A group of students while coming from the school noticed a box marked “Danger H.T. 2200 V” at a substation in the main street. They did not understand the utility of such a high voltage, while they argued; the supply was only 220 V. They asked their teacher this question the next day. The teacher thought it to be an important question and therefore explained to the whole class.

Answer the following questions:

(i) What device is used to bring the high voltage down to low voltage of a.c. current and what is the principle of its working?

(ii) Is it possible to use this device for bringing down the high dc voltage to the low voltage? Explain.

iii) Write the values displayed by the students and the teacher. 

i) The device which is used to bring the high voltage down to low voltage is step down transformer. The working principle of step down transformer is mutual induction. Whenever there is change in current in one circuit, emf is induced in the neighboring circuit.

ii) Transformer cannot be used to bring down the high d.c voltage to low voltage because its working is based on electromagnetic induction, which is associated with varying magnetic flux. But, current is constant for a d.c source. So, magnetic flux will not vary. Hence, output cannot be obtained from the transformer.

iii) There is a curiosity among the students to gain knowledge. And the teachers are able to make use of their knowledge and impart it to students to explain the practical application.