A step up transformer is used to

Explanation

No, there is no gain of energy in ideal situation. Let us assume that there is no power involed, then according to energy conservation, the energy inversted at primary coil must be same as energy output at secondary coil power is voltage multiplied with current. when voltage is changed for secondary coil, then corresponding current also changes so that product of voltage and current for the primary coil is same as that for the secondary coil for transformer we can write .
Power = `V_(p)l_(p) = V_(s) I_(s)`
`rArr " " (V_(p))/(V_(s)) = (I_(s))/(I_(p))`
Let `N_(s) and N_(p)` be the number of turns in secondary coil and primary coil, respectively. then we can write
`rArr " " (V_(p))/(V_(s)) = (N_(p))/(N_(s))`
Using equations (i) and (ii) we can write the following :
` rArr " " (I_(p))/(I_(s)) = (N_(s))/(N_(p))`
From equation (ii) and (iii) we can see that voltage across primary and secondary coil is proportional to the number of turns is them. and. current flowing n these coils is inversely proportional to the number of turns.
step-up transformer changes low voltage and high current into high voltage and low current , respectively. Step-down transformer changes high voltage and low current into low voltage and high current , respectively. hence, when voltage is increased then current is reduced and when voltage is decreased then current is increased, but the product of voltage and current hence power remains same across primary and secondary coil .