(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
(i) See picture i have uploaded.
Step down transformer works on the principle of "Faraday’s law of electromagnetic induction”. Faraday’s law states that “when the magnetic flux linking a circuit changes, an electromotive force is induced in the circuit proportional to the rate of change of the flux linkage”.
(ii) The emf (Electro Motive Force) induced between the two windings is determined by the number of turns in primary and secondary winding respectively. This ratio is called as Turns Ratio.
The formula used to design a Step Down Transformer is:
Ns/Np=Vs/Vp ,
where Ns- no. of turns in secondary coil. Np- no. of turns in primary coil. Vs- Voltage in secondary coil. Vp- Voltage in primary coil.
(iii) In ideal transformer, there will be no flux losses and the Voltage appearing at secondary must equal to Voltage appearing at primary coil. So Vs=Vp
Therefore, Ns/Np=1:1
(iv) Since Power=V*I
So, we have given that Power= 550W
Voltage V= 110V
So, Current I=P/V
I=550/110
I=5 Amps