How does a transformer work?

Transformer - Function

Viewing (ideal) unloaded transformer

By neglecting the losses, the following formulas can be derived:

For the unloaded transformer, i.e. no load connected:

N₁  =   N₂            (1)
V₁       V₂

We verify our assertion with the values from the video:

V₂ =   N₂  *  V₁  =  300  *  100 V  =  25 V
.          N₁                 1200

Loaded ideal transformer:

When a load is connected, the output voltage V₂ can and will drop. How much it drops depends on the load (output current I₂) and how the transformer is designed.

If losses are neglected, however, the output power is equal to the input power:

.           P₁              =    P₂

=>       V₁  *  I₁   =   V₂  *  I₂       (2)

Eq. (1) in eq. (2) shows the relationship between current and number of windings:

I₂ =   N₁   * I₁
.         N₂