It is formed by a coil with an horizontal axle, that at the centre possess a compass able to turn in the horizontal plane. The active turns of the coil can be selected by the experimenter without moving contacts.

The device is oriented with the direction Nord- South perpendicular to the coil axle. When a direct electric current of known intensity I circulates through a group of N turns, a corresponding magnetic field is produced in the compass area. If this field is strong enough, the compass needle is deviated from the North-South direction and we will be able to measure the deviation angle (tangent compass). The Earth magnetic field acts as a recuperation force.

To produce an appropriate direct current of controlled intensity it is recommended the Potentiostat 5500.1, able to supply a stabilised current of approximately 400 mA.

2. Didactic utility of the instrument

The device permits the student to deep into the general concept of force field and, specially, of magnetic field. It allows to work from the semiqualitative level of the magnetic effect of an electric current to a more advanced levels. It allows the familiarity of the student with the magnetic fields produced by electric currents. In particular it allows verify the law:

it is: a current of intensity I that flow through a coil of radius R and N turns creates a magnetic field that is oriented according to the coil axle (ue direction), proportional to I an N and inversely proportional to R. We also can consider a more exact model of the created field at the coil inner that takes into account its width.



The instrument can be integrated into an informatic system of data acquisition by the current intensity; the number of turns and needle deviation angle should be introduced by keyboard.

The main didactic utility of the instrument is the following:

2.1. Experimental evaluation of the Earth magnetic field

When the needle turned angle will be 45º, the induced force of the created magnetic field will equate the force of the Earth magnetic field (being more exact: the horizontal component of the Earth magnetic field at the place of measurement) from the theoretical calculation

2.2. Field variation with current intensity

By modifying the flowing electric current we can modify the magnetic field and therefore the turned angle by the needle. Taking as basis the Earth magnetic field- calculated or derived from literature for the measuring place-, we can compare theoretical and experimental results.

2.3. Field variation width the number of turns

By modifying the active number of coil turns and maintaining the electrical intensity at constant level, we can study the created field in function of turn number.

2.4. Measurement uncertainty

Uncertainty calculation (experimental error to be spected) is included for advanced students.

3. Documentation

An application manual is supplied as documentation of the exercises with pedagogical orientation in order to facilitate the work of the professor and to guide the student practice.

3.1. User Manual

3.2. Applications directly to be done

PRA4.2/01-e "Magnetic effects of direct current in coils. Earth magnetic field determination".

4. Didactic field

The equipment can be used from secondary to the University.