Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

How to easily, using standard DIY equipment measure the strength of magnetic field generated by a permanent magnet?

Narrowing down the "loose language" of the above:

strength of magnetic field: either flux density B at given point relative to the magnet or magnetic flux ΦB over area enclosed by a loop made of wire - whichever will be easier to measure, either of those is fine.

standard DIY equipment: commonly found household items, rudimentary tinkering tools. Soldering tools, multimeter, simple electronic parts, or maybe an easy to make spring-based dynamometer - anything of this class of complexity.

The distance of measurement is such that the field is easily noticeable through simplest methods e.g. another magnet held in hand exerts perceptible force - distance of maybe 5cm away at most.

The measurement doesn't need to be very accurate - error of order of 50% is quite acceptable. Simplicity is preferred over accuracy.

Rationale: trying to estimate what coil I need to generate sufficient amount of power to light a LED with a frictionless generator based on that magnet (knowing speed of movement of the magnet and location of the coil relative to the path of the magnet). If you know other simple methods of doing that (without need for measuring the field), they are most welcome them too.

share|improve this question
add comment

3 Answers

up vote 1 down vote accepted

For what it's worth: http://www.coolmagnetman.com/magmeter.htm - a home-made device based on a Hall effect device - for about $40.

share|improve this answer
That's pretty nice - I'll accept if nobody comes up with something even more simple. –  SF. Dec 8 '12 at 21:08
add comment

The easiest method is to put a magnetic compass on one of the magnet's axes of symmetry, and orient the compass and magnet such that the magnet's field is perpendicular to the earth's. Then the tangent of the deflection angle is equal to the ratio of the fields.

share|improve this answer
That's nifty, although probably beter suited for weaker fields. Still - to know the absolute value of the field from the ratio I should know the local strength of earth's magnetic field. How would I go about finding it? –  SF. May 15 '13 at 7:44
add comment

Check out this explanation of http://en.wikipedia.org/wiki/Magnetometer#Fluxgate_magnetometer :


share|improve this answer
This needs a few words about the described device or it is just an outgoing like which is discouraged in answered. –  dmckee Dec 8 '12 at 18:44
While the idea behind the device is very neat, I'm not quite sure how to go about the driving circuit other than piecing something together on 555. Alternatively, pick a tiny transformer, run 230V AC through primary in line with some load, short the secondary circuit with a non-electrolitic capacitor and measure the voltage on the capacitor. Still, how to calibrate that? (at home!) –  SF. Dec 8 '12 at 21:15
add comment

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.