Il Museo di Fisica di Sardegna

	Interactive experiments and exhibits News Events F G C
	Introduction Arago's disk Oersted's experiment Electromagnetic induction The Foucault current Electrodynamic actions Coils, solenoids and other things Measurement of a magnetic field Magnetic properties of materials Levitation experiment And if there's no variation in flow? The rotating magnetic field High frequency fields Photos	INTERACTIVE EXPERIMENTS AND EXHIBITS MEASUREMENT OF MAGNETIC FIELDS There are many ways of measuring magnetic fields. The classic one is to use the electromotor force induced in a probe bobbin of known characteristics which is moved quickly in the field. It can be demonstrated that with all the constants of the system known, a charge meter, for example a ballistic galvanometer or, in a more up to date way, a charge amplifier, supplies an absolute measure of the field. The method we have chosen is based on the recent availability of low-cost Hall Effect probes with the proper characteristics. Below we see the circuit of the instrument designed so as to facilitate its construction. Here are the probes of the instrument: The one on the left is for transverse fields while the one on the right is for axial fields. The dimensions of the sensitive part are approximately 3 x 3 mm² The value of the magnetic field at that point is shown on the tester. Among other things, the instrument is sensitive enough to give a precise indication of the north-south direction of the earth’s magnetic field, which is approximately 0.40 Gauss at our latitude. Here we have everything ready for verification of the theory: As we have seen, the field inside the solenoid and distant from the mouth is quite uniform in the transverse direction To see a measurement, click on the photo And here is this instrument in the measurement of the field around a straight electrified wire to verify Biot and Savart’s Law. To see click on the photo The diagram of the apparatus: The nominal sensitivity given for the Hall probe used is 3.125 mV/Gauss, with a measurable maximum of about 800 Gauss = 0.08 Tesla. This circuit has ranges of 1, 10, 100, 1000 Gauss at the bottom scale of 1V of the tester, thus with a tester that indicates 10 mV, we have appreciable variations in the continuous fields of 10 mGauss.