The Foucault current
Coils, solenoids and other things
Measurement of a magnetic field
Magnetic properties of materials
And if there's no variation in flow?
The rotating magnetic field
High frequency fields
INTERACTIVE EXPERIMENTS AND EXHIBITS
In our daily lives we use innumerable objects that work because of phenomena determined by interactions between electric currents, between currents and magnetic fields and currents that interact with themselves. All generators and electric motors, as well as many other apparatuses and devices are based on these phenomena.
This is the "dynamo" created by Antonio Pacinotti (1841-1912) some time around 1859-60, one of the inventions that have transformed our world, making available unlimited amounts of electricity and determining what has been called the “second industrial revolution".
Below is a portrait of Pacinotti with his first "Macchinetta" (little machine)...
and the diagram of its “ring” inductor with the commutation brushes to obtain unidirectional current, the fundamental idea behind the invention.
Among today’s applications, here is the appearance and size that machines for the generation of electricity have assumed since the first one made by Pacinotti
This is a normal loudspeaker (all reproduced sounds reach our ears from speakers like these) from which the magnet has been removed. The mobile bobbin with a thin red enamelled wire moves in the air gap of the ring magnetic field generated by a permanent magnet and transmits its movement to the cone.
This is the earphone of a headphone. On the left is the thin membrane with its mobile bobbin; on the right the magnet with the ring air gap.
The complete earphone, identical to the capsule of a dynamic microphone, is shown below:
Another widespread device of the greatest importance
An ignition coil for automobile internal combustion engines, a small Ruhmkorff coil immersed in oil which, starting from the 12 V alternating current of the battery, generates impulses of 15 kV for the sparking plugs, here used as a small spark radio transmitter:
and a 200 W electric motor with brushes made from a household beater: it runs on both alternating and direct current...
All radios, television sets, cell phones and satellite communications devices are concentrates of applications in the field of electromagnetics...
this is a domestic radio receiver with valves from the 1930s
...up to extremely delicate and highly sophisticated devices, such as the hard disks in our computers, in which there is a complex of technological applications of electromagnetic phenomena. Observe for example the working of the microscopic magnetic heads for reading and writing:
and how the synchronous motor maintains the rotation of the stack of magnetic disks at a perfectly constant speed:
Later we’ll see some experiments on the fundamental principles of electromagnetism accompanied by brief explanations. Note that they are all performed with apparatuses built in our laboratory with the specific intention of making them as simple as possible so that anyone can duplicate them with the use of the smallest number of tools and equipment. It is for this reason that we have avoided using apparatuses and accessories that are normally found in laboratories such as rods, supports, power supplies, wires with banana clips and so on.