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  • (i) Draw a labelled diagram of a step-down transformer. state the principle of its working. (ii) Express the turn ratio in terms of voltages. (iii) Find the ratio of primary and secondary currents in terms of turn ratio in an ideal transf

(i) Draw a labelled diagram of a step-down transformer. state the principle of its working.
(ii) Express the turn ratio in terms of voltages.
(iii) Find the ratio of primary and secondary currents in terms of turn ratio in an ideal transformer.
(iv)How much current is drawn by the primary of a transformer connected to 220 V supply when it delivers power to a 110 V -550 W refrigerator?

 

 

 

 
 
 
 
 

Answers (1)

(i)
 
Transformer work on the principle of mutual induction when an alternating input is applied in the primary, the resulting current produces a magnetic flux in the secondary coil and an emf is induced in the secondary coil.
(ii) If the number of turns in the primary coil and secondary coil are N1 and N2 respectively and Vp is primary voltage and the voltage across secondary is Vs, then
 \frac{V_{s}}{V_{p}}= \frac{N_{s}}{N_{p}}
(iii) In an ideal transformer, that is if the transformer is considered to be 100 % efficient
then input power = output power
i_{p}V_{p}= i_{s}V_{s}
\frac{i_{p}}{i_{s}}= \frac{V_{s}}{V_{p}}= \frac{N_{s}}{N_{p}}
(iv) Current in the secondary
  = \frac{550}{110}= 5\cdot 5A
\frac{N_{s}}{N_{p}}= \frac{V_{s}}{V_{p}}= \frac{220}{110}= 2
\frac{I_{p}}{I_{s}}= \frac{N_{s}}{N_{p}}= 2
I_{p}= 2\times I_{s}
     I_{p}= 2\times I_{s}
          = 2\times 5\cdot 5
         = 11 A
 

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Safeer PP

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