Answer :
Final answer:
A transformer cannot step-up DC voltage because it requires a changing magnetic field, according to Faraday's law of induction, to induce voltage on the secondary coil. DC provides a constant voltage with no changing magnetic field, hence no induction and no motor movement.
Explanation:
A small electric motor will not spin when connected to the secondary coil of a step-up transformer if the primary coil is connected to a DC battery because transformers are designed to work with alternating current (AC), not direct current (DC). This is due to Faraday's law of induction, which states that a changing magnetic field is required to induce voltage in the secondary coil.
Since DC provides a constant voltage, there is no variation in the magnetic field, and thus no induction takes place. Should DC be switched on and off rapidly, a type of pulsating DC, it could create a changing magnetic field, but this is not efficient for practical purposes. Therefore, AC is commonly used where changes in voltage are necessary because it inherently provides the changing magnetic field needed for transformer operation.
