Two students use a digital Hall probe connected to a Tesla meter to investigate how the magnetic flux density along the central axis of a small circular coil varies with distance. The coil is connected to a stable DC power supply. The students position the sensor at various axial distances, zzz, from the centre of the coil. The Tesla meter displays integer values in millitesla (mT\text{mT}mT).
The table below shows their results:
Axial distance, z (mm)Magnetic flux density (mT)088105420283015408504601701801 \begin{array}{|c|c|} \hline \textbf{Axial distance, } z \text{ \textbf{(mm)}} & \textbf{Magnetic flux density (mT)} \\ \hline 0 & 88 \\ 10 & 54 \\ 20 & 28 \\ 30 & 15 \\ 40 & 8 \\ 50 & 4 \\ 60 & 1 \\ 70 & 1 \\ 80 & 1 \\ \hline \end{array} Axial distance, z (mm)01020304050607080Magnetic flux density (mT)8854281584111Each student displays the results using a different graphical representation:
Discuss which graph (Graph C or Graph D) is best for representing this type of data.
Suggest how the students could improve the accuracy of their axial distance measurement.
Suggest why the reading on the Tesla meter remains constant at 1 mT1\text{ mT}1 mT for the final three readings.
The students modify their apparatus to investigate how effective different metal sheets are at shielding magnetic fields. They place a thin sheet of a test metal between the circular coil and the Hall probe sensor.
Describe how the students should control the variables in this modified investigation.
