A 60 W load is connected to the secondary of a transformer whose primary draws line voltage. If a current of 0.54 A flows in the load, what is the current in the primary coil ? Comment on the type of transformer being used.

Explanation

`P_S`=60 W, `I_S`=0.54 A
`I_P`= ? , Line voltage `V_P`= 220 V
`P_S=V_S I_S`
`therefore V_S=P_S/I_S=60/0.54` =111.1 V
`therefore V_S approx` 110 V
`therefore V_S lt V_P` hence , step-down transformer is used.
The transformation ratio,
`r=V_S/V_P=I_P/I_S`
`therefore I_P=I_S xx V_S/V_P`
`=0.54xx110/220`
`therefore I_P`=0.27 A