Helping students learn to design experiments in an large ...

Helping students learn to design experiments in an large-enrollment introductory laboratory class AAPT National Meeting, Sacramento, August 2004 Sahana Murthy, Eugenia Etkina, Michael Gentile, Aaron Warren, Alan Van Heuvelen Rutgers University, New Jersey http://paer.rutgers.edu/scientificabilities Supported in part by NSF Grant DUE #0241078 What are design tasks? Students design experiments to • Investigate new phenomena: Observation experiment Example: Design an experiment to devise a rule for the force a magnet exerts on a moving charge. • Test a hypothesis: Testing experiment Example: Your friend says that as current flows through a circuit, it is used up by the elements of the circuit. Design an experiment to test this hypothesis. • Solve a practical problem: Application experiment Example: Design experiments to determine the thickness of a strand of your hair using two independent methods, one of which must involve ideas about diffraction. Features of design tasks • Part of ISLE cycle: Observation, testing or application experiment • Divergent thinking-- two independent methods to solve problem • Open ended, ill-defined • Need to perform additional experiments or informed estimates to solve task • Task can involve more than one topic in physics • Qualitative and quantitative experiments Implementation • • • • • • • • • • Large enrollment class -- 450 students Algebra-based class, health science majors Lab class accompanies lecture class 20 lab sections, 6 TAs TAs not involved in PER activities Training -- TAs perform mock design tasks Collaboration with lab coordinator Design tasks given in 2nd semester of course One design task per lab Students perform experiments and write reports in a 3hour laboratory Example: Magnetism Observation experiment Design an experiment to devise a rule for the direction of the force a magnet exerts on a moving charge. Equipment: Bar magnet, Cathode Ray Oscilloscope. a) b) c) d) Devise and write an outline of your procedure. Draw a labeled diagram. List the assumptions that you made. Perform the experiment and record your observations. Make a table if necessary. e) What patterns did you find from your data? f) Devise an explanation for the pattern. g) Devise a rule for the direction of force that the magnet exerts on the moving charge. Example: Magnetism Testing experiment Design an experiment to test the rule you developed about the direction of force a magnet exerts on a moving charge. Equipment: Strong horseshoe magnet, power supply, wire. a) b) c) d) e) f) State the rule that you are going to test. Devise and write an outline of your procedure to test the rule. Draw a labeled diagram. List the assumptions you made. Make your prediction using the rule and the planned experiment. Perform the experiments and record the results. Make a table if necessary. g) Use hypothetico-deducto reasoning with the arguments and evidence for testing your rule. Is your prediction confirmed? h) What is your judgment about the rule? Application experiment Design two independent experiments to determine the width of a strand of your hair. One method must involve ideas of diffraction. Equipment: Laser pointer, meter stick, holder for hair, screen. Devise and write an outline of the procedure. Draw a labeled diagram of your experiment. Write the mathematical procedure you will use. Write how you will measure the physical quantities you need. List the assumptions are you making in your design. Perform the experiment. Record your measurements. Calculate the thickness based on your procedure and measurements. What are possible experimental uncertainties? How could you minimize them? Evaluate the effect of the uncertainties on the data. i) When finished both experiments, compare the two values for the thickness. What are possible reasons for the difference? a) b) c) d) e) f) g) h) Example: Optics Example: Specific heat Application experiment Design two independent experiments to determine the specific heat of the given rock. Equipment: water, heater, Styrofoam containers, balance, thermometer and timer. a) b) c) d) e) f) g) Devise and write an outline of the procedure. Draw a labeled diagram of your experimental set-up. Write down the mathematical procedure you will use. List the assumptions you made. How could they affect your results? Write down how you will measure the physical quantities you need. List sources of experimental uncertainty. How will you minimize them? Perform the experiment and record your measurements. Make a table for your measurements, if necessary. h) Calculate the specific heat, based on your procedure and measurements. i) After you have done both experiments, compare the two outcomes. What are possible reasons for the difference? Example: Thermodynamics Application experiment Design an experiment to determine if the power rating of a water heater is reasonable. Equipment: Immersion heater, stopwatch, thermometer, Styrofoam cup and lid. a) b) c) d) e) f) g) h) i) j) Devise a procedure and write down an outline. Draw a clearly labeled diagram. Write the mathematical procedure you will use. Write down how you will measure the physical quantities you need. List the assumptions are you made. How could these affect the result? Perform the experiment. Record your measurements in an appropriate format. List sources of experimental uncertainties. How could you minimize them? Do the necessary calculations. Make a judgment about whether the power rating is reasonable. Suggest specific improvements in the experimental design. Example: Newton’s Laws Application experiment Design at least two independent experiments to determine the coefficient of static friction between your shoe and the carpet. Equipment; Spring scale, ruler, protractor, tape, string, assortment of blocks, hanger, pulley, clamp, force probe. a) Devise a procedure and write down an outline. b) Draw a clearly labeled diagram. c) Draw a free-body diagram for the system with a set of coordinate axes. Use the free-body diagram to devise a mathematical procedure. d) List the assumptions you made. How could these affect the result? e) List sources of experimental uncertainty? How could you minimize them? f) Perform the experiment and record your observations.Make a table if necessary. g) Do the calculations. What is the outcome of your experiment? h) When finished with both experiments, compare the two values you obtained for the coefficient of static friction. What are possible reasons for the difference? Development of rubrics • • • • Rubrics based on scientific abilities* Rubrics match guidelines in experiments 90% Inter-rater reliability with Rutgers PAER group Can be used for  Research on development and assessment of scientific abilities  Grading lab reports by teachers  Self-assessment of lab reports by students * Etkina, E., “Developing and assessing scientific abilities in an introductory physics course”, AAPT Announcer, Vol.33, No.4, P.85 (2004). Research and Findings • 35 students in sample • Randomly selected from 4 sections • Scored student responses from week 3 (initial) and week 10 (final) • Found significant improvement in some scientific abilities Ability 1: To design a reliable experiment that solves the problem 25 20 15 10 5 0 INITIAL Score 0 Score 1 FINAL Score 2 Score 3 Ability 2: To choose a prooductive mathematical procedure 25 20 15 10 5 0 INITIAL Score 0 Score 1 FINAL Score 2 Score 3 Ability 3: To communicate details of the experiment completely 25 20 15 10 5 0 INITIAL Score 0 Score 1 FINAL Score 2 Score 3 25 20 15 10 5 0 Ability 4: To evaluate the effects of experimental uncertianties INITIAL Score 0 Score 1 FINAL Score 2 Score 3 Examples of design tasks and scientific ability rubrics are at: http://paer.rutgers.edu:/scientificabilities Sample student response and scores on scientific abilities Ability Score To design a reliable experiment 3 that solves the problem To choose a productive mathe-matical procedure for solving 3 an experimental problem To make a judgment about the 2 results of the experiment To communicate the details of an 2 experimental procedure clearly and completely To identify the assumptions made 1 in using the chosen procedure To evaluate specifically how 2 experimental uncertainties may affect the data Conclusions • Possible to implement and assess open-ended design tasks in large enrollment class • Students’ scientific abilities improved • Assessment rubrics serve as goals for writing new design tasks Further work •Students will be provided rubrics for self-assessment •Controlled experiment to test if guidelines in rubric caused improvement in students’ abilities •Correlation between students’ scores on abilities and test scores?