Magnetic Field in a Coil

Exploring the magnetic field in a coil

You can 'see' magnetic fields using iron filings. You can measure 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

magndist.jpg (13347 bytes)

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

Set up the apparatus as shown. 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 - it may recognise the sensor automatically but if not set up the software to do so.
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 an alternative approach is given here:

	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.
	Start recording. Move the probe at a steady speed into the coil.

Questions

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

Teacher question

How important is it to enter the distance along the coil via the keyboard? Can't you just move the probe steadily? Click here to respond.

This activity was adapted by Roger Frost from The IT in Science book of Data logging and Control. This page is � IT in Science. It may be reproduced only for use within your school.