magnetic field in a coil

You can ‘see’ magnetic fields using iron filings. You can measure the strength of magnetic fields using a magnetic field sensor connected to a computer. How, for example, does that field vary as you move through a coil? Is there a connection between the field and the distance moved through the coil?

What you need

Clamp stand, Helmholtz coils, leads, power supply, metre rule, interface, magnetic field sensor. Also your sensing software should allow you to enter distances at the keyboard – but it’s not too bad if not.

Setting up
Connect the magnetic field sensor to the interface. If the sensor is adjustable, set it to a fairly sensitive range such as 0-10 mT.
Start your sensing software. The software also needs to know that you will be entering distances, of between 0 and 100 cm, using the keyboard. While you are recording, you should be prompted to enter the distance you have moved the probe. (Not all sensing software can do this – so a way round this is to move the probe at a steady speed into the coil. This results in a graph that show magnetic field strength over time instead of distance. The shape of the graph however is pretty much the same). 

Start recording. Put the probe next to the coil and type in 0 for the distance. Move the probe 1cm into the coil. Type in 1 for the distance. Continue moving the probe and entering the distance each time.

Questions

How is increasing magnetic field shown on your graph?
How does the field strength change with distance?

How important is it to enter the distance along the coil via the keyboard?