Training to Use the Scientific Method in a First-Year Physics Laboratory: A Case Study

Abstract

In this work, a specific implementation of a so-called experimental or open-ended laboratory is proposed and evaluated. Keeping in mind the scheduling limitations imposed by the context, first-year engineering physics laboratory practices have been revised in order to facilitate acquisition of the skills that are required in the experimental work. These skills concern different conceptual and procedural abilities related to designing experiments, taking measurements, analyzing the results and reporting properly the whole process. The employed approach is described, and the achieved results are evaluated by a series of tests at the beginning and end of the academic year. Additionally, the students’ laboratory reports are used to quantify the evolution of acquiring these scientific skills. The evaluation of the results obtained from the aforementioned tests and laboratory reports gives enlightening information about students’ apprehension of the experimental method itself, as well as the difficulties they find in each of the different, complex tasks that they must carry out during this process.

Appendices

Appendix 1

See Table 2.

Table 2 List of experiment guides included in the lab-program and distribution during the academic year

Example of Experiment Guide

Magnetic Force on Currents

Materials List

• A current balance complemented by:

  • Six Current Loop PC boards

  • Magnet Assembly with six magnets

  • Complement to change the angular position

• DC power supply capable of supplying up to 5 A

• Rheostat to control current intensity

• DC ammeter capable of measuring up to 5 A

• Balance capable of measuring forces with an accuracy of 0.01 g mass equivalent

• Lab stand

• Hook-up wires with banana plug connectors

Goal

Analyze the characteristics of the magnetic force that acts on a conductor while a current is flowing through it. Demonstrate which factors have influence over the magnetic forces.

Advice

• Read the information concerning the equipment in the section ‘Description of equipment and materials’

• Analyze the current loops and the complement for changing the angular position: what is the difference between them? What will be the direction of the current?

• What is the relationship between the magnetic force and the measurement done with the balance?

• Before plugging in the DC power supply, check that the control button is in its leftmost position. The resistance in the rheostat should be maximum at the beginning of the experiment.

• It is advisable to change the angles more than 15° from one measurement to the next one.

Be careful
The maximum intensity I that the angular complement admits is 2 A.
If you surpass this value, the complement can break!

Some Tips for the Analysis

• 1. What is the influence of the orientation over the magnetic force? And the value of the intensity? Is there any other factor that should be taken into account?

• 2. Compare your results with theory.

Appendix 2: Assessment Tool

See Table 3.

Table 3 Items taken into consideration for the assessment of the lab reports

Appendix 3: General Guide for Conducting Laboratory Practices

• 1. What is the purpose of this experiment?

• 2. Summarize your knowledge about this topic.

• 3. Design your experiment:

  • 3.1 What do you think that is going to happen? How will the system behave? Explain your hypotheses.

  • 3.2 Taking into account the objective of the experiment and your hypotheses, which magnitudes will you measure? Why and what for?

  • 3.3 Describe the method you will use (make as many diagrams as you need in order to make the description clear) and explain briefly how you will achieve your objective using that method.

  • 3.4 How will you explain your results? Evaluate the advantages and drawbacks of the different options: graphs and curve fittings, tables of results, simple direct measurements. Taking into account this evaluation, argue your choice.

• 4. Take your measurements following the method you have proposed. Show clearly the most important data of the experiment and the results. If you analyze more than one case, show the results without mixing them.

• 5. Analysis of the results

  Analyze in all the cases:

  • 5.1 Do the results agree with the proposed hypotheses? What is your next decision, in that case?

  • 5.2 Calculations: What are the experimental values of the magnitudes you should measure? And the estimate of the experimental error you have made?

  • 5.3 In view of the results, what can be concluded? Take into account the information that has been proposed in the experiment guide. Do you consider that the experimental measurement has finished or would you prefer to start again using another method? Can you improve your method?

• 6. Report

  Start writing the report on the performed work and explain the results and conclusions.

Appendix 4: Preliminary Test

• 1. When it is said that Physics is an experimental science, what does it mean?

  • □ It means that Physics can be applied to developing new technology.

  • □ It means that Physics is based on experimental data.

  • □ It means that we sometimes go to the lab with the aim of verifying the theory and understanding it better.

  • □ It means that physicists usually do experiments in the lab.

• 2. In your opinion, what is “to take a measurement”?

  • □ To assemble the devices, switch them on and take the measurement.

  • □ To verify whether a theoretical law is obeyed or not.

  • □ To verify whether a hypothesis is true or not using experimental data.

  • □ To perform measurements changing many parameters, in order to observe how the result changes.

• 3. What do you think a measurement is for?

  • □ To quantify the small error that always occurs in a measurement.

  • □ To prove that the theory is correct.

  • □ To find something previously unknown.

  • □ To verify the validity of the hypothesis and its applicability limits.

• 4. What is the difference between a mathematical law or function and a physical one?

  • □ Mathematical laws are deduced using logical arguments while physical ones are deduced experimentally.

  • □ Physical laws are a particular case of mathematical ones.

  • □ Mathematical functions are much more complicated than physical ones.

