Question

A transformer is an electrial device which is used for changing the a.c. voltages. It is based on the principle of mutual induction, i.e., whenever the amount of magnetic flux linked with a coil changes, an e.m.f. is induced in the neighbouring coil. For an ideal transformer, `(E_(s))/(E_(P)) = (I_(P))/(I_(s)) = (n_(s))/(n_(P))` where the symbols have their usual meaning
Read the above passage adn answer the following question :
(i) A transformer has 20 turns in primary and 200 turns in seconday. If the primary is connected to 220 V d.c. supply, what will be the voltage across secondary ?
(ii) The output voltage of an ideal tansformer connected to 240 V a.c. mains is 24 V. When this transformer is used to light a bulb with rating 24 V, 24 W, what is thr primary current ?
(iii) What values of life do you learn from the theory of transformer ?

Answer 1

(I) Here, `n_(p) = 20, n_(s) = 200, E_(p) = 220 V d.c., E_(s) = ?` Voltage acorss seconday will be zero, as transformer does not work on d.c. It is based on mutual induction.
(ii) Here, `E_(p) = 240 V, E_(s) = 24 v, I_(s) = (P_(0))/(E_(s)) = (24)/(24) = 1 A, I_(p) = ?`
From `(E_(s))/(E_(P)) = (I_(P))/(I_(s)) , I_(P) = (E_(s) xx I_(s))/(E_(P)) = (24 xx 1)/(240) = 0.1 A`
(iii) The relation `(E_(s))/(E_(P)) = (I_(P))/(I_(s))` show that for a step up transformer , `E_(s) gt E_(P) :. I_(P) gt I_(s)` or `I_(s) lt I_(P)`
i.e., when a transformer raises the a.c. voltage, alternating current reduces in the same ratio. For example,
if a.c. voltage becomes 100 times, output alternating current becomes `(1)/(100)` time.
In day to day life, we find that you cannot gain on all fronts, neither you will lose on all fronts. The gains and losses go together. Gain of one is loss of the other. In life, you have to weigh your priorities and act to meet them keeping in ming the above principle.