PALS - Rubric

Snell's Law

Rubric

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:

PART A: EXPERIMENT DESIGN

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.

PART B: EXPERIMENT REPORT

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.