PERCORSI DIDATTICI IL PROCESSO DI TRASFORMAZIONE STORIA-SISTEMI-INGLESE

1. ROVOLUZIONE RUSSA

2. ITALIA DALLA MONARCHIA ALLA REPUBBLICA

3. LA TRASFORMATA DI LA PLACE

3.1. associa ad una funzione di variabile reale una funzione di variabile complessa.

3.2. da f(t) a f(s)

4. secolo breve

4.1. conflitti bellici e scontri ideologici

4.2. cambiamenti sociali e culturali

4.3. Eric Hobsbawm,

5. trasformatore inglese

5.1. Transformer is an electric, static machine. It consists of two coils wound upoun a single core. Transformer is able to transform alternative voltage and current from high to low values and viceversa; current is the same in all parts of a series circuit, so the current induced in one turn will flow through the other coil. We can say that the power consumed by the secondary is the same as the power consumed by the primary ( when the voltage steps up the current steps down ). Transformer follows the law of the conservation of energy that say that the output power can’t be graeter than the input power, the input power is equal to the output power. There are two type of transformers: Step-up transformer and Step-down transformer. In the step-up transformer the voltage of the secondary is more than the voltage of the primary, on the contrari the current in the secondary is less than the current in the primary; in a step – up transformer the ratio between the number of turns of the secondary and the number of turns in the primary is more than one. In the step-down transformer, is the contrary of the step – up transformer. To encrase the electromotivforce we have to encrease the number of turns; so, for example, in a Step – up transformer the number of the turns of second coil is more than the number of turns of the first coil. Coefficient of coupling is the strength of mutual indactance* between two coils. ( * Mutual indactance: is the propriety that links the two coils; it dipends on the distance of the two coils, if two coils are very near mutual indactance is high, on the contrary if the two coils are far mutual indactance is low). The coils can be loosely coupled or closely coupled; in the first conditon two coils are placed so that, only a few of their magnetic lines of force interact; in the second case the two coils are placed very close to each other so most of the lines of force, from each coil cut across the other. In theory ( caso ideale ) maximum quantity of cupling between two coils is 100%; this phenomenon occurs when all of the magnetic lines of one coil cut across all of the turn of the other, and viceversa. In pratice ( caso reale ) 100% coupling can never be totally achieved, but you can encrease coupling if both coils are wound upon a single core. The transformer losses: A source of energy loss in a transformer is the resistance. Resistance usually has a small value, in a transformer, so it produces only a small voltage loss. Another important type of energy loss in a transformer is iron loss; there are two important kind of iron losses type: hysteresis loss and eddy current ( corrente parassita ). Hysteresis loss is the loss caused by the change of the positon of atoms caused by the ch’ange of direction of the current and the magnetic field; it can be reduced constructing the core of some material that is very easy to magnetize and demagnetize ( for example, slicon steel). Eddy current is the current that is induced in the conductive core by the fluctuating magnetic field of the coils; to reduced eddy current, transformer cores are often made of a pile of very thin metallic sheets called laminations; laminations are insulated from each other, by a layer (strato) of varnish of oxide.