A step down transformer is used at 220 V to provide a current of 0.5 A to a 15 W bulb. If the secondary has 20 turns, find the number of turns in primary coil has current that flows in primary coil.

Explanation

Here, `E_(P) = 220 V, I_(s) = 0.5 A, P_(s) = 15 W`,
`n_(s) = 20, n_(P) = ? I_(P) = ?`
`E_(s) = (P_(s))/(I_(s)) = (15)/(0.5) = 30 V`
As `(E_(P))/(E_(s)) = (n_(P))/(n_(s)) :.n_(P) = (E_(P))/(E_(s)) xx n_(s) = (220)/(30) xx 20`
= 147
Also, from `E_(P) I_(P) = E_(s) I_(s)`
`I_(P) = (E_(s) I_(s))/(E_(P)) = (P_(s))/(E_(P)) = (15)/(220) = 0.068 A`