SOLUTION

From emf equation of transformer

$E = 4.44fNAB$

Where
E= Voltage
f= frequency
A= Area of the core
N= number of turns
B =magnetic flux density

In general, we can say

A = E/(4.44fNB)

• For the constant value of E, N, B if we increase F, then the Area of the core will decrease means the size of the transformer will reduce.
• The Frequency is inversely proportional to the A-area of the Transformer. As the Frequency is High, the Size and Weight of the Transformer of the same power Rating can be reduced.
• Higher frequency implies faster MMF variations with time hence higher emf is inducted on coils, then for same voltage lower core area is needed or lower number of turns, in any case, lower volume.

The size of the transformer core depends on both the frequency and area of the core.

The flux is proportional to the ratio of voltage/frequency. The higher the frequency lower is the flux in the transformer and vice versa. So, at higher frequencies the operating flux in the transformer core is low. That means there is no point in using a lot of magnetic material in the core to handle that flux which reduces the size of a transformer.

But if we operate a transformer at low frequencies the build has to be a big one. Large flux would need a larger core thus increasing the size of a transformer.