When current passes through a solenoid a magnetic field is produced. The purpose of this experiment is to qualitatively study how the field varies in different parts of the solenoid and to investigate the factors that effect the magnetic field produced inside a solenoid. According to Ampère’s Law the magnetic field in the interior of a long solenoid is

whereis the permeability of free space, n is the number of coils per unit length and, I is the current passing through the solenoid. In this experiment a metal slinky is used to model a solenoid as this will allow you to vary both the current and the coils per unit length.

Use the Vernier Magnetic Field Sensor attached to the Lab Pros to measure the magnetic field with the switch on the sensor set to low. Stretch the slinky so that the coils of the slinky are not touching. Attach the leads of the power supply to each end of the slinky. Put a multimeter set to read up to 10 amps in series with the slinky. Turn on the power supply when you are ready to make measurements. You may use currents up to 2.0 A but do not leave the circuit in this state for any length of time as the slinky is liable to get hot.

First make a survey of the magnetic field strength both inside and outside of the solenoid. Determine if the direction of the magnetic field agrees with what you expect. Remember to account for the magnetic field of the earth. Then design an experiment that will allow you to investigate the relationship between magnetic field inside the solenoid and each of the important variables: current and turns per unit length. Use graphical analysis to test Ampère’s proposed relationship and use these graphs to determine the permeability of free space. Compare your results with the literature value and evaluate the experiment.