A light ray travels through air in a straight line until it hits the surface of a piece of clear glass, as shown in the diagram below.
The DOE published sample answers to this question to illustrate how the questions are graded. These answer are shown below. Regrettably, they also show the inadequacy of the grading process.
First, the question is quite confusing. Its purpose is to test student's knowledge of reflection and refraction. The hoped-for answer would have one drawing showing reflection and the other showing refraction. However, these phenomena are inseparable – it is not possible to have one without the other unless the student mentions linearly polarized light or Brewster angle. This means that one drawing should show both reflection and refraction. A knowledgeable student may have difficulties in coming up with the second drawing. If he really knows optics, he may show birefringent refraction in the second drawing. Unfortunately, this may result in a lower grade because it is unlikely that the grader knows what birefringent refraction is (a third of the graders don't even have a college degree).
The "Score Point 4" example has an incorrect drawing for the refraction of light – the light does not reverse its direction. To receive a 4, the rubric states that the response must indicate a thorough understanding of the properties of light and this is clearly not the case here.
The "Score Point 3" example has an equally incorrect drawing for the refraction of light. It shows both refraction and reflection, like in the "Score Point 4" example, but also introduces the concept of spectral separation. Perhaps this student knows more than the student who got 4 points.
The difference between the scores for these two examples is probably associated with part (b). The student with the higher score mentions refraction in connection with contact lenses while the student with the lower score does not show how spectral separation is used and his drawings do not show this phenomenon.
Both students understand reflection. Both got the refraction wrong. The difference is not based on the knowledge of these properties of light but on how well the students can follow instructions. The student with the higher score is good in taking tests, while the other student may know more, but is disorganized and under pressure of testing, lost his train of thought.
|
Score |
Description |
|
4 |
The response demonstrates thorough understanding of the properties of light. The response includes two drawings that illustrate what could happen to the ray of light and completely describes an example of a way people make use of each property of light. |
|
3 |
The response demonstrates general understanding of the properties of light. The response includes drawings that illustrate what could happen to the ray of light and describes in broad terms an example of a way people make use of each property of light. |
|
2 |
The response demonstrates simplistic understanding of the properties of light. The response includes drawings that illustrate what could happen to the ray of light and/or describes an example of a way people make use of each property of light. |
|
1 |
The response demonstrates minimal understanding of the properties of light. The response includes a drawing that illustrates what could happen to the ray of light or describes an example of a way people make use of each property of light. |
|
0 |
The response is incorrect or contains some correct work that is irrelevant to the skill or concept being measured. |
