Working of a step down transformer:
A step down transformer converts a high voltage at the primary side to a low voltage at the secondary side.
Transformer work on the principle of "Faraday's law of electromagnetic induction".
The emf induced is determined by the number of turns in primary and secondary windings. This ratio is called as Turn Ratio.
The voltage reduction capability of step down transformers depends on the turn ratio of the primary and secondary coils. As the number of turns in secondary coil is kept less as compared to the number of turns in primary coil, so the amount of flux linkage to the secondary coil of the transformer is less compared to the primary coil. Accordingly, the emf induced will be less in the secondary coil.
‌

NS

Np

=‌

VS

Vp

Here,
N s‌=‌ number of turns in secondary coil ‌
Np‌=‌ number of turns in primary coil ‌
‌Vs=‌ Voltage in secondary coil ‌
‌Vp=‌ Voltage in primary coil ‌
The number of turns in secondary winding is always less than the number of turns in the primary winding of the transformer, i.e. Np>N s.
As the number of turns is less in secondary coil, so the induced emf (output voltage) in the secondary coil will be less than the primary input voltage.
Laminated iron core is used in transformers to reduce the Eddy current which prevents the efficient transfer of energy from the primary coil to the secondary coil and causes energy loss in form of heat generation in the core.