  • □ Mathematical laws are always fulfilled, while physical ones are not.

• 5. What does the experimental error mean on a physical measurement?

  • □ It means that the measurement device fails.

  • □ It quantifies the difference between the true value and the value obtained from the experimental measurement.

  • □ The error always goes with the result, if somebody doubts its validity.

  • □ It means that the initial hypothesis was wrong.

• 6. Which is the language we use to express what we measure in the lab?

  • □ English.

  • □ The letters of the Greek alphabet.

  • □ The mathematical language.

  • □ The mathematical equations of what we conclude experimentally.

Appendix 5: Final Questionnaire

• 1. When it is said that Physics is an experimental science, what does it mean?

  • □ It means that Physics can be applied to developing new technology.

  • □ It means that Physics is based on experimental data.

  • □ It means that we sometimes go to the lab with the aim of verifying the theory and understanding it better.

  • □ It means that physicists usually do experiments in the lab.

• 2. In your opinion, what is “to take a measurement”?

  • □ To assemble the devices, switch them on and take the measurement.

  • □ To verify whether a theoretical law is obeyed or not.

  • □ To verify whether a hypothesis is true or not using experimental data.

  • □ To perform measurements changing many parameters, in order to observe how the result changes.

• 3. What do you think a measurement is for?

  • □ To quantify the small error that always occurs in a measurement.

  • □ To prove that the theory is correct.

  • □ To find something previously unknown.

  • □ To verify the validity of the hypothesis and its applicability limits.

• 4. What is the difference between a mathematical law or function and a physical one?

  • □ Mathematical laws are deduced using logical arguments while physical ones are deduced experimentally.

  • □ Physical laws are a particular case of mathematical ones.

  • □ Mathematical functions are much more complicated than physical ones.

  • □ Mathematical laws are always fulfilled, while physical ones are not.

• 5. What does the experimental error mean on a physical measurement?

  • □ It means that the measurement device fails.

  • □ It quantifies the difference between the true value and the value obtained from the experimental measurement.

  • □ The error always goes with the result, if somebody doubts its validity.

  • □ It means that the initial hypothesis was wrong.

• 6. Which is the language we use to express what we measure in the lab?

  • □ English.

  • □ The letters of the Greek alphabet.

  • □ The mathematical language.

  • □ The mathematical equations of what we conclude experimentally.

• 7. A group of students is studying the charging and discharging processes of a capacitor in the lab. They assemble a RC circuit and after connecting it to a power supply, they measure the potential difference between the terminals as a function of the time. When they were completing their lab report, they doubt about the most appropriate graph and argue their different opinions. Which is, in your opinion, the best graph to explain the experimental data? Choose the correct answer and reason your choice.

  

  Reason your answer:

• 8. The objective of the next experimental procedure is to analyze what happens when two carts that travel in a one-dimensional guide-rail collide (see figure). In particular, the interest is focused on the kinetic energy of the system.

The different working groups start arguing their different proposals as follows:

• (a) The total kinetic energy of both carts won´t be the same, due to the forces that appear during the interaction.

• (b) The masses and velocities of the carts are variables that must be measured.

• (c) The collisions are divided into elastic and inelastic ones.

• (d) If the masses are equal, the collision is always elastic.

• (e) If the mass of one of the carts is increased, the collision will be more inelastic.

• (f) If the total kinetic energy of the system is conserved, the collision will be elastic.

From all these proposals, which are real working-hypotheses? Reason your answer.

• 9. Let’s suppose now that with the same previous experimental set–up, we want to analyze what happens with the linear momentum of the system, so we decide to study whether the following working hypothesis is verified or not: ‘In every collision the linear momentum of the system is conserved’. To assemble this experiment, you have two carts, a guide-rail, additional masses and photocells to measure the velocities of the carts. Describe the experimental design you will propose to verify the working hypothesis.

• 10. A working group of students assembles an experimental setup to measure the magnetic field (B) produced in a double-winding solenoid. They want to know what factors will change the value of B when they insert the sensor in the middle of the solenoid. To clarify this, they take the following measurements:

  Test	Distance from the center, x (cm)	Current I (A)	Magnetic field B, (gauss)
  1	0	0.40	6.6
  2	0	0.50	7.4
  3	0	0.80	9.4
  4	20	0.80	6.2
  5	20	0.85	6.4

From this group of measurements:

• (a) Which of them could be used to analyze the dependence of B with I?

• (b) Is it possible to deduce if B is proportional to I?

• (c) Can we conclude that the lateral coils of the solenoid produce a smaller magnetic field than those in the center?

• 11. A working group of students has done the next experimental practice. They measure the magnetic force that undergoes a segment of a certain length of an electric circuit when it is inserted in a constant magnetic field and the current intensity that circulates on it is changed. These are the experimental data:

  I (A)	Fm (N)
  0.4	0.09
  0.5	0.12
  0.6	0.14
  0.7	0.16
  0.8	0.19
  0.9	0.21

  In the final report appears the following: ‘The magnetic force that undergoes the circuit of length depends on the current intensity and the magnetic field’. What do you think about this statement?

  

  Why do you choose this answer?