is not the correct answer. She then confirms the correct answer.

Next, Jane asks her students to explain how myopia leads to near-sighted vision.

Question Type: Multiple Choice
Cognitive Process: Remember
Question: Myopia is also known as near or short-sightedness. What is the reason images are not focused on the retina?

A. The length of the eyeball from front to back is too long
B. The curvature of the cornea is too shallow
C. The lens of the eye is too thin

Rationale: At this point in the course, this question requires students to recall that short-sightedness is a refractive disorder that results in light focusing far in front of the retina because the eyeball is elongated. This question can be modified to have students deduce the reason by applying the law of refraction.

Jane explains that in the case of myopia, the light rays that travel from a distant object and enter the eye focus in front of the retina instead of on it. She then projects three images of eye anatomy that correspond to the three multiple choice options. Jane illustrates on the images how light rays traveling from distant objects and entering the eye fail to focus on the retina in all three cases. She then emphasizes that only when the length of the eyeball is too long, i.e., Answer A, do the light rays converge in front of the retina as opposed to behind it.

Jane then mentions that this bending of light is called refraction and that myopia and the other diagnoses are thus called refractive disorders.

Illustrating Reflection and Refraction with Demos (20 minutes)

Jane proceeds to perform demonstrations of reflection and refraction, each time asking students to predict the outcome. 

For reflection, she sets up a laser pointer to point at a mirror and asks students to predict where the light from the laser would end up.

Question Type: Clickable Image
Cognitive Process: Understand
Question: Where do you predict the light from the laser pointer will appear on the screen on the right? (Not drawn to scale)

 

Rationale: This question requires students to understand the Law of Reflection in order to generally predict the path of the given ray of light. While this could potentially be a multiple choice type poll, making it a clickable image removes any hints as to where the light may end up.

 

For refraction, she asks students to predict what the pencil would look like when it is partially submerged in water. 

Question Type: Clickable Image
Cognitive Process: Understand
Question: Where do you predict the viewer will see the sharp end of the pencil? (Not drawn to scale)

 

Rationale: This question requires students to understand Snell’s Law of Refraction in order to generally predict the path of the given ray of light. While this could potentially be a multiple choice type poll, making it a clickable image removes any hints to where the viewer will see the sharp end of the pencil.

 

To emphasize the point that refraction only occurs when light rays pass between media of differing refractive indices, Jane asks her students the following question:

Question Type: Rank Order
Cognitive Process: Remember
Question: How would you rank the following media according to their refractive indices, beginning with the lowest refractive index?

  1. Water at 20°C
  2. Air at STP
  3. Optical Crown Glass
  4. Polycarbonate
  5. Vacuum

Rationale: This question requires students to recall from their previous knowledge what the approximate refractive indices are in relation to each other. They may not know the specific indices for all the listed media, but this is a good learning opportunity for them to find out.

Exploring the Laws of Reflection and Refraction (20 minutes)

Having explained both the Law of Reflection and Snell’s Law of Refraction, Jane proceeds to ask her students to compare and contrast the two laws.

Question Type: Q&A
Cognitive Process: Analyze
Question: What do you think is the main difference between reflection and refraction?

Potential student responses:

  • Reflection occurs in the same medium while refraction occurs in two media.
  • For refraction to occur, the ray of light needs to pass from one medium to a medium with a different refractive index.
  • Refraction is the bending of light as it passes from one medium to another.
  • Reflection requires a reflective surface while refraction does not.
  • The angle of incidence is equal to the angle of reflection but not the angle of refraction.

Rationale: Students have to contrast reflection and refraction in order to generate as a group a list of differences between the two concepts. While there are a number of differences, students also need to decide what information is important and relevant to answering the question. The instructor can designate specific student responses for the class to vote up/down in order to determine the best answer. 

 

At this point, Jane mentions that both reflection and refraction can be understood using Fermat’s Principle. She describes Fermat’s principle and how it can be used to explain the concepts of reflection and refraction. She also alerts students to two videos on deriving the Law of Reflection and Snell’s Law of Refraction using Fermat’s principle that they should watch after class as it would help them with their homework assignment. Jane then asks students to share one word that they think best associates with Fermat’s Principle.

 

Question Type: Word Cloud
Cognitive Process: Remember
Question: What one word do you think best associates with Fermat’s Principle?
Possible student responses:

  • Fastest
  • Light
  • Reflection
  • Refraction
  • Time

Rationale: Fermat’s Principle is that light follows the path of least time. This is an opportunity for students to not only recall the central premise of the principle, which is the basis of both the Law of Reflection and Snell’s Law of Refraction, but for the instructor to know what students associate with this principle. By listening to why students chose specific words, the instructor can address any misconceptions that arise.

Correcting Refractive Disorders (25 minutes)

Jane then focuses on how lenses can be used to correct vision. She first demonstrates to her students how to sketch the approximate path of a ray of light that passes from air to a curved lens. She then asks students to predict the approximate path of a ray of light that passes from a curved lens to air.

Question Type: Clickable Image
Cognitive Process: Apply
Question: Where do you predict the ray of light will appear on the screen? (Not drawn to scale)

Rationale: This question requires students to apply the light ray-drawing procedure based on Snell’s Law of Refraction to a curved surface in order to generally predict the path of the given ray of light. While this could potentially be a multiple choice type poll, making it a clickable image removes any hints to where the ray of light will appear on the screen.

 

After explaining to the class how to trace the path of a ray of light traveling from a curved lens into air using Snell’s Law of Refraction, Jane has them apply that skill to different shapes of lenses to determine which would be best suited to correct for myopia. For this activity, she has them first work individually for five minutes, then pair up, and finally call on students to draw the paths for each lens on the chalkboard.

 

Question Type: Multiple Choice
Cognitive Process: Evaluate
Question: Which of the following lenses would be best suited to correct for myopia? (Not drawn to scale)

A. Biconcave

 

B. Convex-concave

C. Concave-convex

D. Biconvex

Rationale: This question requires students to apply Snell’s Law of Refraction to two consecutive curved surfaces in order to generally predict the path of the given ray of light. They then have to evaluate the lenses to determine the one that is best suited for myopia correction.

Reflection on Learning (5 minutes)

Finally, five minutes before the end of class, Jane has her students answer two quick reflective questions.

Question Type: Open-ended
Cognitive Process: Analyze
Question 1:
What is your main takeaway from today’s class session? 
Question 2: What is one question you have from today’s class session?

Rationale: These two questions require students to reflect on the class lesson to determine what their main takeaway is and what questions they still have. This is an opportunity for students to practice their metacognitive skills to understand what and how well they learned from the class session, while the responses give the instructor insights into what students are thinking.

 

After class, Jane reviews the open-ended responses to look for what students are taking away from her lesson, and whether these align with her learning objectives for her students. She notes down the main points of the lesson that most students did not mention so she can highlight them again later. Jane also scans through the list of student questions and identifies those that multiple students bring up. She compiles these questions in an announcement on CourseWorks (Canvas), includes her responses and resources (specific pages of textbook, link to article, etc.) for students to follow up on, and reminds students to attend her office hours if they still have questions. As she has told the class previously, she also selects the most important questions for use in an upcoming low stakes quiz in class as well as for a practice exam.