Clill activity

1. Clill activity: report of Faraday’s experiments
By Federico Bianco
Purpose:
Understanding the phenomenonof “Electromagnetic induction”
(which demonstrates how a variablemagnetic field or other
features can generate an inducedcurrent) through Faraday’s
experiments
Materials:
The two experiments provide:
 Ammeter
 Solenoid
 Magnetic bar
 Rectangularcircuit with two fixed sides
 Conductivebar
 Ferromagnetic bar in shape of horshoe
 Lamp
Procedures:
1’ Experiment:
As well as Faraday,we connected the
solenoid,with N windings, to an
ammeter, which initiallyreported that
there was no current. Then we started to
move the magnetic bar around and
For the firstone
For the second one

2. inside the solenoid,seeing how the ammeter marked the
presence of current.
2’ Experiment:
It consists of a rectangular circuit,
where the barcan moves on the two
fixed guides, connected with the lamp
and placed between the polarpieces
of a ferromagnetic bar in shape of
horseshoe (Because of this the circuit
is immersed into a uniform magnetic
field). Despite there isn’t any voltage
generator, the movement of the
conductive bar causes the lighting of
the bulb.
Observations:
The experiments show that both the movement of the magnetic
bar and both the translation of the conductive bar produce an
induced current, confirmed by the ammeter and by the lamp,
which depends by the variationsof the magnetic field and of the
covered surface. (Superficie percorsa)
Conclusion:
Despite the lack of a voltage generator, the electromagnetic
inductionallowsthe productionof corrent, due to:

3.  In the first case, the inductioncomes from the mobility of
the magnet, which produces a variablemagnetic field that
induces an inducedEMF. This one generates an induced
current in the solenoid.
 In the second case, the inductioncomes from the mobility
of the conductive bar, which produces the variation, over
time, of the surface of the circuit. Just for this reason inside
the bar appearsan inducedEMF which generates an
induced current into the circuit and, therefore, the lighting
of the bulb.
-------------------------------------------------------------------------
Anyway, the common thing of the two cases is that the
variationsof the magnetic field and of the covered surface
always produce a variable magnetic flux, considered by
Faraday the reason why electromagnetic inductionoccurs.
From this knowledge, he elaboratesthe:
“Faraday-Neumann’s law”:
Which included “Lens’s law” too:
The negative sign of the formula is due to Lenz who
understood how the induced currents produced induced

4. magnetic fields that opposed the flux variation that had
generated them.