administration student task rubric student work technical quality
Snell's Law

Grade 9-12 Performance Task
Developed by: New York State Education Department (NYSED)
University of Buffalo and NORC (1991, revised 1993)

Task-Specific Scoring Criteria for Physics Task #4: Snell's Law:


1. Statement of hypothesis Not required for this task
- Effect linked to variable  
- Directionality of effect  
- Expected effect/change  
- Independent variable  
- Dependent variable  
2. Procedures for investigation  
- Detailed procedure/experimentally feasible From the measured angles, calculate n = sin i/sin r
- Sequence to plan Do experiment with several angles of incidence
- General strategy Measure the angles of incidence and refraction and check in value.
- Safety procedures *
- Use of equipment/diagram Identify components of equipment; suggest assembly of set-up.
3. Plan for recording and organizing observations/data  
- Space for manipulation of data or qualitative description Construct a table with columns for i, r, sin i, sin r, n.
- Matched to plan Data table matches procedure in step 2.
- Organized sequentially *
- Labelled fully (units included) Angle i and r and index of refraction dimensionless.
- Variables identified Angles of incidence and refraction and index of refraction.



4. Quality of observations/data  
- Consistent data As angle i increases, angle r increases.
- Accurate measurements, observations Angles of incidence and angles of refraction measured to the nearest degree. Angles of r between 8 degrees and 40 degrees.
- Completed data table 6 pairs of measurements with sine values.
- Correct units Degrees for angle r; sin i and sin r are dimensionless.
- Qualitative description *
5. Graph  
- Curve is appropriate to data trend Graph of sin i vs sin r is a straight line (best fit)
- Points plotted accurately Points correspond to measured data.
- Appropriate scale Sin i range (0.1 - 0.9); sin r range (0.1 - 0.9).
- Axes labelled with variabls Labels are placed on graph
- Variables placed on correct axes Sin i on y; sin r on x
6. Calculations  
- Calculated accurately Calculated accurately with appropriate use of significant figures.
- Substituted correctly into relationship Calculate slope as n= (delta sin i)/(delta sin r). Points used should be on the best fit line.
- Relationship stated or implied *
- Units used correctly n is dimensionless
- Use all data available Use the best fit line to calculate the slope with chosen points on the straight line far from each other.
7. Conclusion  
- Consistent with scientific principle Calculation consistent with index of refraction taken from data provided.
- Sources of error *
- Consistent with data Conclusion is consistent with student's experimental data.
- Relationship among variables stated *
- Variables stated in conclusion Index of refraction.


* These elements were not scored in this task; a "holistic" scoring approach was utilized so that the other four elements had a total value of 5 points.


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