I just had a look at the data of our latest experiment assignment for our students. Just like in our previous collective measurement of pendulum frequencies, the students were supposed to submit their results through an online form, so we can combine all the data to test a model that will be discussed in an upcoming lecture. This time, they should measure the magnetic field generated by a current loop.
Since we could not expect that every student has got an adjustable current available, we instructed them to simply use an AA battery (non rechargeable, non Lithium, etc. for safety reasons) and connect it to any cable (like the USB cable in the picture above). After finding the location of the magnetometer in their phones, they simply should create a loop with the magnetometer in its center and measure the change in the magnetic field perpendicular to this loop. Repeat five times with varying radius and submit the results:
Since we do not know the actual current used in this experiment (at 1.5V this still depends on the cable and the battery’s internal resistance), we told them to include one measurement at a radius of 5cm and plotted the ratio B(r)/B(5cm) of the B field at any radius to the one at 5cm, to eliminate this unknown. Also, the plot only shows the absolute value as some students submitted negative changes.
I am quite satisfied with the results and am looking forward to the lecture in which we can presented the collective data to the students.