Question

Fig . shows the core of a transformer and i ts input and output connections 

State the material used for the core and describe th e structure of the core.
(a) Use the values given in the diagram to calculate the turns ratio for the transformer and connections, labeling all parts of the diagram .
(b) If a current of 2 A is taken from th e output, calculate th e current in the input circuit (Assume the transformer to be ideal ).

Answer 1

(a) Soft iron is used as the material for the core of transformer.
Structure of core: The core is made by taking thin rectangular sheets or laminas of soft iron (or silicon -steel) and dipping them in an insulating paint or varnish . These insulated sheets are stacked together to form a solid looking rectangular frame. This is called the laminated core of the transformer.

(b) Given, E_p = 250 V, E. =50 V

We know that for transformer turn ratio = ${\displaystyle \frac{{\text{N}}_{\text{s}}}{{\text{N}}_{\text{p}}}=\frac{{\text{E}}_{\text{s}}}{{\text{E}}_{\text{p}}}}$

${\displaystyle \frac{{\text{N}}_{\text{s}}}{{\text{N}}_{\text{P}}}=\frac{50}{250}=\frac{1}{5}}$

Thus, it is a step-down transformer. 

Given, I_s =2A

Let I_p be the current though primary.

We know that for transformer turn ratio = ${\displaystyle \frac{{\text{I}}_{\text{p}}}{{\text{I}}_{\text{s}}}=\frac{{\text{E}}_{\text{s}}}{{\text{E}}_{\text{s}}}=\frac{1}{5}}$

I_p = ${\displaystyle \frac{1}{5}\times 2=0.4\text{A}}$