1. Formulate hypotheses that allow you to answer the initial questions.

2. Plan an investigation by which you can verify your hypotheses (describe in detail all the steps, including study variables and the equipment and materials needed).

3. Carry out your investigation.

4. Organize the data collected. 

5. Analyze and explain your data. 

6. Compare your results with the data shown in Table 1 and conclude about your hypotheses and give an answer to the proposed initial question. 

Table 1- Summary of the limits recommended by ICNIRP (source: adapted from the table available in https://www.icnirp.org/cms/upload/publications/ICNIRPLFqdl.pdf)

1. Probably, most of the students will answer that, at school, they are not exposed to average magnetic field values higher than the reference values. 

2. Students should plan an activity that allows them to measure the density of the magnetic field in different places of the school. To do this, students should take in account how and where the measurements must be done. Students should define different measurement stations in different locations in the school, and use their cell phones with an application that allows them to take measurements, such as the Phyphox app. 

3. Students must register around 15 values ​​per station. In addition, they must have the opportunity to measure significantly different magnetic field values in at least at one of the stations.

 4. It is intended that students, in the classroom, determine the average value of the 15 readings, for each station, respecting the number of significant digits. Then, it is intended that they organize the results, that is, the average values ​​of the magnetic field, with the respective stations.

5. Students can search for information to recognize that background "noise" observed in the cell phone represents the Earth's magnetic field (represented by the lower average values detected in most stations). If the students notice any peak in the measurements, they should state that this may be due to the proximity of a much higher electric current passage or the existence of a magnet such as in a car engine.

6. Through the data of Table 1 and the collected ones, students should conclude that, at school, they are not subject to values of magnetic field higher than the reference value, as they probably hypothesized. Students should also conclude that the value of the Earth's magnetic field should be close to the noise values obtained in all groups, in most stations, and that the Earth's magnetic field has values between 20 and 60 μT. Thus, in addition to the values of the average magnetic field in the school being lower than the reference values, these values are very close to the Earth's magnetic field.

This task is suitable for high-school students.

The IBL cycle begins with an initial question, based on which students have the opportunity to formulate hypotheses and plan an activity that will allow them to confirm or refute the hypotheses, as well as to answer the initial question. 
Regarding the activity that students plan, teachers may suggest locations for the different measurement stations, allowing students to observe peaks in the measurements of the magnetic field. 
Students should work as a group, and the teacher should play the role of facilitator of learning, guiding students in their investigations and asking students about their ideas.