what is a transformer? what is its principle of working? why efficiency of a transformer is less than 100%? whya transformer cannot be used to step up or step down dc voltage?
Transformer is a device that can be used to convert high voltage AC to low voltage AC (step down) or low voltage AC to high voltage AC (step up). It contains two coils: primary coil and secondary coil. Input AC is given to the primary coil and output AC is obtained in the secondary coil.
Transformer works on the principle of mutual induction. Here a changing AC in the primary coil produces a changing magnetic field which in turn induces a changing AC in the secondary coil.
In step up the output voltage of the transformer is larger than the input voltage and output current is lesser than the input current. A step up transformer has number of turns in secondary (Ns) greater than the number of turns in the primary (Np). If Ep = input voltage, Es = output voltage then,
In step down the output voltage of the transformer is smaller than the input voltage and output current is more than the input current. In step down transformer the number of turns in primary (Np) is more than number of turns in secondary (Ns). So, following the above steps we finally find Ep > Es and Ip < Is.
Efficiency of a transformer is = Output power/Input Power
The efficiency of a transformer is less than 100% because there is always some power loss due to eddy current, hysteresis, flux leak etc.
Since, a transformer works on the principle of mutual induction it will not work for DC voltage.