A DC machine is an electromechanical energy alteration device. The working principle of a DC machine is when electric current flows through a coil within a magnetic field, and then the magnetic force generates a torque which rotates the dc motor whereas a transformer is an electrical equipment used to transfer electrical energy from one electrical circuit to another, or multiple circuits without changing the frequency. Transformers can also be used for isolation, where the voltage in equals the voltage out, with separate coils not electrically bonded to one another.