At a substation a box is marked "Danger — H.T. 2200 V".
(i) Which device is used to bring a high AC voltage down to a low AC voltage, and what is the principle of its working?
(ii) Is it possible to use this device to bring a high DC voltage down to a low voltage? Explain.
(i) Which device is used to bring a high AC voltage down to a low AC voltage, and what is the principle of its working?
(ii) Is it possible to use this device to bring a high DC voltage down to a low voltage? Explain.
Answer: (i) A (step-down) transformer, working on mutual induction.
(ii) No — a transformer cannot work on steady DC.
Solution
(i) The device is a step-down transformer. It works on the principle of mutual induction: an alternating current in the primary produces a changing flux in the core, which links the secondary and induces an emf there. With fewer turns on the secondary than the primary, the output voltage is reduced.
(ii) No. A steady DC in the primary gives a constant flux, so and no emf is induced in the secondary. A transformer therefore cannot step a steady DC voltage up or down.
(ii) No. A steady DC in the primary gives a constant flux, so and no emf is induced in the secondary. A transformer therefore cannot step a steady DC voltage up or down.
CBSE Class 12 Board · 2015 · Delhi · Subjective