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 = `"N"_"s"/"N"_"p" = "E"_"s"/"E"_"p"`

`"N"_"s"/"N"_"P" = 50/250 = 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 = `"I"_"p"/"I"_"s" = "E"_"s"/"E"_"s" = 1/5`

I_p = `1/5 xx 2 = 0.4 "A"`